文章
Dummer. ゛☀
2017年09月19日
Oak wilt is a systematic disease caused by a fungus, Ceratocystis fagacearum. The fungus invades the water-conducting tissues of oak trees. The black oak group (red, black, scarlet, and pin oaks) is more susceptible than the white oak group (white, bur, chinkapin, and swamp oaks). Oak wilt ranges from Minnesota east to Pennsylvania, south to South Carolina and Tennessee, west to central Texas, and north through Kansas and Nebraska. Infection through wounds is especially critical between April 1 and July 1 and during later periods of summer rains. There is no cure for oak wilt, so control consists of measures to prevent the disease from spreading.
Symptoms and Diagnosis
The first symptoms include a dull-green appearance of wilted leaves. Later, wilted leaves curl and turn tan or bronze, beginning at the outer portions of the leaves. The base of the leaf and the main vein will remain green for some time. Defoliation may be delayed for weeks. Peeled bark or a cut branch from an infected tree may show a brown or black discoloration in the outer annual sapwood ring. Positive diagnosis of oak wilt requires laboratory culturing and identification.
Life Cycle
The fungus spreads through the water-conducting vessels of the sapwood. The tree’s response to the presence of the fungus results in the disruption of sap flow, and the affected areas wilt. Oak wilt can spread to healthy trees through natural grafts with roots of adjacent oaks of the same species up to 50 feet apart. Root grafts join together the vascular systems of the trees, forming a network through which the disease can spread. The disease can also spread by sap-feeding beetles that transmit spores of the oak wilt fungus from infected trees to healthy ones.
Integrated Pest Management Strategies
1. There is no cure for the disease. If oak wilt is suspected, a laboratory test is needed to make a positive diagnosis. Contact an arborist or an extension office on sampling procedures and fees associated with the laboratory testing. Samples of freshly wilted stems (not dead) about 1/2 to 1 inch in diameter and 6–10 inches in length are needed for the laboratory test.
2. Sever root grafts. Destroying root grafts with chemicals or by mechanical means can slow the spread of the disease from diseased to healthy oak trees. Since there is a delay between infection and the appearance of symptoms, destroying root grafts is a gamble. Root grafts do not occur between the black oak and white oak groups.
3. Improve plant vigor. Your best guard against getting oak wilt is to keep your oak trees, especially oaks in the black oak group, healthy. If your oak trees do not appear in the best of health, have an experienced arborist evaluate their health and recommend a course of action. Mild cases in white oaks may respond to pruning of diseased wood plus fertilizing and watering to increase plant vigor.
4. Avoid pruning or wounding the tree between mid-March and late June. During this time of year, insects carrying the disease are attracted by the sap which flows freely from wounds. The safest time to prune oaks is during winter before mid-March.
5. Plant white oaks rather than the more susceptible black oaks. If you do plant black oaks, be certain they are more than 50 feet apart to eliminate future disease spread via root grafts. Limit black oak use where oak wilt is prevalent.
Symptoms and Diagnosis
The first symptoms include a dull-green appearance of wilted leaves. Later, wilted leaves curl and turn tan or bronze, beginning at the outer portions of the leaves. The base of the leaf and the main vein will remain green for some time. Defoliation may be delayed for weeks. Peeled bark or a cut branch from an infected tree may show a brown or black discoloration in the outer annual sapwood ring. Positive diagnosis of oak wilt requires laboratory culturing and identification.
Life Cycle
The fungus spreads through the water-conducting vessels of the sapwood. The tree’s response to the presence of the fungus results in the disruption of sap flow, and the affected areas wilt. Oak wilt can spread to healthy trees through natural grafts with roots of adjacent oaks of the same species up to 50 feet apart. Root grafts join together the vascular systems of the trees, forming a network through which the disease can spread. The disease can also spread by sap-feeding beetles that transmit spores of the oak wilt fungus from infected trees to healthy ones.
Integrated Pest Management Strategies
1. There is no cure for the disease. If oak wilt is suspected, a laboratory test is needed to make a positive diagnosis. Contact an arborist or an extension office on sampling procedures and fees associated with the laboratory testing. Samples of freshly wilted stems (not dead) about 1/2 to 1 inch in diameter and 6–10 inches in length are needed for the laboratory test.
2. Sever root grafts. Destroying root grafts with chemicals or by mechanical means can slow the spread of the disease from diseased to healthy oak trees. Since there is a delay between infection and the appearance of symptoms, destroying root grafts is a gamble. Root grafts do not occur between the black oak and white oak groups.
3. Improve plant vigor. Your best guard against getting oak wilt is to keep your oak trees, especially oaks in the black oak group, healthy. If your oak trees do not appear in the best of health, have an experienced arborist evaluate their health and recommend a course of action. Mild cases in white oaks may respond to pruning of diseased wood plus fertilizing and watering to increase plant vigor.
4. Avoid pruning or wounding the tree between mid-March and late June. During this time of year, insects carrying the disease are attracted by the sap which flows freely from wounds. The safest time to prune oaks is during winter before mid-March.
5. Plant white oaks rather than the more susceptible black oaks. If you do plant black oaks, be certain they are more than 50 feet apart to eliminate future disease spread via root grafts. Limit black oak use where oak wilt is prevalent.
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文章
Dummer. ゛☀
2017年09月19日
Most plants growing in average garden soil in the St. Louis area receive sufficient nutrients from the soil that deficiencies are not a problem. The most notable exception is iron chlorosis of trees and shrubs, which is more likely to result from a high soil pH than a lack of iron in the soil. See below for more information on this deficiency. Also, because of the higher nitrogen requirement of turf grasses and leafy vegetables in the vegetable garden they may benefit from some additional nitrogen fertilizer. Also, nutrient deficiencies are likely to occur in plants growing in containers that are not fertilized regularly because of the reduced soil volume and the lower nutrient holding capacity of soil-less mixes used for container plants.
Following is some brief information on the symptoms of common nutrient deficiencies:
Macronutrients
Nitrogen
Lack of nitrogen shows up as overall yellow-green leaves instead of a dark green, yellowing and dropping of lower leaves (can be caused by many factors), and overall reduced plant size and slow growth. Although most garden plants receive adequate nitrogen from the soil and dissolved in rainwater, applying nitrogen in a complete, balanced fertilizer such as 20-20-20 once a year around perennials and shrubs is usually sufficient to provide adequate growth. Leafy vegetables can benefit from additional nitrogen. Most trees do not suffer from lack of sufficient nitrogen. Although lawns respond quickly and dramatically to the application of nitrogen, becoming green and lush, its use should be tempered, as this lush growth is also more susceptible to attack by insects and disease. Nitrogen in best applied to cool-season grasses in fall and on warm season grasses as they begin to grow in early summer. Nitrogen should be applied to container plants in a complete fertilizer, such as 20-20-20.
Phosphorus
Lack of phosphorus typically results in reduced growth and in some plants purplish foliage, especially older leaves. Although it may be observed on container grown plants most soils in Missouri contain ample phosphorus so more rarely would deficiencies be noticed in a garden situation. If you suspect your plants are showing symptoms of lack of phosphorus, have your soil tested. Then add phosphorus as required by the test results. Container grown plants require regular fertilizing with a complete fertilizer such as 20-20-20.
Potash
Again, lack of potash is rare in Missouri soils but deficiency symptoms typically result in stunted growth. Older leaves may yellow and leaf edges may roll up. If a deficiency is suspected have your soil tested and follow the recommendations provided with your soil test results. Container grown plants require regular fertilizing with a complete fertilizer such as 20-20-20.
Calcium, Magnesium and Sulfur
These three elements complete the macronutrients. They are frequently available in adequate amounts in St. Louis soils.
Micronutrients
Several micronutrients are required for good plant growth. These include: iron, manganese, copper, zinc, boron, chlorine, molybdenum, and nickel. Symptoms are almost entirely crop specific, hence, listing general symptoms of little use. Also, their identification can be difficult from symptoms alone. Some are well known and a plant disease reference of well-studied crops may show pictures of the classic symptoms of a particular nutrient deficiency on a crop. Frequently, however, short of sending leaf tissue off to a lab for analysis the gardener is left questioning whether the symptoms they are seeing are caused by a nutrient deficiency or not. If in doubt, treat the plant with a micronutrient fertilizer or a complete fertilizer containing micronutrients. Since most micronutrients are used in very small amounts the fertilizer will provide the plant what it needs if the soil is indeed lacking in a micronutrient. Follow the product’s label directions. In the St. Louis area the most commonly encountered micronutrient problem is with iron.
Iron
Lack of iron most notably causes what is referred to as iron chlorosis or yellowing leaves where the veins remain green. New growth is most affected. Lack of iron in the soil, a high soil pH (over 7) that restricts availability of iron in the soil, and environmental conditions can all result in iron chlorosis. For detailed information on iron chlorosis see the IPM page “Iron Chlorosis of Trees and Shrubs” herein. Potted plants showing iron chlorosis can be watered with a fertilizer containing iron or a specific iron fertilizer such as chelated iron.
Following is some brief information on the symptoms of common nutrient deficiencies:
Macronutrients
Nitrogen
Lack of nitrogen shows up as overall yellow-green leaves instead of a dark green, yellowing and dropping of lower leaves (can be caused by many factors), and overall reduced plant size and slow growth. Although most garden plants receive adequate nitrogen from the soil and dissolved in rainwater, applying nitrogen in a complete, balanced fertilizer such as 20-20-20 once a year around perennials and shrubs is usually sufficient to provide adequate growth. Leafy vegetables can benefit from additional nitrogen. Most trees do not suffer from lack of sufficient nitrogen. Although lawns respond quickly and dramatically to the application of nitrogen, becoming green and lush, its use should be tempered, as this lush growth is also more susceptible to attack by insects and disease. Nitrogen in best applied to cool-season grasses in fall and on warm season grasses as they begin to grow in early summer. Nitrogen should be applied to container plants in a complete fertilizer, such as 20-20-20.
Phosphorus
Lack of phosphorus typically results in reduced growth and in some plants purplish foliage, especially older leaves. Although it may be observed on container grown plants most soils in Missouri contain ample phosphorus so more rarely would deficiencies be noticed in a garden situation. If you suspect your plants are showing symptoms of lack of phosphorus, have your soil tested. Then add phosphorus as required by the test results. Container grown plants require regular fertilizing with a complete fertilizer such as 20-20-20.
Potash
Again, lack of potash is rare in Missouri soils but deficiency symptoms typically result in stunted growth. Older leaves may yellow and leaf edges may roll up. If a deficiency is suspected have your soil tested and follow the recommendations provided with your soil test results. Container grown plants require regular fertilizing with a complete fertilizer such as 20-20-20.
Calcium, Magnesium and Sulfur
These three elements complete the macronutrients. They are frequently available in adequate amounts in St. Louis soils.
Micronutrients
Several micronutrients are required for good plant growth. These include: iron, manganese, copper, zinc, boron, chlorine, molybdenum, and nickel. Symptoms are almost entirely crop specific, hence, listing general symptoms of little use. Also, their identification can be difficult from symptoms alone. Some are well known and a plant disease reference of well-studied crops may show pictures of the classic symptoms of a particular nutrient deficiency on a crop. Frequently, however, short of sending leaf tissue off to a lab for analysis the gardener is left questioning whether the symptoms they are seeing are caused by a nutrient deficiency or not. If in doubt, treat the plant with a micronutrient fertilizer or a complete fertilizer containing micronutrients. Since most micronutrients are used in very small amounts the fertilizer will provide the plant what it needs if the soil is indeed lacking in a micronutrient. Follow the product’s label directions. In the St. Louis area the most commonly encountered micronutrient problem is with iron.
Iron
Lack of iron most notably causes what is referred to as iron chlorosis or yellowing leaves where the veins remain green. New growth is most affected. Lack of iron in the soil, a high soil pH (over 7) that restricts availability of iron in the soil, and environmental conditions can all result in iron chlorosis. For detailed information on iron chlorosis see the IPM page “Iron Chlorosis of Trees and Shrubs” herein. Potted plants showing iron chlorosis can be watered with a fertilizer containing iron or a specific iron fertilizer such as chelated iron.
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文章
Dummer. ゛☀
2017年09月19日
Worldwide, Nectria fungi cause several common canker and dieback diseases, especially in hardwood trees. Nectria canker, which is caused by the fungus, Nectria galligena, may occur on over 60 species of trees and shrubs including apple, ash, birch, dogwood, elm, sweet gum, holly, maple, pear and walnut. A similar disease infects members of the magnolia family. Nectria canker is usually not a fatal disease, but it can cause considerable damage as the cankered area is weakened and susceptible to breakage. It may also adversely affect the appearance of the affected plant. This disease is important commercially as it reduces the quality and quantity of forest products.
Another member of the Nectria genus, Nectria cinnabarina, causes the disease Nectria dieback. Also known as coral spot Nectria canker or Nectria canker, this disease occurs on many plant species, including apple, ash, barberry, birch, boxwood, crabapple, elm, hickory, honey locust, linden, maple, pear, rose and Japanese zelkova. Nectria cinnabarina usually grows as a saprophyte on dead wood, but if a plant is wounded or otherwise stressed, the fungus becomes an opportunistic weak parasite, producing cankers and causing dieback of twigs and branches. Maples are especially affected by this disease as are recently wounded or severely pruned trees and shrubs, urban ornamentals and new transplants of other species.
Symptoms and Diagnosis
Although it is most common in spring and fall, the Nectria fungus can infect plants throughout the year as long as there is sufficient moisture and the temperature is above freezing. Plants that are stressed by cold, drought, mechanical injuries or other disease are especially susceptible. Infections may be worse in autumn and winter when the host plant is dormant and wound recovery is weaker than in the growing season.
The first symptom of a Nectria infection is a depressed discolored area of bark near wounds or at the base of dead twigs or branches. These cankers are usually not noticed until other symptoms appear.
The first easily visible signs of Nectria canker are small creamy white or red to reddish orange fruiting structures and the development of callus tissue. This callus tissue is produced as the host plant attempts to isolate the fungus. If the callus does not isolate the infection, the fungus will continue to grow into healthy wood and the plant will respond by growing another ridge of callus tissue. This alternation of fungal growth and callus ridge, which may occur for many years, results in a rounded or elongated target-like shape. The bark of older ridges may decay and weather away exposing the ridges of wood underneath. This disease grows slowly and larger stems are rarely girdled, although multiple lesions may grow together and kill a branch or the entire plant. Plants that are stressed are most severely affected by the disease. This fungus may also affect apple fruit causing it to rot during storage.
The first obvious sign of Nectria dieback may not occur until spring when the plant begins to grow. Affected twigs, branches, or even entire plants will not produce leaves or may wilt suddenly. Larger branches or small trees may be girdled and killed. The fungus produces reproductive structures that vary in color from creamy, coral pink, pink-orange, light purplish red or orange-red and that darken as they mature.
Life Cycle
Nectria galligena overwinters in the callus tissue growing slowly while its host is dormant. During moist periods, creamy white cushion-like fruiting structures will develop. These are followed by a second type of reproductive structure, which is red to reddish orange, pin-head sized and lemon-shaped, in autumn through spring. During rain or other moist weather, spores are released and dispersed by wind or water infecting susceptible plants through natural openings such as leaf scars or through wounds from improper pruning, sunscald, storm damage, frost cracks or other mechanical damage. As the fungus grows, it kills bark, cambium, and the outermost sapwood.
The life cycle of the Nectria dieback fungus is similar to that of Nectria canker. Creamy to coral pink to pink-orange or light purplish red spore-producing structures develop in spring or early summer. These will age to tan, brown, or nearly black. Orange-red fruiting structures, which mature to dark reddish brown and may persist through winter, are produced in summer and autumn. Both structures release spores that are dispersed by water and can invade susceptible tissue producing cankers and dieback.
Integrated Pest Management Strategies
1. Proper selection. Choose trees and shrubs that are well adapted to the climate of the area to minimize infection due to freeze damage and other environmental stresses.
2. Maintain plant vigor. Keep plants healthy and growing vigorously by using good cultural techniques. These include choosing the appropriate planting site, watering during dry periods, using mulch around the base of the tree or shrub and fertilizing and pruning properly. Pruning is best done in late winter. Avoid pruning in spring when higher moisture can increase risk of infection or in late summer and autumn, which can delay the plant’s natural cold hardiness response. Minimize any wounding due to root pruning, transplanting or lawnmowers to reduce infection sites.
3. Prune. Prune out branch cankers during dry periods when conditions are unfavorable for infection. Disinfect pruning tools in a 1-part bleach to 9-parts water solution between each cut.
Another member of the Nectria genus, Nectria cinnabarina, causes the disease Nectria dieback. Also known as coral spot Nectria canker or Nectria canker, this disease occurs on many plant species, including apple, ash, barberry, birch, boxwood, crabapple, elm, hickory, honey locust, linden, maple, pear, rose and Japanese zelkova. Nectria cinnabarina usually grows as a saprophyte on dead wood, but if a plant is wounded or otherwise stressed, the fungus becomes an opportunistic weak parasite, producing cankers and causing dieback of twigs and branches. Maples are especially affected by this disease as are recently wounded or severely pruned trees and shrubs, urban ornamentals and new transplants of other species.
Symptoms and Diagnosis
Although it is most common in spring and fall, the Nectria fungus can infect plants throughout the year as long as there is sufficient moisture and the temperature is above freezing. Plants that are stressed by cold, drought, mechanical injuries or other disease are especially susceptible. Infections may be worse in autumn and winter when the host plant is dormant and wound recovery is weaker than in the growing season.
The first symptom of a Nectria infection is a depressed discolored area of bark near wounds or at the base of dead twigs or branches. These cankers are usually not noticed until other symptoms appear.
The first easily visible signs of Nectria canker are small creamy white or red to reddish orange fruiting structures and the development of callus tissue. This callus tissue is produced as the host plant attempts to isolate the fungus. If the callus does not isolate the infection, the fungus will continue to grow into healthy wood and the plant will respond by growing another ridge of callus tissue. This alternation of fungal growth and callus ridge, which may occur for many years, results in a rounded or elongated target-like shape. The bark of older ridges may decay and weather away exposing the ridges of wood underneath. This disease grows slowly and larger stems are rarely girdled, although multiple lesions may grow together and kill a branch or the entire plant. Plants that are stressed are most severely affected by the disease. This fungus may also affect apple fruit causing it to rot during storage.
The first obvious sign of Nectria dieback may not occur until spring when the plant begins to grow. Affected twigs, branches, or even entire plants will not produce leaves or may wilt suddenly. Larger branches or small trees may be girdled and killed. The fungus produces reproductive structures that vary in color from creamy, coral pink, pink-orange, light purplish red or orange-red and that darken as they mature.
Life Cycle
Nectria galligena overwinters in the callus tissue growing slowly while its host is dormant. During moist periods, creamy white cushion-like fruiting structures will develop. These are followed by a second type of reproductive structure, which is red to reddish orange, pin-head sized and lemon-shaped, in autumn through spring. During rain or other moist weather, spores are released and dispersed by wind or water infecting susceptible plants through natural openings such as leaf scars or through wounds from improper pruning, sunscald, storm damage, frost cracks or other mechanical damage. As the fungus grows, it kills bark, cambium, and the outermost sapwood.
The life cycle of the Nectria dieback fungus is similar to that of Nectria canker. Creamy to coral pink to pink-orange or light purplish red spore-producing structures develop in spring or early summer. These will age to tan, brown, or nearly black. Orange-red fruiting structures, which mature to dark reddish brown and may persist through winter, are produced in summer and autumn. Both structures release spores that are dispersed by water and can invade susceptible tissue producing cankers and dieback.
Integrated Pest Management Strategies
1. Proper selection. Choose trees and shrubs that are well adapted to the climate of the area to minimize infection due to freeze damage and other environmental stresses.
2. Maintain plant vigor. Keep plants healthy and growing vigorously by using good cultural techniques. These include choosing the appropriate planting site, watering during dry periods, using mulch around the base of the tree or shrub and fertilizing and pruning properly. Pruning is best done in late winter. Avoid pruning in spring when higher moisture can increase risk of infection or in late summer and autumn, which can delay the plant’s natural cold hardiness response. Minimize any wounding due to root pruning, transplanting or lawnmowers to reduce infection sites.
3. Prune. Prune out branch cankers during dry periods when conditions are unfavorable for infection. Disinfect pruning tools in a 1-part bleach to 9-parts water solution between each cut.
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文章
Dummer. ゛☀
2017年09月19日
Leaf spot is a common descriptive term applied to a number of diseases affecting the foliage of ornamentals and shade trees. The majority of leaf spots are caused by fungi, but some are caused by bacteria. Some insects also cause damage that appears like a leaf spot disease. Leaf spots on trees are very common and generally do not require spraying. Leaf spot may result in some defoliation of a plant. An established plant can tolerate almost complete defoliation if it happens late in the season or not every year. Small or newly planted trees that become defoliated are more at risk of suffering damage until they become established.
Symptoms and Diagnosis
The chief symptom of a leaf spot disease is spots on foliage. The spots will vary in size and color depending on the plant affected, the specific organism involved, and the stage of development. Spots are most often brownish, but may be tan or black. Concentric rings or dark margins are often present. Fungal bodies may appear as black dots in the spots, either in rings or in a central cluster. Over time, the spots may combine or enlarge to form blotches. Spots or blotches that are angular are generally referred to as anthracnose (see entry on “Anthracnose of Trees”) Leaves may yellow and drop prematurely.
Life Cycle
The organisms that cause leaf spots survive in fallen infected leaves and twigs. Some may remain in dead twigs on the tree. Most damage occurs in spring. During wet weather, spores may splash or be windblown onto newly emerging tender leaves where they germinate in the moisture and infect the leaf. Overhead watering can also provide prolonged wet periods that are ideal for spreading leaf spot diseases.
Integrated Pest Management Strategies
1. Live with the disease. Most trees tolerate leaf spots with little or no apparent damage. A tree affected early in the year will re-leaf and the new leaves may not be affected. Only if defoliation occurs three or more years in a row will most established plants be adversely affected.
2. Remove infected leaves and dead twigs. Raking up and disposing of infected leaves as they drop and pruning out dead twigs can help control the disease by removing spores that can reinfect the new leaves. This is not a cure but may help limit infection by reducing the total amount of inoculum.
3. Keep foliage dry. Avoid overhead watering. Use soaker hoses or water early in the day so the foliage can dry off before night. Watering can also spread the disease by splashing. Pruning plants to allow for good air circulation and reducing crowding will also help keep the foliage dry.
4. Keep plants healthy. Since most plants can tolerate some defoliation, keep them in good health so they can rebound quickly. Avoid over fertilizing by testing the soil first. Abundant, young, tender growth is very susceptible to attack by disease and insects. Overuse of nitrogen can cause an abundance of succulent growth.
5. Use fungicides if needed. In rare cases of severe infection and where the size and value of plants make it practicable, applications of fungicides may be helpful. Sprays will not cure infected leaves. Therefore, once the damage is noticed, spraying may have limited value. Spraying generally needs to be started as buds break in the spring and repeated at 10–14 day intervals. Recommendations will vary by disease and fungicide used. Have the disease identified before purchasing a control product.
6. Replace the plant. Though a drastic measure, many gardeners find it less bother and more rewarding to replace a plant that is continually plagued with leaf spot diseases. Either replace with a different kind of plant or a variety that is more resistant or tolerant of disease. A nursery can help you in your selection.
Symptoms and Diagnosis
The chief symptom of a leaf spot disease is spots on foliage. The spots will vary in size and color depending on the plant affected, the specific organism involved, and the stage of development. Spots are most often brownish, but may be tan or black. Concentric rings or dark margins are often present. Fungal bodies may appear as black dots in the spots, either in rings or in a central cluster. Over time, the spots may combine or enlarge to form blotches. Spots or blotches that are angular are generally referred to as anthracnose (see entry on “Anthracnose of Trees”) Leaves may yellow and drop prematurely.
Life Cycle
The organisms that cause leaf spots survive in fallen infected leaves and twigs. Some may remain in dead twigs on the tree. Most damage occurs in spring. During wet weather, spores may splash or be windblown onto newly emerging tender leaves where they germinate in the moisture and infect the leaf. Overhead watering can also provide prolonged wet periods that are ideal for spreading leaf spot diseases.
Integrated Pest Management Strategies
1. Live with the disease. Most trees tolerate leaf spots with little or no apparent damage. A tree affected early in the year will re-leaf and the new leaves may not be affected. Only if defoliation occurs three or more years in a row will most established plants be adversely affected.
2. Remove infected leaves and dead twigs. Raking up and disposing of infected leaves as they drop and pruning out dead twigs can help control the disease by removing spores that can reinfect the new leaves. This is not a cure but may help limit infection by reducing the total amount of inoculum.
3. Keep foliage dry. Avoid overhead watering. Use soaker hoses or water early in the day so the foliage can dry off before night. Watering can also spread the disease by splashing. Pruning plants to allow for good air circulation and reducing crowding will also help keep the foliage dry.
4. Keep plants healthy. Since most plants can tolerate some defoliation, keep them in good health so they can rebound quickly. Avoid over fertilizing by testing the soil first. Abundant, young, tender growth is very susceptible to attack by disease and insects. Overuse of nitrogen can cause an abundance of succulent growth.
5. Use fungicides if needed. In rare cases of severe infection and where the size and value of plants make it practicable, applications of fungicides may be helpful. Sprays will not cure infected leaves. Therefore, once the damage is noticed, spraying may have limited value. Spraying generally needs to be started as buds break in the spring and repeated at 10–14 day intervals. Recommendations will vary by disease and fungicide used. Have the disease identified before purchasing a control product.
6. Replace the plant. Though a drastic measure, many gardeners find it less bother and more rewarding to replace a plant that is continually plagued with leaf spot diseases. Either replace with a different kind of plant or a variety that is more resistant or tolerant of disease. A nursery can help you in your selection.
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文章
Dummer. ゛☀
2017年09月19日
Bacterial wetwood, also known as slime flux, is caused by an infection of one or more of several bacteria. It results in a water-soaked, oozing or bleeding condition of wood, which occurs in the trunk, branches and roots of shade and ornamental trees. It is normally not serious in most trees but is a chronic disease, which causes concern and can contribute to a general decline in tree vigor over time. Trees most susceptible to the disease include: elms, apple, crabapple, London plane, redbud, aspen, dogwood, magnolia, Russian olive, beech, fir, maple, sour gum, birches, hemlock, mountain ash, sycamore, boxelder, hickory, mulberry, sweet gum, butternut, horse chestnut, oaks, tulip tree, cottonwood, linden, pines, black locust, poplar, willow and walnut.
Symptoms and Diagnosis
Symptoms vary with geographical location suggesting that the environment influences disease development. Trees in the western United States show more variability in internal disease development with much less bleeding and symptom expression than trees in the East and Midwest. Wetwood appears internally in the trunk and large limbs as a dark brown-black water-soaked area when the area is sectioned. The first external sign of wetwood is usually bubbling and seepage from wounded tissue in V-shaped branch crotches, wounds made by removal of branches, injection holes and trunk cracks. Insects are often attracted to the ooze on which they feed but there is not any evidence that these insects cause damage or transmit the bacteria but it is believed that some wood boring insects such as beetles may transmit the disease.
Life Cycle
Organisms, most commonly bacteria, infect the tree deep in the tissue and start a process of fermentation. The resulting pressure (up to 60 psi) forces the bacterial ooze out cracks, branch stubs and pruning cuts. This ooze discolors bark, kills the cambium near the cut preventing proper callusing of wounds and kills grass and other plants on which it drips. Bacterial wetwood is noticed externally when it exudes slime and leaves a stain on the bark. Wilting of foliage is common in young trees; old trees are more likely to develop a general decline in vigor or branch dieback in the upper crown.
Integrated Pest Management Strategies
1. There is no cure or preventive treatment to avoid infection and development of bacterial wetwood. The following strategies may help.
2. Fertilization. Fertilize stressed trees to stimulate vigorous growth and lessen the severity of the disease but refrain from over fertilizing healthy vigorous trees as this may increase their susceptibility to the disorder.
3. Pruning. Remove any dead and weak branches. Promptly remove any loose or diseased bark around the area and make a clean cut arround wounds to facilitate healing. It is advided to disinfect tools with 70% rubbing alcohol before pruning a tree.
Inserting a drainage tube to drain the area is not recommended. Insertion of a drainage tube can spread the disease and result in more harm than good.
Symptoms and Diagnosis
Symptoms vary with geographical location suggesting that the environment influences disease development. Trees in the western United States show more variability in internal disease development with much less bleeding and symptom expression than trees in the East and Midwest. Wetwood appears internally in the trunk and large limbs as a dark brown-black water-soaked area when the area is sectioned. The first external sign of wetwood is usually bubbling and seepage from wounded tissue in V-shaped branch crotches, wounds made by removal of branches, injection holes and trunk cracks. Insects are often attracted to the ooze on which they feed but there is not any evidence that these insects cause damage or transmit the bacteria but it is believed that some wood boring insects such as beetles may transmit the disease.
Life Cycle
Organisms, most commonly bacteria, infect the tree deep in the tissue and start a process of fermentation. The resulting pressure (up to 60 psi) forces the bacterial ooze out cracks, branch stubs and pruning cuts. This ooze discolors bark, kills the cambium near the cut preventing proper callusing of wounds and kills grass and other plants on which it drips. Bacterial wetwood is noticed externally when it exudes slime and leaves a stain on the bark. Wilting of foliage is common in young trees; old trees are more likely to develop a general decline in vigor or branch dieback in the upper crown.
Integrated Pest Management Strategies
1. There is no cure or preventive treatment to avoid infection and development of bacterial wetwood. The following strategies may help.
2. Fertilization. Fertilize stressed trees to stimulate vigorous growth and lessen the severity of the disease but refrain from over fertilizing healthy vigorous trees as this may increase their susceptibility to the disorder.
3. Pruning. Remove any dead and weak branches. Promptly remove any loose or diseased bark around the area and make a clean cut arround wounds to facilitate healing. It is advided to disinfect tools with 70% rubbing alcohol before pruning a tree.
Inserting a drainage tube to drain the area is not recommended. Insertion of a drainage tube can spread the disease and result in more harm than good.
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文章
Dummer. ゛☀
2017年09月19日
Bacterial leaf scorch (BLS) is a systemic disease caused by the bacterium Xylella fastidiosa, which invades the xylem (water and nutrient conducting tissues) of susceptible trees. It is most commonly seen in pin, red, shingle, bur, and white oaks, but can also affect elm, oak, sycamore, mulberry, sweetgum, sugar maple, and red maple. Xylem-feeding leafhoppers and spittlebugs spread the bacterium from tree to tree. Transmission between trees through root grafts has also been reported. There is no cure for this disease; it is chronic and potentially fatal.
Symptoms and Diagnosis
The first noticeable symptom is premature browning of leaves in mid-summer. Symptoms worsen throughout late summer and fall. Leaf margins turn brown, beginning with the older leaves and moving outward, spreading to leaves toward the branch tip. In most, but not all infected trees, browned, dead areas of the leaf are separated from green tissue by a narrow yellow border. The browned leaves may drop from the tree. Infected trees leaf-out normally the following year, with leaves on a few more branches turning prematurely brown in late summer. Symptoms become progressively worse over a period of 3 to 8 years, until the entire tree turns brown prematurely. The lack of green, chlorophyll producing leaves year after year leads to twig, branch, and limb death due to continual defoliation.
Bacterial leaf scorch can easily be mistaken for oak wilt or Dutch elm disease, except for the following:
The cycle of bacterial leaf scorch repeats and becomes worse over a long period of time. Oak wilt and Dutch elm disease are both capable of killing susceptible trees within a matter of months.
There is no streaking of the sapwood with bacterial leaf scorch.
In bacterial leaf scorch, the leaf browning develops from the leaf edges and works toward the mid-vein, whereas browning tends to happen in a more overall, uniform manner with oak wilt and Dutch elm disease.
Bacterial leaf scorch can also be mistaken for drought and heat stress. However, damage by bacterial leaf scorch begins in old leaves and spreads to the branch tips, with browning around the leaf edges. Damage due to environmental stresses tends to cause overall browning to the canopy and to individual leaves. Trees tend to react to environmental stress soon after damaging conditions occur whereas bacterial leaf scorch is unique in its timing. Leaf browning is generally not noticed until mid-summer and intensifies through late summer and fall.
The only way to confirm the diagnosis of bacterial leaf scorch is through laboratory analysis. This can be done by sending a sample to the MU Extension Plant Diagnostic Clinic. The best time to test for the presence of this disease is in late summer or early fall, when the bacteria count is at its highest.
Life Cycle
Infected leafhoppers and spittlebugs feed on the succulent, terminal shoots of susceptible host trees, transmitting the bacteria. Xylem vessels become clogged with bacterium as it travels within, multiplying and infecting other parts of the tree. There are no viable control options for the insect vectors. The cold-sensitive bacteria overwinter in protected areas within the xylem of the tree, and their populations begin to climb again as the next growing season progresses.
Integrated Pest Management Strategies
1. Maintain plant vigor. There is no cure for the disease. Keeping susceptible trees healthy and thriving can help them resist infection and survive longer once they are infected.
2. Practice good sanitation. Branches that have died due to bacterial leaf scorch should be routinely removed. Infected trees that are in a severe state of decline should also be removed. Disinfect pruning tools with a 10% bleach solution between pruning cuts.
3. Plant resistant species. In areas where bacterial leaf scorch has occurred, avoid planting highly susceptible trees.
4. Antibiotic injections. Oxytetracycline root flare injections applied in spring can reduce bacterium levels and delay symptoms by a couple of weeks. They are expensive, need to be reapplied each year, and possible damage resulting from long-term use is unknown. A certified arborist should be contacted if you are considering injections.
Symptoms and Diagnosis
The first noticeable symptom is premature browning of leaves in mid-summer. Symptoms worsen throughout late summer and fall. Leaf margins turn brown, beginning with the older leaves and moving outward, spreading to leaves toward the branch tip. In most, but not all infected trees, browned, dead areas of the leaf are separated from green tissue by a narrow yellow border. The browned leaves may drop from the tree. Infected trees leaf-out normally the following year, with leaves on a few more branches turning prematurely brown in late summer. Symptoms become progressively worse over a period of 3 to 8 years, until the entire tree turns brown prematurely. The lack of green, chlorophyll producing leaves year after year leads to twig, branch, and limb death due to continual defoliation.
Bacterial leaf scorch can easily be mistaken for oak wilt or Dutch elm disease, except for the following:
The cycle of bacterial leaf scorch repeats and becomes worse over a long period of time. Oak wilt and Dutch elm disease are both capable of killing susceptible trees within a matter of months.
There is no streaking of the sapwood with bacterial leaf scorch.
In bacterial leaf scorch, the leaf browning develops from the leaf edges and works toward the mid-vein, whereas browning tends to happen in a more overall, uniform manner with oak wilt and Dutch elm disease.
Bacterial leaf scorch can also be mistaken for drought and heat stress. However, damage by bacterial leaf scorch begins in old leaves and spreads to the branch tips, with browning around the leaf edges. Damage due to environmental stresses tends to cause overall browning to the canopy and to individual leaves. Trees tend to react to environmental stress soon after damaging conditions occur whereas bacterial leaf scorch is unique in its timing. Leaf browning is generally not noticed until mid-summer and intensifies through late summer and fall.
The only way to confirm the diagnosis of bacterial leaf scorch is through laboratory analysis. This can be done by sending a sample to the MU Extension Plant Diagnostic Clinic. The best time to test for the presence of this disease is in late summer or early fall, when the bacteria count is at its highest.
Life Cycle
Infected leafhoppers and spittlebugs feed on the succulent, terminal shoots of susceptible host trees, transmitting the bacteria. Xylem vessels become clogged with bacterium as it travels within, multiplying and infecting other parts of the tree. There are no viable control options for the insect vectors. The cold-sensitive bacteria overwinter in protected areas within the xylem of the tree, and their populations begin to climb again as the next growing season progresses.
Integrated Pest Management Strategies
1. Maintain plant vigor. There is no cure for the disease. Keeping susceptible trees healthy and thriving can help them resist infection and survive longer once they are infected.
2. Practice good sanitation. Branches that have died due to bacterial leaf scorch should be routinely removed. Infected trees that are in a severe state of decline should also be removed. Disinfect pruning tools with a 10% bleach solution between pruning cuts.
3. Plant resistant species. In areas where bacterial leaf scorch has occurred, avoid planting highly susceptible trees.
4. Antibiotic injections. Oxytetracycline root flare injections applied in spring can reduce bacterium levels and delay symptoms by a couple of weeks. They are expensive, need to be reapplied each year, and possible damage resulting from long-term use is unknown. A certified arborist should be contacted if you are considering injections.
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Dummer. ゛☀
2017年09月19日
Anthracnose is a group of related fungal leaf and stem diseases that infect shade trees. Maple anthracnose is not the same disease as oak anthracnose, although the symptoms of these diseases may be quite similar. Anthracnose diseases generally infect the leaf veins and cause death of the vein and surrounding tissue. Control of anthracnose diseases follows the same procedure for all shade trees affected. The disease does not cause the death of the host but may reduce growth over successive seasons of complete defoliation.
Symptoms and Diagnosis
Irregular, light brown spots of dead tissue develop along the veins of the leaves. Affected plants may have the appearance of being sun-scorched. Sunken cankers containing fungal spores develop on infected twigs of some trees, such as sycamore.
Life Cycle
Anthracnose fungi overwinter on fallen leaves and twigs that were infected the proceeding year. Infection is favored by cool, moist weather in the spring of the year. Infection can occur on the vulnerable young leaves when there is a film of water on the leaf surface. Infection is typically more severe on the lower third of the tree, where the humidity is the highest.
Integrated Pest Management Strategies
1. Collect and destroy infected leaves as they fall. Infected leaves and twigs that remain in the vicinity are a source of spores for new infections in the spring.
2. Prune out dead branches. Be sure to clean all garden tools to avoid the spread of the disease. A 1–part bleach to 9–part water solution can be used to dip tools into between cuts.
3. Promote air circulation. Thin out excessive twig and branch growth. This will reduce the period of time that leaves are wet and vulnerable to inoculation.
4. Keep trees growing vigorously. Supply 1–2 inches of water weekly only during dry periods. Fertilize early in the spring or in late fall.
5. Spray with a fungicide when leaves are beginning to enlarge from the buds. Reapply at 7–10 day intervals for two or three more times. Fungicide sprays are most appropriate for younger, newly transplanted trees that may not be able to withstand defoliation. The available fungicides are preventive, not curative, and therefore, must be applied before spotting occurs. Commonly used products include copper, chlorothalonil (Daconil), captan, ferbam, mancozeb, maneb, and thiram. Your pesticide choice should be based on the particular problem you are seeking to control. Consult an arborist for difficult situations and where power equipment is required.
Symptoms and Diagnosis
Irregular, light brown spots of dead tissue develop along the veins of the leaves. Affected plants may have the appearance of being sun-scorched. Sunken cankers containing fungal spores develop on infected twigs of some trees, such as sycamore.
Life Cycle
Anthracnose fungi overwinter on fallen leaves and twigs that were infected the proceeding year. Infection is favored by cool, moist weather in the spring of the year. Infection can occur on the vulnerable young leaves when there is a film of water on the leaf surface. Infection is typically more severe on the lower third of the tree, where the humidity is the highest.
Integrated Pest Management Strategies
1. Collect and destroy infected leaves as they fall. Infected leaves and twigs that remain in the vicinity are a source of spores for new infections in the spring.
2. Prune out dead branches. Be sure to clean all garden tools to avoid the spread of the disease. A 1–part bleach to 9–part water solution can be used to dip tools into between cuts.
3. Promote air circulation. Thin out excessive twig and branch growth. This will reduce the period of time that leaves are wet and vulnerable to inoculation.
4. Keep trees growing vigorously. Supply 1–2 inches of water weekly only during dry periods. Fertilize early in the spring or in late fall.
5. Spray with a fungicide when leaves are beginning to enlarge from the buds. Reapply at 7–10 day intervals for two or three more times. Fungicide sprays are most appropriate for younger, newly transplanted trees that may not be able to withstand defoliation. The available fungicides are preventive, not curative, and therefore, must be applied before spotting occurs. Commonly used products include copper, chlorothalonil (Daconil), captan, ferbam, mancozeb, maneb, and thiram. Your pesticide choice should be based on the particular problem you are seeking to control. Consult an arborist for difficult situations and where power equipment is required.
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Dummer. ゛☀
2017年09月19日
Scale insects are common pests of many trees and shrubs. There are two general types of scale– armored scale and soft scales. A few of the species that fall into the armored scales are oystershell scale, San Jose scale, euonymus scale, and pine needle scale. Some soft scales are cottony maple scale, magnolia scale, and tuliptree scale. Scale coverings range in size, shape, and color depending on species.
Symptoms and Diagnosis
Trees heavily infested with armored scale often look water-stressed. Leaves turn yellow and drop, twigs and limbs may die, and the bark cracks and gums. Armored scales can kill trees and must be controlled when their population gets too high.
Soft scales also reduce plant vigor, but usually not enough to kill the plant. The main problem soft scales cause is the large amounts of honeydew they produce, which can cover leaves and fruit and act as a growth medium for black, sooty mold. Honeydew also attracts ants, flies, wasps, and bees that can become a nuisance.
Scale are identified by their body covering, which normally appears as a colored raised area on the leaf or stem of the plant that can be flicked off with the point of a knife or a fingernail. They vary in size but are generally only about 1/8 inch long.
Life Cycle
The life cycle of each species of scale can vary depending on the season and species. Armored scales usually have several generations a year, while soft scales have a single generation.
Scale overwinters on leaves, needles, stems, or twigs of the infested plant under the covering (shell) it creates. Under the scale shell, the female lays eggs. In the spring, the eggs hatch and the unprotected larvae (crawlers) emerge from under the protective shell and begin feeding on their own. The actual date of emergence varies with each type of scale insect and the weather. New plants can be infested when crawlers walk or are blown by the wind to a nearby plant. After a few days, the crawlers of armored scales settle down permanently, molt (and lose their legs), and begin to form their covering. Soon winged adult males crawl out from beneath their cover and mate with covered females. Adult male scales are tiny, winged, and seldom seen. Soft scale crawlers move about the plant a little longer after hatching before they settle down at a permanent feeding site. Some soft scale species move around during their immature stages and retain their legs for life. Their covers may be smooth or cottony, but they are firmly attached to their bodies. Soft scale tends to be larger than armored scale. Mature scales never move once they firmly attach themselves to the plant.
Integrated Pest Management Strategies
1. Maintain plant vigor. Maintaining a healthy plant is the best way to prevent infection by diseases or attack by insects. This can be accomplished by proper care including watering, fertilizing, providing a well-draining soil medium, adequate lighting, and air movement.
2. Pruning. Prune out heavily infested shoots or limbs. This will reduce the population and foster growth of new un-infested shoots.
3. Manual. Remove scale manually by rubbing them off the plant using your hand or a toothbrush. In the case of houseplants, use a cotton swab and rubbing alcohol.
4. Biological. Natural enemies, such as the ladybird beetle (ladybug) and small parasitic wasps, help control many scale species. Inspect the scale for round exit holes made by the emerging adult parasites. Before applying any insecticides, check the plant for the presence of the natural enemies and make sure that they are not already reducing scale numbers. If pesticide treatment is deemed necessary, confine the treatment to only those plants infested.
5. Chemical control. Many scale species on deciduous trees can be effectively controlled with either a dormant spray of refined horticultural, superior-type oil or summer oil spray or both. Oils and insecticidal soaps work by smothering the insect, both adults and crawlers. Other insecticides registered for use include malathion, bifenthrin, imidacloprid and pyrethrins.
6. Timing. Broad spectrum insecticidal treatments are most effective when applied in the crawler stage. Monitor by using double-sided sticky tape around some branches of the tree. Crawlers appear as tiny, pale yellow specks ("fried eggs") on the tape.
7.Repeat. In the case of overlapping generations, where every stage of development occurs, two to four applications at ten-day intervals will be needed.
8. Directions. Read and follow label directions. Check to insure the type scale and the host plant are listed on the label before using any insecticide.
Symptoms and Diagnosis
Trees heavily infested with armored scale often look water-stressed. Leaves turn yellow and drop, twigs and limbs may die, and the bark cracks and gums. Armored scales can kill trees and must be controlled when their population gets too high.
Soft scales also reduce plant vigor, but usually not enough to kill the plant. The main problem soft scales cause is the large amounts of honeydew they produce, which can cover leaves and fruit and act as a growth medium for black, sooty mold. Honeydew also attracts ants, flies, wasps, and bees that can become a nuisance.
Scale are identified by their body covering, which normally appears as a colored raised area on the leaf or stem of the plant that can be flicked off with the point of a knife or a fingernail. They vary in size but are generally only about 1/8 inch long.
Life Cycle
The life cycle of each species of scale can vary depending on the season and species. Armored scales usually have several generations a year, while soft scales have a single generation.
Scale overwinters on leaves, needles, stems, or twigs of the infested plant under the covering (shell) it creates. Under the scale shell, the female lays eggs. In the spring, the eggs hatch and the unprotected larvae (crawlers) emerge from under the protective shell and begin feeding on their own. The actual date of emergence varies with each type of scale insect and the weather. New plants can be infested when crawlers walk or are blown by the wind to a nearby plant. After a few days, the crawlers of armored scales settle down permanently, molt (and lose their legs), and begin to form their covering. Soon winged adult males crawl out from beneath their cover and mate with covered females. Adult male scales are tiny, winged, and seldom seen. Soft scale crawlers move about the plant a little longer after hatching before they settle down at a permanent feeding site. Some soft scale species move around during their immature stages and retain their legs for life. Their covers may be smooth or cottony, but they are firmly attached to their bodies. Soft scale tends to be larger than armored scale. Mature scales never move once they firmly attach themselves to the plant.
Integrated Pest Management Strategies
1. Maintain plant vigor. Maintaining a healthy plant is the best way to prevent infection by diseases or attack by insects. This can be accomplished by proper care including watering, fertilizing, providing a well-draining soil medium, adequate lighting, and air movement.
2. Pruning. Prune out heavily infested shoots or limbs. This will reduce the population and foster growth of new un-infested shoots.
3. Manual. Remove scale manually by rubbing them off the plant using your hand or a toothbrush. In the case of houseplants, use a cotton swab and rubbing alcohol.
4. Biological. Natural enemies, such as the ladybird beetle (ladybug) and small parasitic wasps, help control many scale species. Inspect the scale for round exit holes made by the emerging adult parasites. Before applying any insecticides, check the plant for the presence of the natural enemies and make sure that they are not already reducing scale numbers. If pesticide treatment is deemed necessary, confine the treatment to only those plants infested.
5. Chemical control. Many scale species on deciduous trees can be effectively controlled with either a dormant spray of refined horticultural, superior-type oil or summer oil spray or both. Oils and insecticidal soaps work by smothering the insect, both adults and crawlers. Other insecticides registered for use include malathion, bifenthrin, imidacloprid and pyrethrins.
6. Timing. Broad spectrum insecticidal treatments are most effective when applied in the crawler stage. Monitor by using double-sided sticky tape around some branches of the tree. Crawlers appear as tiny, pale yellow specks ("fried eggs") on the tape.
7.Repeat. In the case of overlapping generations, where every stage of development occurs, two to four applications at ten-day intervals will be needed.
8. Directions. Read and follow label directions. Check to insure the type scale and the host plant are listed on the label before using any insecticide.
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文章
Dummer. ゛☀
2017年09月18日
Bagworms, Thyridopteryx ephemeraeformis, produce conspicuous spindle-shaped cocoons on trees and shrubs throughout the United States. Bagworms feed on over 128 plant species. The most commonly attacked plants are arborvitae, red cedar, and other juniper species. They will also feed on fir, maple, juneberry, buckeye, persimmon, ginkgo, honeylocust, larch, sweet gum, spruce, pine, sycamore, poplar, oak, locust, willow, and hemlock.
Symptoms and Diagnosis
The principle harm done by the insect is the destruction of foliage by the caterpillars. Plants usually are partially defoliated, weakened, and rendered unsightly. Complete defoliation can occur. The most notable sign of bagworm infestation is the presence of protective bags attached to a branch. The bags incorporate bits of twigs and leaves from the host plant. They are approximately 1 to 2 inches long and resemble Christmas tree ornaments hanging from the limbs.
Life Cycle
The adult female bagworm does not look like a moth and never leaves her bag. She is maggot-like in appearance, soft-bodied, and yellowish-white. A mated female lays between 500 and 1000 eggs within the bag, after which she dies. The eggs remain inside the bag throughout the winter until they hatch the following spring. There is one generation a year.
From late May to mid-June, bagworm larvae (caterpillars) begin emerging from the bags. Almost immediately after emerging, a larva starts to produce its own protective bag. The bag is constructed such that the larva's head and legs are free. This construction allows the larvae to move about the plant as it feeds on the foliage. As the larva grows, it increases the size of its bag. The full-grown larvae are about one inch long.
When a host plant becomes defoliated, the larvae will crawl off it with their bags and search for a new plant to feed upon. In mid-August, the mature larvae stop feeding and attach their bags to a twig. They close up the bag and pupate. By mid-September, the bagworm has completed its development, and adult males begin emerging from their bags. The male moth has a black, furry body and feathery antennae. The wings are almost transparent and have a span of about one inch.
Integrated Pest Management Strategies
1. Handpick the bags. The most economical method of controlling bagworms is to handpick the bags and destroy them. Some birds and insect predators feed on larvae, so light infestations on large, healthy plants are usually controlled by natural means. On large plants, monitor infestations before resorting to chemical sprays. If the problem doesn't get worse, spraying is not required.
2. Use biological controls. In spring, as soon as eggs hatch and the young emerge, spray with Bacillus thuringiensis (Bt). Bt is a bacterium that causes the larvae to become sick, stop feeding, and later die. In St. Louis, the eggs hatch in late May to mid-June, or about the time the cigar tree, Catalpa speciosa, is in full bloom.
3. Use chemical controls. Because bagworms form protective bags very early, contact insecticides, while useful, are less effective than stomach poisons. For best control, spray when insects are young. Chemical controls become less effective as the bagworm matures. Chemical controls include acephate (Orthene), cyfluthrin and spinosad.
Symptoms and Diagnosis
The principle harm done by the insect is the destruction of foliage by the caterpillars. Plants usually are partially defoliated, weakened, and rendered unsightly. Complete defoliation can occur. The most notable sign of bagworm infestation is the presence of protective bags attached to a branch. The bags incorporate bits of twigs and leaves from the host plant. They are approximately 1 to 2 inches long and resemble Christmas tree ornaments hanging from the limbs.
Life Cycle
The adult female bagworm does not look like a moth and never leaves her bag. She is maggot-like in appearance, soft-bodied, and yellowish-white. A mated female lays between 500 and 1000 eggs within the bag, after which she dies. The eggs remain inside the bag throughout the winter until they hatch the following spring. There is one generation a year.
From late May to mid-June, bagworm larvae (caterpillars) begin emerging from the bags. Almost immediately after emerging, a larva starts to produce its own protective bag. The bag is constructed such that the larva's head and legs are free. This construction allows the larvae to move about the plant as it feeds on the foliage. As the larva grows, it increases the size of its bag. The full-grown larvae are about one inch long.
When a host plant becomes defoliated, the larvae will crawl off it with their bags and search for a new plant to feed upon. In mid-August, the mature larvae stop feeding and attach their bags to a twig. They close up the bag and pupate. By mid-September, the bagworm has completed its development, and adult males begin emerging from their bags. The male moth has a black, furry body and feathery antennae. The wings are almost transparent and have a span of about one inch.
Integrated Pest Management Strategies
1. Handpick the bags. The most economical method of controlling bagworms is to handpick the bags and destroy them. Some birds and insect predators feed on larvae, so light infestations on large, healthy plants are usually controlled by natural means. On large plants, monitor infestations before resorting to chemical sprays. If the problem doesn't get worse, spraying is not required.
2. Use biological controls. In spring, as soon as eggs hatch and the young emerge, spray with Bacillus thuringiensis (Bt). Bt is a bacterium that causes the larvae to become sick, stop feeding, and later die. In St. Louis, the eggs hatch in late May to mid-June, or about the time the cigar tree, Catalpa speciosa, is in full bloom.
3. Use chemical controls. Because bagworms form protective bags very early, contact insecticides, while useful, are less effective than stomach poisons. For best control, spray when insects are young. Chemical controls become less effective as the bagworm matures. Chemical controls include acephate (Orthene), cyfluthrin and spinosad.
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Dummer. ゛☀
2017年09月18日
Sphaeropsis tip blight is caused by the fungus, Sphaeropsis sapinea (also known as Diplodia pinea). It is one of the most destructive fungal diseases of pine trees in the Midwest. It is most common on Austrian pine but can also damage Scotch pine (Scots pine), ponderosa, and mugo pine. If not controlled, over a period of years, it will weaken and perhaps kill the tree.
Symptoms and Diagnosis
Tip blight most commonly affects trees 13 or more years old that bear mature pine cones, but it can also affect younger trees. The most obvious symptom is the browning and stunting of the needles of the new growth. The needles are retained on the tree. Excess resin flow builds up on the dead twigs and needle bases. Small black pimples (pycnidia) about the size of fly specks are very noticeable on the bases of the browned needles, on the dead twigs, and on the cone scales. The pimples are the fruiting bodies of the fungus. Infection usually begins on the lower branches and moves up the tree. Sphaeropsis tip blight may be confused with pine tip moth damage. In the case of the latter, the fungal fruiting bodies will not be present, but moth larvae and tunneling in the shoots will be evident.
Life Cycle
Symptoms of tip dieback are most common in spring from April to mid-June when the young emerging needles are soft and tender. They are most vulnerable for the two weeks when the buds first open. Spores are released from the fruiting bodies (pycnidia) and are moved by splashing rain, wind, animals, and pruning equipment. They are dispersed throughout the year. Under very moist, humid conditions, the spores germinate and infect the needles. Once the fungus infects the needles, tissue is destroyed and shoots and needles are stunted. Infected second-year cones are a major source of inoculum. Infected cones are often observed on plants that show no other signs of infection. Latent infection is common and may be symptomless.
Integrated Pest Management Strategies
1. Keep trees healthy. Weakened trees are more susceptible to disease. Water during dry periods and fertilize according to soil test recommendations. Spores of Sphaeropsis sapinea are ever-present and can be found on the branches of most pine trees with the exception of white pine. Spores can infect without causing symptoms.
2. Use fungicidal sprays.Infection of new shoots may be reduced significantly with properly timed fungicidal sprays. Fixed copper or Bordeaux should be applied twice during the period when buds are opening. Apply in late April to early May, when the buds just begin to open. Repeat application in one to two weeks. Other pesticides registered for use include chlorothalonil (Daconil), mancozeb, and thiophanate methyl (Cleary 3336).
3. Replace with more resistant trees. When dead or dying trees are removed, replant with trees that are less susceptible to Sphaeropsis tip blight such as white pine, spruces, or junipers.
Symptoms and Diagnosis
Tip blight most commonly affects trees 13 or more years old that bear mature pine cones, but it can also affect younger trees. The most obvious symptom is the browning and stunting of the needles of the new growth. The needles are retained on the tree. Excess resin flow builds up on the dead twigs and needle bases. Small black pimples (pycnidia) about the size of fly specks are very noticeable on the bases of the browned needles, on the dead twigs, and on the cone scales. The pimples are the fruiting bodies of the fungus. Infection usually begins on the lower branches and moves up the tree. Sphaeropsis tip blight may be confused with pine tip moth damage. In the case of the latter, the fungal fruiting bodies will not be present, but moth larvae and tunneling in the shoots will be evident.
Life Cycle
Symptoms of tip dieback are most common in spring from April to mid-June when the young emerging needles are soft and tender. They are most vulnerable for the two weeks when the buds first open. Spores are released from the fruiting bodies (pycnidia) and are moved by splashing rain, wind, animals, and pruning equipment. They are dispersed throughout the year. Under very moist, humid conditions, the spores germinate and infect the needles. Once the fungus infects the needles, tissue is destroyed and shoots and needles are stunted. Infected second-year cones are a major source of inoculum. Infected cones are often observed on plants that show no other signs of infection. Latent infection is common and may be symptomless.
Integrated Pest Management Strategies
1. Keep trees healthy. Weakened trees are more susceptible to disease. Water during dry periods and fertilize according to soil test recommendations. Spores of Sphaeropsis sapinea are ever-present and can be found on the branches of most pine trees with the exception of white pine. Spores can infect without causing symptoms.
2. Use fungicidal sprays.Infection of new shoots may be reduced significantly with properly timed fungicidal sprays. Fixed copper or Bordeaux should be applied twice during the period when buds are opening. Apply in late April to early May, when the buds just begin to open. Repeat application in one to two weeks. Other pesticides registered for use include chlorothalonil (Daconil), mancozeb, and thiophanate methyl (Cleary 3336).
3. Replace with more resistant trees. When dead or dying trees are removed, replant with trees that are less susceptible to Sphaeropsis tip blight such as white pine, spruces, or junipers.
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Dummer. ゛☀
2017年09月18日
Decline of trees and shrubs can be described in two ways–gradual and sudden. Sudden decline can cause the death of a plant anywhere from a month to a couple of years. Gradual decline generally occurs over several years. It can sometimes be difficult to distinguish between the two, not noticing the decline until too late.
The sudden death of trees and shrubs can be brought on by a single, primary cause that kills an otherwise healthy plant. This might be the case with an aggressive pathogen like Dutch elm disease or white pine blister rust. With gradual decline, no one particular disease causes the plant to die. Instead, conditions weaken the plant to the point that secondary organisms are able to invade the stressed plant. Dieback and decline diseases are caused by the successive action of primary stress factor(s) followed by organisms of secondary action that can successfully attack only weakened trees. One may attribute the plant’s decline to these secondary organisms, but an experienced professional knows the problem lies deeper.
Factors that lead to decline are many. This includes adverse weather conditions, such as rapid changes in winter temperatures and late spring and early fall frosts, flooding or changes in the water table, drought, bark damage from lawn mower injury or weed eaters, frost cracks, or animal feeding. Injury can also occur from lawn weed killers or other chemicals, accumulated salt injury from road salt, environmental pollution, soil fertility, or girdled or restricted root development. Finally, leaf loss from insects or diseases and damage from construction around the tree because of soil fill, root pruning, or soil compaction from heavy equipment can also be causes. Working singly or together over several years, these stresses can eventually result in tree or shrub death. A good example leading to gradual decline might be root decline where symptoms observed in the aboveground parts of the plant usually begin in the root system. When trees and shrubs are under stress, physiological changes occur in the roots, allowing fungi to infect the tissue.
Removal of the stress factors is required to save the declining plant. In many cases, action may come too late or may be impractical to carry out.
Symptoms and Diagnosis
Symptoms usually develop slowly and may not be noticed immediately. Trees and shrubs exhibit an overall loss of vigor. Early symptoms might include premature fall coloration of leaves, late leaf emergence in spring, production of foliage in clumps, decrease in twig growth, dieback, death of tissues between the leaf veins, and premature leaf drop. Later symptoms might include sprouting from the trunk, heavy seed crop production, dieback of larger limbs and branches, and foliage noticeably smaller and lighter green (chlorotic). The foliage over the entire plant may also look thinner in decline conditions. These visible symptoms may not occur until the plant is severely stressed. In the autumn, clusters of mushrooms may form at the base of infected trees.
Wood-boring insects such as borers are also frequently associated with declining plants as they are attracted to weakened, stressed plants. Scale insects are also commonly found on stressed plants.
Integrated Pest Management Strategies
1. Location.Avoid placing plants in a stressful situation. Select species that are suited to the conditions of the planting location or modify the planting site to suit the requirements of the plant. This would include planting in a well-draining soil with the correct pH for the plant. Environmental conditions should also be considered, such as full sun for a sun-loving plant—not in the shade of another plant. Use warm weather plants in warm climates and moisture-loving plants in wet conditions.
2.Inspection. Prevention and early detection are the key to keeping trees and shrubs healthy. Inspect plants often and watch for symptoms of stress.
3. Planting. Do not crowd plants in restricted areas, such as close to sidewalks or streets, or place too many plants in an area that cannot support them.
4. On-going care. Water to reduce drought stress. Using a fertilizer like 5-10-5 that is high in phosphorus and low in nitrogen will stimulate root growth rather than shoot growth. Mulching over the root system will help prevent the loss of water, decrease compaction from rain, and keep the roots cool in the summer and warmer in the winter.
5. Pruning. Prune all dead and dying branches and no more than 10 to 20% of the remaining live branches at any one time. This should balance the foliage to the root system. If more pruning is necessary, complete this over 2–3 years.
6. Compaction. Compacted soil will cause a slow, sure death for many plants. Locate children’s play areas, dog runs, or car parking areas away from valuable trees and plantings. Core aerate compacted areas and around the drip line of trees. Change traffic patterns to reduce compacting the soil under trees.
7. Removal.Remove dead trees and shrubs and dispose of any infected material.
The sudden death of trees and shrubs can be brought on by a single, primary cause that kills an otherwise healthy plant. This might be the case with an aggressive pathogen like Dutch elm disease or white pine blister rust. With gradual decline, no one particular disease causes the plant to die. Instead, conditions weaken the plant to the point that secondary organisms are able to invade the stressed plant. Dieback and decline diseases are caused by the successive action of primary stress factor(s) followed by organisms of secondary action that can successfully attack only weakened trees. One may attribute the plant’s decline to these secondary organisms, but an experienced professional knows the problem lies deeper.
Factors that lead to decline are many. This includes adverse weather conditions, such as rapid changes in winter temperatures and late spring and early fall frosts, flooding or changes in the water table, drought, bark damage from lawn mower injury or weed eaters, frost cracks, or animal feeding. Injury can also occur from lawn weed killers or other chemicals, accumulated salt injury from road salt, environmental pollution, soil fertility, or girdled or restricted root development. Finally, leaf loss from insects or diseases and damage from construction around the tree because of soil fill, root pruning, or soil compaction from heavy equipment can also be causes. Working singly or together over several years, these stresses can eventually result in tree or shrub death. A good example leading to gradual decline might be root decline where symptoms observed in the aboveground parts of the plant usually begin in the root system. When trees and shrubs are under stress, physiological changes occur in the roots, allowing fungi to infect the tissue.
Removal of the stress factors is required to save the declining plant. In many cases, action may come too late or may be impractical to carry out.
Symptoms and Diagnosis
Symptoms usually develop slowly and may not be noticed immediately. Trees and shrubs exhibit an overall loss of vigor. Early symptoms might include premature fall coloration of leaves, late leaf emergence in spring, production of foliage in clumps, decrease in twig growth, dieback, death of tissues between the leaf veins, and premature leaf drop. Later symptoms might include sprouting from the trunk, heavy seed crop production, dieback of larger limbs and branches, and foliage noticeably smaller and lighter green (chlorotic). The foliage over the entire plant may also look thinner in decline conditions. These visible symptoms may not occur until the plant is severely stressed. In the autumn, clusters of mushrooms may form at the base of infected trees.
Wood-boring insects such as borers are also frequently associated with declining plants as they are attracted to weakened, stressed plants. Scale insects are also commonly found on stressed plants.
Integrated Pest Management Strategies
1. Location.Avoid placing plants in a stressful situation. Select species that are suited to the conditions of the planting location or modify the planting site to suit the requirements of the plant. This would include planting in a well-draining soil with the correct pH for the plant. Environmental conditions should also be considered, such as full sun for a sun-loving plant—not in the shade of another plant. Use warm weather plants in warm climates and moisture-loving plants in wet conditions.
2.Inspection. Prevention and early detection are the key to keeping trees and shrubs healthy. Inspect plants often and watch for symptoms of stress.
3. Planting. Do not crowd plants in restricted areas, such as close to sidewalks or streets, or place too many plants in an area that cannot support them.
4. On-going care. Water to reduce drought stress. Using a fertilizer like 5-10-5 that is high in phosphorus and low in nitrogen will stimulate root growth rather than shoot growth. Mulching over the root system will help prevent the loss of water, decrease compaction from rain, and keep the roots cool in the summer and warmer in the winter.
5. Pruning. Prune all dead and dying branches and no more than 10 to 20% of the remaining live branches at any one time. This should balance the foliage to the root system. If more pruning is necessary, complete this over 2–3 years.
6. Compaction. Compacted soil will cause a slow, sure death for many plants. Locate children’s play areas, dog runs, or car parking areas away from valuable trees and plantings. Core aerate compacted areas and around the drip line of trees. Change traffic patterns to reduce compacting the soil under trees.
7. Removal.Remove dead trees and shrubs and dispose of any infected material.
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文章
Dummer. ゛☀
2017年09月18日
Poison ivy, Toxicodendron radicans, is usually a vine twining on trees and occasionally an upright bush if there is no support. Each leaf is made up of three leaflets more or less notched at the edges. Two of the leaflets form a pair on opposite sides of the leafstalk, while the third leaflet stands by itself at the tip of the leafstalk. Small greenish flowers grow in bunches attached to the main stem close to the point where each leaf joins it. Later in the season, clusters of poisonous, berry-like drupes form. They are a dirty yellowish-white, waxy berry similar to mistletoe. The leaves are red in early spring becoming shiny green in summer and then turning red or orange in autumn.
Integrated Pest Management Strategies
1. Pull small plants. If only a few small plants are found, pull and dispose of the plants using rubber gloves and arm protection. Avoid touching the leaves. Dispose of the plants in a plastic bag so they will not be touched by others. All parts of the plant are toxic. NEVER BURN THE PLANTS. The fumes are as toxic as touching the plant and worse if inhaled.
2. Use herbicides. For small areas, poison ivy killers available in aerosol cans may be a good choice. They are effective and convenient but are too expensive for treating large areas.
Another option is to use glyphosate (Roundup, Kleenup). Spray the leaves of actively growing plants taking care to protect nearby desirable plants from spray drift which can damage or kill them. Leaves can also be selectively "painted" with the solution using a brush or wiped on plants using a disposable cotton rag. Use rubber gloves approved for use with garden chemicals and avoid contact of the herbicide with skin and eyes.
A combination of 2,4-D and Banvel is also effective, but use 2,4-D with care as nearby plants may be sensitive to the drift. To kill the roots of large plants, cut the stem at soil level. Then paint the cut with undiluted 2,4-D. Mound soil over the treated stub. Amino triazole (Amitrol-T, Amino Triazole 90, and Weedazol) is also highly effective and safe to use. Available as a liquid or wettable powder, it should be applied during periods of rapid plant growth. Thorough coverage of the foliage is essential.
3.Use biological controls. Sheep and goats will eat poison ivy. Tether them in areas where you need poison ivy cleared. Not all municipalities or neighbors may welcome this control measure.
Integrated Pest Management Strategies
1. Pull small plants. If only a few small plants are found, pull and dispose of the plants using rubber gloves and arm protection. Avoid touching the leaves. Dispose of the plants in a plastic bag so they will not be touched by others. All parts of the plant are toxic. NEVER BURN THE PLANTS. The fumes are as toxic as touching the plant and worse if inhaled.
2. Use herbicides. For small areas, poison ivy killers available in aerosol cans may be a good choice. They are effective and convenient but are too expensive for treating large areas.
Another option is to use glyphosate (Roundup, Kleenup). Spray the leaves of actively growing plants taking care to protect nearby desirable plants from spray drift which can damage or kill them. Leaves can also be selectively "painted" with the solution using a brush or wiped on plants using a disposable cotton rag. Use rubber gloves approved for use with garden chemicals and avoid contact of the herbicide with skin and eyes.
A combination of 2,4-D and Banvel is also effective, but use 2,4-D with care as nearby plants may be sensitive to the drift. To kill the roots of large plants, cut the stem at soil level. Then paint the cut with undiluted 2,4-D. Mound soil over the treated stub. Amino triazole (Amitrol-T, Amino Triazole 90, and Weedazol) is also highly effective and safe to use. Available as a liquid or wettable powder, it should be applied during periods of rapid plant growth. Thorough coverage of the foliage is essential.
3.Use biological controls. Sheep and goats will eat poison ivy. Tether them in areas where you need poison ivy cleared. Not all municipalities or neighbors may welcome this control measure.
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文章
Dummer. ゛☀
2017年09月17日
Plum curculio, a snout beetle, is an important pest on stone fruits like plums, cherries, and peaches. Plum curculio is one of the most serious pests of peach trees; they lay eggs within the fruit and both adults and larvae feed on the fruit, causing brown rot of the fruit. On apples, plum curculio is considered the second most damaging pest after codling moth.
Symptoms and Diagnosis
Plum curculio beetles, Conotrachelus nenuphar, can be found on plum, cherry, peach, and apple trees, less commonly on nectarine and pear trees. Fruit may fall prematurely, in late May and June. The skin of infected fruit has small crescent-shaped blemishes that eventually become swollen and knotted. Upon closer examination, larvae may be seen feeding near the blemishes. Infested fruit is often hard and misshapen. The larvae create holes in the fruit skin when they leave the fruit to pupate. These holes are clean-cut and free of frass or webbing.
Life Cycle
Plum curculio beetles are dark brown, about 1/4 inch long, and have a prominent snout, measuring about 1/3 the length of their bodies. They have four characteristic humps on their wing covers. Adults may overwinter in the soil or in hedgerows near host trees. These adults emerge from their overwintering sites to feed on trees in early spring. Females lay eggs within the fruit. The larvae that emerge from the developing fruit have grayish-white, worm-like bodies with brown heads and can be seen on infested trees in late summer. Larvae may feed on the fruit for 2–3 weeks before they burrow into the ground to pupate. Adults emerge in mid- to latesummer to cause more feeding damage on mature fruit before they overwinter.
Integrated Pest Management Strategies
1. Shake infested trees. In backyards with only a handful of infested trees, plum curculios may be shaken out of infested trees. This technique works best early in the day when the beetles are sluggish. Lay paper or cloth underneath the trees to collect the beetles. Destroy the collected beetles.
2. Clean up fallen fruit in which eggs or larvae may be developing.
3. Cultivate the soil surrounding infested trees in late spring or early summer to destroy pupating larvae that may have fallen to the ground with the fruit or pupae that may be developing in burrows in the ground.
4. Apply insecticides when populations of adult beetles are severe. Apply carbaryl (Sevin) spray to curb feeding damage and prevent beetles from laying eggs. It is important to delay application of the pesticide until after flower petals drop to avoid harming pollinating insects. Reapply pesticides two more times, at 10–14 day intervals. Other pesticides registered for use include azadirachtin (Bio-Neem, Margosan-O), Beauvaria bassiana, malathion, and pyrethrins.
Symptoms and Diagnosis
Plum curculio beetles, Conotrachelus nenuphar, can be found on plum, cherry, peach, and apple trees, less commonly on nectarine and pear trees. Fruit may fall prematurely, in late May and June. The skin of infected fruit has small crescent-shaped blemishes that eventually become swollen and knotted. Upon closer examination, larvae may be seen feeding near the blemishes. Infested fruit is often hard and misshapen. The larvae create holes in the fruit skin when they leave the fruit to pupate. These holes are clean-cut and free of frass or webbing.
Life Cycle
Plum curculio beetles are dark brown, about 1/4 inch long, and have a prominent snout, measuring about 1/3 the length of their bodies. They have four characteristic humps on their wing covers. Adults may overwinter in the soil or in hedgerows near host trees. These adults emerge from their overwintering sites to feed on trees in early spring. Females lay eggs within the fruit. The larvae that emerge from the developing fruit have grayish-white, worm-like bodies with brown heads and can be seen on infested trees in late summer. Larvae may feed on the fruit for 2–3 weeks before they burrow into the ground to pupate. Adults emerge in mid- to latesummer to cause more feeding damage on mature fruit before they overwinter.
Integrated Pest Management Strategies
1. Shake infested trees. In backyards with only a handful of infested trees, plum curculios may be shaken out of infested trees. This technique works best early in the day when the beetles are sluggish. Lay paper or cloth underneath the trees to collect the beetles. Destroy the collected beetles.
2. Clean up fallen fruit in which eggs or larvae may be developing.
3. Cultivate the soil surrounding infested trees in late spring or early summer to destroy pupating larvae that may have fallen to the ground with the fruit or pupae that may be developing in burrows in the ground.
4. Apply insecticides when populations of adult beetles are severe. Apply carbaryl (Sevin) spray to curb feeding damage and prevent beetles from laying eggs. It is important to delay application of the pesticide until after flower petals drop to avoid harming pollinating insects. Reapply pesticides two more times, at 10–14 day intervals. Other pesticides registered for use include azadirachtin (Bio-Neem, Margosan-O), Beauvaria bassiana, malathion, and pyrethrins.
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文章
Dummer. ゛☀
2017年09月17日
The fall webworm, Hyphantria cunea, is a general feeder on nearly all trees except conifers. While this native North American insect attacks over 100 different tree species, it tends to prefer mulberry, walnut, hickory, elm, sweetgum, poplar, willow, oak, linden, ash, apple, and other fruit trees. The insect makes webs at branch tips and is harmful mainly to the beauty of the host. It is considered to be more of a nuisance than a threat to the health of the tree.
Symptoms and Diagnosis
A distinctive web of silk, containing many caterpillars, is constructed around leaves at branch ends. Each "nest" may contain hundreds of larvae that feed together for a while. By late summer, the unsightly nest may measure three feet across and, in addition to the growing larvae, contains excrement, dried leaf fragments, and cast skins. An unusual characteristic of fall webworm caterpillars is that if alarmed, all the caterpillars in a nest make jerking movements in unison. It is thought that this is a potential defensive mechanism to startle and deter predators.
Another tent-forming caterpillar is the eastern tent caterpillar, Malacosoma americanum. However, eastern tent caterpillars make webbed silk nests in a fork of a branch or tree trunk and leave the nest to feed. Fall webworm caterpillars have nests at branch tips and feed inside the webbing.
Life Cycle
In late spring or early summer, adults emerge from overwintering pupal cases and lay hair-covered masses of several hundred eggs on the underside of leaves. The larvae that emerge can be either yellowish green with a black head or tan with a red head. Both color forms have many long, gray hairs and pairs of wart-like black spots running down their backs. Once feeding begins, the larvae congregate in masses and produce the silky web that surrounds the entire colony. Larvae feed inside the web and expand it as they grow. Larvae stay in the colony until their last molt after which they may be found crawling anywhere on the host plant. The larvae crawl to a protected place to spin a flimsy cocoon and pupate. The adults emerging from pupation have two color forms: either all white or white with black spots. There are two generations a year.
Integrated Pest Management Strategies
1. Live with the problem and let nature take its course. Hosts are seldom seriously harmed because defoliation usually occurs later in summer rather than during a period of active growth and not enough terminal growth is consumed to affect tree growth. In addition, more than 75 natural enemies parasitize and prey on the fall webworm.
2. Prune out webs. Branches that have active webs ("nests") may be cut out and destroyed. Webs are always on branch ends and are easier to remove when they are small. Pole pruners are helpful for reaching into trees.
3. Apply insecticidal sprays. If chemical control is truly necessary, treatment is recommended when webs first appear. This is because the smaller caterpillars are more susceptible to insecticides and, secondly, the webbed nests are somewhat waterproof and can be difficult to penetrate with sprays. The microbial insecticide Bt (Bacillus thuringiensis) is available as Dipel or Thuricide and can be used on the small caterpillars. Other pesticides registered for use include acephate (Orthene), carbaryl (Sevin), pyrethrins and spinosad.
Symptoms and Diagnosis
A distinctive web of silk, containing many caterpillars, is constructed around leaves at branch ends. Each "nest" may contain hundreds of larvae that feed together for a while. By late summer, the unsightly nest may measure three feet across and, in addition to the growing larvae, contains excrement, dried leaf fragments, and cast skins. An unusual characteristic of fall webworm caterpillars is that if alarmed, all the caterpillars in a nest make jerking movements in unison. It is thought that this is a potential defensive mechanism to startle and deter predators.
Another tent-forming caterpillar is the eastern tent caterpillar, Malacosoma americanum. However, eastern tent caterpillars make webbed silk nests in a fork of a branch or tree trunk and leave the nest to feed. Fall webworm caterpillars have nests at branch tips and feed inside the webbing.
Life Cycle
In late spring or early summer, adults emerge from overwintering pupal cases and lay hair-covered masses of several hundred eggs on the underside of leaves. The larvae that emerge can be either yellowish green with a black head or tan with a red head. Both color forms have many long, gray hairs and pairs of wart-like black spots running down their backs. Once feeding begins, the larvae congregate in masses and produce the silky web that surrounds the entire colony. Larvae feed inside the web and expand it as they grow. Larvae stay in the colony until their last molt after which they may be found crawling anywhere on the host plant. The larvae crawl to a protected place to spin a flimsy cocoon and pupate. The adults emerging from pupation have two color forms: either all white or white with black spots. There are two generations a year.
Integrated Pest Management Strategies
1. Live with the problem and let nature take its course. Hosts are seldom seriously harmed because defoliation usually occurs later in summer rather than during a period of active growth and not enough terminal growth is consumed to affect tree growth. In addition, more than 75 natural enemies parasitize and prey on the fall webworm.
2. Prune out webs. Branches that have active webs ("nests") may be cut out and destroyed. Webs are always on branch ends and are easier to remove when they are small. Pole pruners are helpful for reaching into trees.
3. Apply insecticidal sprays. If chemical control is truly necessary, treatment is recommended when webs first appear. This is because the smaller caterpillars are more susceptible to insecticides and, secondly, the webbed nests are somewhat waterproof and can be difficult to penetrate with sprays. The microbial insecticide Bt (Bacillus thuringiensis) is available as Dipel or Thuricide and can be used on the small caterpillars. Other pesticides registered for use include acephate (Orthene), carbaryl (Sevin), pyrethrins and spinosad.
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文章
Dummer. ゛☀
2017年09月17日
The two most destructive species of cankerworms (a kind of inchworm) in the St. Louis area are the fall cankerworm and the spring cankerworm, both of which feed in the spring. They attack many different species of trees and shrubs.
Symptoms and Diagnosis
Leaves are chewed. Complete defoliation and crop loss may occur; or after repeated damage, less and less fruit is produced until little, if any, fruit matures. Damage is first evident in the early spring or summer after trees have fully leafed out. This is about the time that larvae of both species emerge and begin to feed.
Life Cycle
Cankerworms are small caterpillars, only getting up to an inch long. Adult males are small, gray moths with a wingspan reaching only 1 inch long. The females of both species are wingless.
FALL CANKERWORM: The adult fall cankerworm, Alsophila pometaria, emerges from the ground in late November or early December. The wingless adult females climb up the trunk of the host tree and lay barrel-shaped eggs in masses on twigs and branches. The eggs hatch and larvae begin feeding about the same time leaves begin to emerge. The larvae drop down and dangle on silken threads until swept away by a breeze. The ballooning larvae may travel from plant to plant until a suitable host plant is found. The larvae feed for about a month before they fall to the ground to pupate. The worms have brown backs with white stripes running lengthwise down their backs. The fall cankerworm has three sets of prolegs with the foremost proleg severely stunted. This distinguishes it from the spring cankerworm that has only two pairs of prolegs.
SPRING CANKERWORM: The adult spring cankerworm, Paleacrita vernata, emerges in late February or early March. The wingless adult females climb up the trunk of the tree and lay barrel-shaped eggs in cracks in the bark and underneath the bark and bud scales. Yellow-striped green worms hatch at the same time as fall cankerworm larvae and follow the same general feeding pattern. They too drop to the ground where the larvae overwinter in a protective cell. Spring cankerworm larvae have only two pairs of prolegs.
Integrated Pest Management Strategies
1. Sticky barriers may be banded around tree trunks. Apply a band of a sticky material, such as Tanglefoot, around the trunks of trees in October. The sticky material will trap the wingless females of the fall cankerworm moths as they crawl up the tree trunk to lay eggs in late November or early December. Renew the traps in February to trap the emerging female adults of the spring cankerworm that climb the trunk to lay eggs in late February or early March.
2. Prevent larvae from emerging. In the spring apply a horticultural oil spray on the tree before the larvae hatch, about the time trees just begin to leaf out in the spring.
3. Spray Bt (Bacillus thuringiensis) or Sevin after leaves are fully expanded and flowering is finished. Repeat this application two more times, at 14-day intervals. Sevin is very toxic to bees, hence spraying should be delayed until after flowering to limit damage to these beneficial insects.
Symptoms and Diagnosis
Leaves are chewed. Complete defoliation and crop loss may occur; or after repeated damage, less and less fruit is produced until little, if any, fruit matures. Damage is first evident in the early spring or summer after trees have fully leafed out. This is about the time that larvae of both species emerge and begin to feed.
Life Cycle
Cankerworms are small caterpillars, only getting up to an inch long. Adult males are small, gray moths with a wingspan reaching only 1 inch long. The females of both species are wingless.
FALL CANKERWORM: The adult fall cankerworm, Alsophila pometaria, emerges from the ground in late November or early December. The wingless adult females climb up the trunk of the host tree and lay barrel-shaped eggs in masses on twigs and branches. The eggs hatch and larvae begin feeding about the same time leaves begin to emerge. The larvae drop down and dangle on silken threads until swept away by a breeze. The ballooning larvae may travel from plant to plant until a suitable host plant is found. The larvae feed for about a month before they fall to the ground to pupate. The worms have brown backs with white stripes running lengthwise down their backs. The fall cankerworm has three sets of prolegs with the foremost proleg severely stunted. This distinguishes it from the spring cankerworm that has only two pairs of prolegs.
SPRING CANKERWORM: The adult spring cankerworm, Paleacrita vernata, emerges in late February or early March. The wingless adult females climb up the trunk of the tree and lay barrel-shaped eggs in cracks in the bark and underneath the bark and bud scales. Yellow-striped green worms hatch at the same time as fall cankerworm larvae and follow the same general feeding pattern. They too drop to the ground where the larvae overwinter in a protective cell. Spring cankerworm larvae have only two pairs of prolegs.
Integrated Pest Management Strategies
1. Sticky barriers may be banded around tree trunks. Apply a band of a sticky material, such as Tanglefoot, around the trunks of trees in October. The sticky material will trap the wingless females of the fall cankerworm moths as they crawl up the tree trunk to lay eggs in late November or early December. Renew the traps in February to trap the emerging female adults of the spring cankerworm that climb the trunk to lay eggs in late February or early March.
2. Prevent larvae from emerging. In the spring apply a horticultural oil spray on the tree before the larvae hatch, about the time trees just begin to leaf out in the spring.
3. Spray Bt (Bacillus thuringiensis) or Sevin after leaves are fully expanded and flowering is finished. Repeat this application two more times, at 14-day intervals. Sevin is very toxic to bees, hence spraying should be delayed until after flowering to limit damage to these beneficial insects.
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