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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Blossom-end rot is a physiological disorder of tomatoes and peppers. It is a disturbance in the normal physiology of the plant. Because it is not caused by an insect or disease organism, fungicidal and insecticidal sprays are not effective in controlling the problem.
Symptoms and Diagnosis An early symptom of blossom-end rot is a light tan patch on the blossom end of the green fruit. Over time the area turns dark brown or black and may become sunken or leathery. Fruit which is one-third to one-half developed is most commonly affected. Sometimes an internal black rot will develop in the center of the fruit with little or no external symptoms. Parts of the fruit not affected by blossom-end rot may be eaten.
Causes of Blossom-End Rot The most common cause of blossom-end rot is fluctuating soil moisture. Moisture plays an important role in calcium uptake in the plant. When a dry period follows adequate moisture, calcium uptake can be reduced. Root damage due to deep cultivation or burning from improper fertilization can also restrict calcium uptake. Excessive applications of fertilizer containing ammonia can also result in symptoms. Less frequently, an actual deficiency of calcium in the soil may cause this rot. This is rarely the case in St. Louis.
Integrated Pest Management Strategies 1. Maintain even soil moisture. Water regularly during dry periods and mulch plants with a 3–4 inch layer of organic material to help hold in soil moisture. 2. Avoid deep cultivation too near plants. 3. Modify your fertilizing practices. Use a fertilizer high in superphosphate and low in nitrogen. When adding nitrogen, use calcium nitrate rather than ammonia or urea forms.
4. Get a soil test. If the above methods do not correct the problem, get a soil test and maintain soil pH at 6.5 to 7. 5. As a last resort, use a foliar spray of calcium chloride. Do not spray too often or in excessive amounts. 6. Tomatoes in container. For tomatoes grown in containers, apply a fertilizer specifically formulated for tomatoes. The fertilizer must contain micronutrients including calcium.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Blossom-end rot, which begins with a small watery bruise on the blossom end of the fruit, is the result of a lack of calcium in developing fruits. This calcium deficiency can be a result of slow growth, damaged roots induced by extreme fluctuations in the surrounding soil moisture content, an excess of salts, or other fluctuating conditions during plant growth. Calcium deficiencies cause actively growing cells to die because they cannot retain water and nutrients.
Symptoms and Diagnosis Blossom-end rot begins as a water-soaked, sunken spot on the blossom end (the end that isn't attached to the stem) of the fruit. The spot may enlarge and become depressed as the fruit grows. The spot may turn from brown to black and become moldy. Blossom-end rot can be distinguished from other rots by its confinement to the blossom end. It may also be confused with rotting fruit that results from the failure of female flowers to set fruit due to lack of male flowers or pollinating insects.
Integrated Pest Management Strategies 1. Plant cucurbits in a location that has well-drained soil. 2. Mulch the plants and water properly to maintain a uniform moisture level in the soil. Avoid damaging the root system when hoeing or weeding. 3. Test the garden soil pH. Calcium may not be available to plants if the soil pH is too low or high.
4. Limit the use of high ammonia fertilizers and fresh manure that may stimulate lush growth and add more salts to the soil. 5. Add calcium nitrate to soil or spray with 1% calcium chloride in order to boost the amount of calcium available to developing fruit. 6. Cucurbits in containers. For cucurbits grown in containers, apply a fertilizer that contains micronutrients including calcium. Many fertilizers formulated for tomatoes meet these specifications.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Cucumber bacterial wilt is caused by the bacterium, Erwinia tracheiphila, and is characterized initially by wilting and drying of individual leaves, especially those exhibiting cucumber beetle injury. Cucumbers and muskmelons are more susceptible than pumpkins or squash; the disease is rarely a problem on watermelons.
Symptoms and Diagnosis Infected plants initially show wilting and drying of individual leaves. As the leaves wilt and shrivel, stems may dry out suddenly. Later, wilting spreads to entire branches and vines. Wilting will occur during the middle of the day during periods with high water stress. The vine may recover at night. Eventually, however, the entire vine will wither, collapse, and die. In partially resistant plants, symptoms appear as dwarfing, excessive blooms, and branching. A good diagnostic test for this wilt is to cut a wilted stem near the base. Touch a knife blade to the cut and draw away from the cut. White to clear strings of the bacterial ooze will be strung out from the cut made on the infected plant to the knife blade. This diagnostic test is not 100% reliable. Further investigation may be necessary.
Life Cycle The bacteria overwinter in the digestive system of the cucumber beetle. In the spring, bacterial wilt is spread from plant to plant through both the striped and spotted cucumber beetles that feed on cucumbers and other relatives of this family. The bacteria are released through the insect excrement and move into host plants through the stomates and wounds, most likely the ones made when the insects feed. Insects ingest more bacteria as they feed on infected plants, and the cycle is repeated.
Integrated Pest Management Strategies 1. Protect plants with netting. Prevent cucumber beetles from feeding and infecting plants by covering them with netting or porous fabric. 2. Remove and destroy plant material when symptoms of wilting are first noticed. There are no cures for the disease. Beetles spread the bacterium from infected plants to healthy plants. 3. Grow susceptible crops on rotation every third year. Since beetles overwinter in the soil and carry the bacterium, the cycle can be disrupted by only planting the host in an area every third year.
4. Avoid planting cucurbits next to corn. Spotted cucumber larvae also feed on corn; avoiding close plantings of these two crops may help control the beetles on cucurbits. 5. Grow varieties that tolerate bacterial wilt like butternut or acorn squash and Saladin or County Fair 83 cucumbers. No muskmelon varieties are known to be tolerant to bacterial wilt. 6. Dust plants with insecticide in the spring before the cucumber beetles have a chance to lay eggs (April-June). Apply pyrethrin or carbaryl (Sevin). Try an insecticide-bait combination such as Adios that has cucurbitacin, the beetle attractant, and a small amount of carbaryl (Sevin).
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Sycamore anthracnose is a fungal disease that can cause leaf drop, twig dieback, cankers and the sudden death of more than 90% of a tree’s new shoot growth. Although the disease is rarely fatal and trees will grow a second set of leaves, repeat infections will result in abnormal branching and will leave a tree stressed and more susceptible to other diseases and pests. American sycamore or buttonwood (Platanus occidentalis), London plane tree (P. x acerifolia) and Oriental plane tree (P. orientalis) may all be affected by sycamore anthracnose.
Symptoms and Diagnosis Sycamore anthracnose is most common during the cool wet weather of spring and is often mistaken for frost damage. As new leaves unfold, they crinkle and turn brown, wilt rapidly and fall. Dark and sunken dead areas form along the veins of older leaves eventually expanding to include the entire leaf. The tree may also develop cankers on twigs and older branches resulting in twig dieback and the girdling and death of the larger branches. Small black dots, the fruiting bodies of the fungus, may be visible. The clusters of dead twigs will result in abnormal branching such as witches’ brooms or as the twigs die, break and fall, the tree will appear ragged. Reportedly, London plane tree is less susceptible to cankers than the American sycamore.
Life Cycle The sycamore anthracnose fungus, Apiognomonia veneta, overwinters in diseased leaves and in cankers on twigs and branches. Spores are produced in spring and spread by rain. If the mean daily temperatures are 50 – 55 degrees F., the spores will germinate and the resulting infections will cause the death of new buds, shoots and leaves. The disease will be slight or will not occur by late spring or midsummer when the mean daily temperatures are 60 degrees F. or greater and the tree will be able to produce a second set of leaves. The fungus may also infect twigs and buds in fall after leaf drop.
Integrated Pest Management Strategies 1. Be patient. The tree may appear to be dead but will probably recover and develop new leaves and shoots. 2. Practice good garden sanitation by raking up and disposing of fallen leaves and twigs. 3. Practice good cultural techniques to keep plants healthy and free of drought, nutritional or injury-induced stress. Water trees twice a month during dry winters. 4. Prune out dead branches when possible. Disinfect pruning shears in a 10% bleach solution between cuts to avoid spreading the disease. 5. Prune branches to improve air circulation reducing the length of time leaves are wet and thus susceptible to infection.
6. Treat with a preventive systemic fungicide. This treatment may require the services of a certified arborist. 7. Spray with a preventive fungicide such as lime-sulfur (Bordeaux mixture) or chlorothalonil (daconil) when leaves begin to emerge from buds. Reapply two or three more times at 7-10 day intervals. Fungicides are not effective after the leaves have been infected. Large trees may require the services of a certified arborist. 8. Plant resistant species or cultivars. Oriental plane tree (zones 7-9) and London plane tree cultivars, ‘Bloodgood’, ‘Columbia’ and ‘Liberty’ are less susceptible to the disease than the American sycamore.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Rose rosette disease, also known as witches’-broom of rose, is caused by a virus (Emaravirus sp.) that is spread by a very small, eriophyid mite. The disease is limited to plants in the genus Rosa but R. setigera, R. aricularis, R. arkansana, R. blanda, R. palustris, R. carolina and R. spinosissima are believed to be resistant. Its main host is the multiflora rose, which is considered a noxious weed throughout much of the United States. Interest in rose rosette has been generated by the threat to garden roses and its possible use as a biocontrol for multiflora rose.
Symptoms and Diagnosis The earliest symptoms of rose rosette disease include a red pigmentation of the underside of leaf veins followed by sharply increased growth of vegetative shoots, which are typically more succulent than normal and colored in various shades of red. Leaves often become deformed, crinkled, and brittle with yellow mosaics and red pigmentation. As the disease progresses, leaves become very small, petioles are shortened, and most lateral buds grow, producing short, intensely red shoots. The disease causes the plant to be exceptionally susceptible to freeze damage. Symptoms on cultivated roses are typically less severe than on multiflora rose. Cultivated roses show symptoms of thickened, succulent stems and a proliferation of thorns. Symptoms can mimic some forms of herbicide damage.
Life Cycle The disease is transmitted by an eriophyid mite, a wingless mite that can travel passively in the wind as well as on contaminated clothing and equipment. The mites are most prevalent in the apex of the rose shoots where they feed and reproduce. Females overwinter under bark or on bud scales of living roses. The females move to newly developing shoots where they lay one egg a day for about 30 days. The young hatch in 3-4 days. They can reach adulthood in about a week depending upon temperatures. Multiple generations occur each year until fall when females seek overwintering sites. The mites are hampered by low humidity and can only survive about 8 hours without being on a host plant. Virus transmission occurs most readily between the months of May through mid-July when plants are making active growth. Symptoms from new infections usually start appearing in mid-July. In general, smaller plants go through the disease stages more quickly than larger plants. Small plants are usually killed in about 2 years, while a large plant may survive for five years in a deteriorated condition.
Integrated Pest Management Strategies 1. Remove ornamental roses with symptoms. The entire plant including the roots should be removed and destroyed by burning or placing in a plastic bag. Care must be taken when working with diseased plants as you can facilitate spread of the mites that spreads the disease. Bag the plant before removal, cut it at ground level and then dig out the plant’s roots. Soil need not be removed. Clean tools and put on fresh clothing before moving to a disease-free plant or area. 2. Plant ornamental roses as far away as possible from known stands of multiflora rose. The general recommendation is maintain at least 300 feet between your roses and any stands of multiflora rose. Even greater distance is preferred especially if they are upwind of your desirable rose plants.
3. Control the disease by controlling the mite. Start mite control early by pruning your roses hard in late winter (back by 2/3) to remove as many overwintering mites as possible and then spray with horticultural oil to kill any remaining mites. Organic pesticides such as horticultural oils and insecticidal soap are recommended over other pesticides as these organic pesticides are less harmful to natural predators that feed on the problem mites. Apply weekly during the months of June and July paying particular attention to the new growing tips where the mites will congregate. Refrain from using leaf blowers around roses as they can spread mites.
4. Help to isolate your roses. Do not plant roses too close together. With extra space between the plants mite movement can be reduced. Also, consider interplanting roses with other ornamental plants. 5. Using rose rosette disease as an IPM strategy. The multiflora rose is an exotic invasive species that is responsible for the degradation of millions of acres of farmland and recreational areas. Using the disease to control this invasive weed can cut costs and be considered environmentally friendly for reducing the amount of synthetic chemicals used. However, the disease also affects cultivated roses. One should be extremely cautious and good neighbor-minded when it comes to rose rosette disease.
6. Plant a resistant cultivar. Rose breeders have been working to develop new rose cultivars that are resistant to rose rosette. The first, 'Top Gun', is a shrub rose that is scheduled to be released in 2018. 'Top Gun' is also reportedly resistant to most other common rose diseases. Others cultivars are planned to follow.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Oak leaf blister (oak leaf curl) is a fungal leaf disease caused by the fungus Taphrina caerulescens. Circular, raised areas ranging up to 2 inches in diameter are scattered over the upper leaf surface. During cool wet springs, almost all species of oak are subject to the leaf blister disease. Members of the red oak family are particularly susceptible to infection. The disease is closely related to Taprina deformans which causes peach leaf curl.
Symptoms and Diagnosis Blister-like, circular, raised areas appear scattered on the upper leaf surface. This raised area causes a corresponding depression on the lower leaf surface at the same site and of the same size. The color of the upper convex area is yellowish white while the bottom concave area is yellowish brown. Leaves with numerous spots may fall prematurely to the ground. If well-established trees defoliate before midsummer, they will sometimes leaf out later in the season. When defoliation occurs in late summer, leaf loss will have little impact on the overall health of the tree.
Life Cycle During mid-spring, microscopic spores are produced in leaf spots. These spores are carried by wind and splashing raindrops onto bud scales and twigs where they remain in a dormant stage until the following early spring. At this time, rain washes the spores onto young leaves where infection takes place. Depending on weather conditions, small circular spots begin to develop in 2 to 4 weeks. Spores produced on these spots will lodge in bud scales and again remain resting until the following spring. Cool wet weather is required for germination on young leaves, and if these conditions continue, severe infection can occur. If weather conditions are not favorable for spore germination shortly after bud break, only minor infection will occur. As the leaves mature, they become more resistant to infection.
Integrated Pest Management Strategies 1. Maintain plant vigor. Keep the tree well watered during drought conditions (approximately 1 inch of water per week) and well-drained during periods of heavy rain. Fertilize according to soil test recommendations. Apply nitrogen every 3 to 5 years for mature shade trees. 2. General health. Oak leaf blister does not seriously affect the overall health of the tree unless the tree is repeatedly defoliated in successive years. Even if this occurs, the second set of leaves should emerge at a time when conditions are not conducive to reinfection of leaves and newly formed bud scales.
3. Fungicides. A single application of a fungicide applied in the spring at the time of bud-swelling is usually adequate. Apply with a power sprayer and coat buds and twigs thoroughly for good control. chlorothalonil (Daconil) is currently registered for use in controlling oak leaf blister. Fungicides will not be effective if applied after bud break. As with the use of all chemicals, carefully read and follow the manufacturer’s directions.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Cornus species are riddled with leaf diseases. After the discovery of dogwood anthracnose that devastated the dogwood population in the northeastern U.S., it has been increasingly more significant to be on alert for disease outbreaks. Three leaf spot diseases that show themselves in varying degrees are dogwood anthracnose, spot anthracnose, and powdery mildew. Dogwood anthracnose and powdery mildew are of particular concern. Dogwood anthracnose was confirmed in St. Louis in 2012 and again in 2015. Powdery mildew can occur yearly.
Symptoms and Diagnosis Symptoms of Dogwood Anthracnose: Dogwood anthracnose is a disease caused by the fungus, Discula destructiva. Since its discovery in the 1970s, the spread has been swift and the results disastrous to the native Cornus florida. Symptoms include leaf spots that are soft and very wet with purple borders, twig blight, dead leaves that cling to the tree, epicormic shoots (water sprouts with many shoots occurring near the base of the tree), lower branch dieback, and eventually death. Conditions that favor disease include low light levels, high humidity, and temperatures of 60 F. In the St. Louis area it was found in the Kirkwood/Ladue area in 2012 and the Brentwood area in 2015. It is considered established in St. Louis.
Symptoms of Spot Anthracnose: Spot anthracnose is caused by the fungus, Elsinoe corni. Symptoms include small, dark, pinprick lesions with purple borders on leaf surfaces. The lesions are numerous and usually occur on dry leaves. The disease is unsightly, but typically not very harmful. Symptoms of Powdery Mildew: Powdery mildew is caused by the fungus, Microsphaera pulchra. Early symptoms include round, white or gray powder-like spots that appear on upper leaf surfaces. These spots form a dry white layer on leaves. As young leaves become infected, they appear twisted, dry, and leathery. Older leaves look bronzed. Moderate temperatures, low light, and high humidity accelerate this disease. High nitrogen levels cause the disease to flourish.
Integrated Pest Management Strategies 1. Choose disease resistant varieties. A soon-to-be released cultivar for dogwood anthracnose resistance is called ‘Appalachian Spring’. Cultivars less susceptible to spot anthracnose include ‘Cherokee Princess’, ‘Cherokee Sunset’, and ‘Springtime’. ‘Cherokee Brave’, C. kousa, and C. kousa x C. florida crosses are resistant to powdery mildew. 2. Water the roots of the tree. Avoid using overhead irrigation in order to reduce the incidence of leaf spot.
3. Practice good sanitation. Promptly remove and dispose of any dead or dying twigs or branches found in trees as well as leaves that show the symptoms of dogwood anthracnose. Leaves with spot anthrancnose and powdery mildew can remain but rake and remove them in the fall when they drop. 4. Remove plants confirmed with dogwood anthracnose. Removing an infected tree confirmed with dogwood anthracnose is strongly recommended. The infected trees should NOT be converted to mulch to avoid spreading the disease.
5. Apply fungicides. If you suspect dogwood anthracnose, get it diagnosed by a professional prior to a fungicide application. Powdery mildew should also be controlled, especially if the disease has occurred previously.
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来自： Bailu_Yuan
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武汉
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南昌
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