文章
Dummer. ゛☀
2017年09月23日
Ever have one of those days when you feel a little sluggish and bloated? Well, your plants can have the same problem — they retain water just like people do when conditions are not right. Edema in plants is not a serious disease and it’s not a symptom of a bacteria, virus or insect infestation. Common causes of plant edema include over watering and improper fertilization; it’s easily curable if caught early.
What is Edema?
Edema, or oedema, is a type of abnormal water retention in plants, often influenced by the plant’s environment. Favorable conditions actually encourage edema in many cases, since affected plants already have a fair amount of water in their systems, providing them with more can just encourage them to gorge on liquid. Any time the plant takes up water faster than it transpires, edema becomes a risk. Signs of edema plant disease vary between susceptible species, but often include bumps, blisters or water-soaked areas on the undersides of leaves. These areas may expand and become corky, but in other plants, curling and distortion are common. White, crusty eruptions may form along the leaf veins or gall-like structures can develop under leaves with yellow corresponding spots on the upper leaf surface.
Treating Edema
Because it’s not a disease, there are many ways to treat edema, depending on the cause. Your job as gardener is to figure out what’s causing your plant’s problem and correct the situation. If your plant has edema, first adjust your watering habits. Most plants should never sit in water, so remove those saucers and make sure that big pots are draining well. Roots tend to absorb water faster when the water is warm and the atmosphere is cool, so wait to water until the sun is up in the morning whenever possible. Indoors, humidity can have a considerable influence on edema; improving air circulation around plants will help reduce humidity into safer ranges.
Increasing the light intensity is helpful for many plants with edema, but be sure not to cook them by moving them too quickly into brighter light. Make these changes gradually, over the course of a week or two, slowly leaving the plant in brighter light for an increasing length of time, until it no longer wilts in response to the sun. Lastly, make sure you’re fertilizing your plant properly. Plants with low available potassium and calcium can be more susceptible to edema. If cultural conditions seem correct for your plant, a soil test may be needed. Adjusting the pH can make more nutrients available, or you may need to add more of the nutrients that are lacking.
What is Edema?
Edema, or oedema, is a type of abnormal water retention in plants, often influenced by the plant’s environment. Favorable conditions actually encourage edema in many cases, since affected plants already have a fair amount of water in their systems, providing them with more can just encourage them to gorge on liquid. Any time the plant takes up water faster than it transpires, edema becomes a risk. Signs of edema plant disease vary between susceptible species, but often include bumps, blisters or water-soaked areas on the undersides of leaves. These areas may expand and become corky, but in other plants, curling and distortion are common. White, crusty eruptions may form along the leaf veins or gall-like structures can develop under leaves with yellow corresponding spots on the upper leaf surface.
Treating Edema
Because it’s not a disease, there are many ways to treat edema, depending on the cause. Your job as gardener is to figure out what’s causing your plant’s problem and correct the situation. If your plant has edema, first adjust your watering habits. Most plants should never sit in water, so remove those saucers and make sure that big pots are draining well. Roots tend to absorb water faster when the water is warm and the atmosphere is cool, so wait to water until the sun is up in the morning whenever possible. Indoors, humidity can have a considerable influence on edema; improving air circulation around plants will help reduce humidity into safer ranges.
Increasing the light intensity is helpful for many plants with edema, but be sure not to cook them by moving them too quickly into brighter light. Make these changes gradually, over the course of a week or two, slowly leaving the plant in brighter light for an increasing length of time, until it no longer wilts in response to the sun. Lastly, make sure you’re fertilizing your plant properly. Plants with low available potassium and calcium can be more susceptible to edema. If cultural conditions seem correct for your plant, a soil test may be needed. Adjusting the pH can make more nutrients available, or you may need to add more of the nutrients that are lacking.
0
0
文章
Dummer. ゛☀
2017年09月19日
Early blight is a fungal disease, Alternaria sp., that occurs on tomatoes throughout North America. Early blight can affect seedlings but is generally observed on older plants and is especially severe on plants of poor vigor. Plants infected with the fungus can display collar rust on the stems, infected older leaves, and fruits that crack at the stem. Infection on leaves is the most common symptom.
Symptoms and Diagnosis
The appearance of circular or irregular dark spots on the lower, more mature leaves is one of the first symptoms of infection. Eventually, the spots enlarge into a series of concentric rings surrounded by a yellow area. The entire leaf may be killed and will drop off the plant. Early blight can result in extensive defoliation, exposing fruit to sunscald and reducing yields. This disease typically progresses from the base of the plant, upward.
Life Cycle
Early blight spores survive on old plant debris or in the soil. Spores are spread by wind and rain, but occasionally, flea beetles transmit this disease. Fungal spores enter a host through wounds in the plant cuticle. Spores thrive in moist, warm temperatures (80–90 degrees F) and can persist in partially decomposed garden waste for at least a year.
Integrated Pest Management Strategies
1. Plant resistant varieties. Varieties such as ‘Early Cascade’, ‘Floramerica’, ‘Jetstar’, ‘Manlucie’, ‘Supersonic’, and ‘Surecrop’ have some tolerance to early blight. These varieties will require a less intensive management program than susceptible varieties.
2. Maintain plant vigor. Stressed plants are more susceptible to early blight. Water the plants regularly, but don't fertilize until the plants are well-established and in full blossom. Do not mulch until the soil is warm.
3. Do a thorough cleanup of the garden in the fall. Remove plant debris or till it into the soil. Pull weeds that compete for light, water, and nutrients, especially nightshade, horse nettle, and other weeds in the tomato family.
4. Rotate crops. Practice a 2- or 3-year crop rotation. Avoid planting eggplant or potatoes where tomatoes were last planted.
5. Avoid activity when plants are wet. Confine staking and picking to times when foliage is dry. Disease is more readily spread when plant foliage is wet.
6. Protect clean foliage with a fungicide. Effective fungicides include copper (Kocide), chlorothalonil (Bravo, Daconil), mancozeb, or maneb. Apply at fruit set and reapply every 7–14 days.
Symptoms and Diagnosis
The appearance of circular or irregular dark spots on the lower, more mature leaves is one of the first symptoms of infection. Eventually, the spots enlarge into a series of concentric rings surrounded by a yellow area. The entire leaf may be killed and will drop off the plant. Early blight can result in extensive defoliation, exposing fruit to sunscald and reducing yields. This disease typically progresses from the base of the plant, upward.
Life Cycle
Early blight spores survive on old plant debris or in the soil. Spores are spread by wind and rain, but occasionally, flea beetles transmit this disease. Fungal spores enter a host through wounds in the plant cuticle. Spores thrive in moist, warm temperatures (80–90 degrees F) and can persist in partially decomposed garden waste for at least a year.
Integrated Pest Management Strategies
1. Plant resistant varieties. Varieties such as ‘Early Cascade’, ‘Floramerica’, ‘Jetstar’, ‘Manlucie’, ‘Supersonic’, and ‘Surecrop’ have some tolerance to early blight. These varieties will require a less intensive management program than susceptible varieties.
2. Maintain plant vigor. Stressed plants are more susceptible to early blight. Water the plants regularly, but don't fertilize until the plants are well-established and in full blossom. Do not mulch until the soil is warm.
3. Do a thorough cleanup of the garden in the fall. Remove plant debris or till it into the soil. Pull weeds that compete for light, water, and nutrients, especially nightshade, horse nettle, and other weeds in the tomato family.
4. Rotate crops. Practice a 2- or 3-year crop rotation. Avoid planting eggplant or potatoes where tomatoes were last planted.
5. Avoid activity when plants are wet. Confine staking and picking to times when foliage is dry. Disease is more readily spread when plant foliage is wet.
6. Protect clean foliage with a fungicide. Effective fungicides include copper (Kocide), chlorothalonil (Bravo, Daconil), mancozeb, or maneb. Apply at fruit set and reapply every 7–14 days.
0
0
文章
Dummer. ゛☀
2017年09月19日
Clubroot is a fungal disease that affects a number of plants in the cabbage family including cabbages, radish, mustard and ornamentals such as candytuft. It is caused by the fungus Plasmodiophora brassicae and gets its name from the club-like roots it induces in infected plants. Its diagnosis is often missed as the infected plant part, the roots, are underground and out of sight.
Symptoms and Diagnosis
The first symptom is usually wilting during average daily conditions but recovery at night. The older leaves may yellow and die and the plants look stunted. Examination of the root system reveals enlarged roots that make them look club-like and reduced feeder roots. The reduction in feeder roots as well as disruption of the water conducting tissue in the roots causes the drought-like symptoms. Development of the disease if favored by a low soil pH (below 7.0), cool soil, and excess soil moisture. The organism can survive in the soil for over 10 years. Since most soils in the St. Louis area are above a pH of 7 the disease is rare in our area.
Life Cycle
Clubroot is a soil-borne fungus that infects plants through root hairs by zoospores. After infection the roots enlarge and many spores are produced in the swollen roots. The mobile zoospores can re-infect other roots on the plant or nearby plants. Late in the season resting spores are produced. When roots die and decay the resting spores are released into the soil where they can survive for many years and be transported through the soil by water movement and garden equipment.
Integrated Pest Management Strategies
1. Remove diseased plants. The disease organism can reside in the soil for many years so although quick removal of diseased plants is recommended the disease may return if plants in the cabbage family are planted in the infested soil the following year. Also remove any cabbage family weeds such as wild mustard, which can harbor the disease.
2. Add lime. Since problems are more severe in acid soils (pH 5.0-7.0) adding lime to acid soils can help control the disease.
3. Rotate crops Rotate where you grow cabbage, radishes, mustards, etc in your garden. Wait 5-6 years before replanting in an area.
Symptoms and Diagnosis
The first symptom is usually wilting during average daily conditions but recovery at night. The older leaves may yellow and die and the plants look stunted. Examination of the root system reveals enlarged roots that make them look club-like and reduced feeder roots. The reduction in feeder roots as well as disruption of the water conducting tissue in the roots causes the drought-like symptoms. Development of the disease if favored by a low soil pH (below 7.0), cool soil, and excess soil moisture. The organism can survive in the soil for over 10 years. Since most soils in the St. Louis area are above a pH of 7 the disease is rare in our area.
Life Cycle
Clubroot is a soil-borne fungus that infects plants through root hairs by zoospores. After infection the roots enlarge and many spores are produced in the swollen roots. The mobile zoospores can re-infect other roots on the plant or nearby plants. Late in the season resting spores are produced. When roots die and decay the resting spores are released into the soil where they can survive for many years and be transported through the soil by water movement and garden equipment.
Integrated Pest Management Strategies
1. Remove diseased plants. The disease organism can reside in the soil for many years so although quick removal of diseased plants is recommended the disease may return if plants in the cabbage family are planted in the infested soil the following year. Also remove any cabbage family weeds such as wild mustard, which can harbor the disease.
2. Add lime. Since problems are more severe in acid soils (pH 5.0-7.0) adding lime to acid soils can help control the disease.
3. Rotate crops Rotate where you grow cabbage, radishes, mustards, etc in your garden. Wait 5-6 years before replanting in an area.
0
0
文章
Dummer. ゛☀
2017年09月19日
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.
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.
0
0
文章
Dummer. ゛☀
2017年09月19日
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.
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.
0
0
文章
Dummer. ゛☀
2017年09月19日
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.
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.
0
0
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.
0
0
文章
Dummer. ゛☀
2017年09月19日
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.
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.
0
0
文章
Dummer. ゛☀
2017年09月19日
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.
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.
0
0
文章
Dummer. ゛☀
2017年09月19日
Guignardia blotch is a foliage disease of many Aesculus species, including California, Ohio, red, and yellow buckeye and common, red, and Japanese horse chestnuts. Bottlebrush buckeye (A. parviflora) and some varieties of Ohio buckeye (A. glabra varieties arguta, monticola, and sargentii) may be resistant.
The leaves of affected plants develop large reddish brown blotches surrounded by yellow tissue, often causing the foliage to curl and brown. In severe cases, leaves may fall prematurely in late summer. Since the foliage is usually not badly damaged until after the tree has completed much of its annual growth, the disease is primarily aesthetic.
Wet weather promotes the growth of Guignardia blotch. In the United States, this fungal disease only occurs east of the Great Plains, perhaps because of the drier conditions of the West. This disease may become severe in nurseries or in plantings where tree crowns are close together.
Symptoms and Diagnosis
Guignardia blotch first appears as water-soaked irregular areas. These enlarge quickly and in a few days are reddish-brown to brown leaf spots with clear bright yellow margins. The blotches vary in size and may frequently grow together, covering large areas of leaf tissue. This causes the leaf to curl and brown, becoming dry and brittle, and may cause early leaf drop. Fruiting bodies of the fungus, seen as black pinhead-sized specks, may be visible in the lesions. Occasionally petioles and immature fruit may also have small reddish brown lesions. Symptoms of this disease are similar to those of environmental leaf scorch. Leaves affected by scorch will be on the sunny or windy side of the tree while Guignardia blotch may affect most leaves. Scorched leaves will not have the black fruiting bodies. See also “Scorch of Trees and Shrubs”.
Life Cycle
The Guignardia fungus overwinters on fallen Aesculus leaves. In early spring, its fruiting bodies mature and during wet weather, they release spores into the air. If the spores land on newly developing susceptible leaves that remain wet for several hours, the leaves become infected, resulting in blotches within 10–20 days. New fruiting bodies develop in early June and in wet weather, more infections may continue throughout the summer.
Integrated Pest Management Strategies
1. Sanitation. Rake and dispose of infected leaves.
2. Pruning. Thin the tree canopy to improve air circulation and to speed drying of leaves.
3. Fungicides. Chemical treatment is usually not necessary or recommended in the home landscape. Serious damage may be controlled by applying a fungicide containing chlorothalonil or mancozeb at bud break and then repeating the application at 10 to 14 day intervals as long as wet conditions continue.
The leaves of affected plants develop large reddish brown blotches surrounded by yellow tissue, often causing the foliage to curl and brown. In severe cases, leaves may fall prematurely in late summer. Since the foliage is usually not badly damaged until after the tree has completed much of its annual growth, the disease is primarily aesthetic.
Wet weather promotes the growth of Guignardia blotch. In the United States, this fungal disease only occurs east of the Great Plains, perhaps because of the drier conditions of the West. This disease may become severe in nurseries or in plantings where tree crowns are close together.
Symptoms and Diagnosis
Guignardia blotch first appears as water-soaked irregular areas. These enlarge quickly and in a few days are reddish-brown to brown leaf spots with clear bright yellow margins. The blotches vary in size and may frequently grow together, covering large areas of leaf tissue. This causes the leaf to curl and brown, becoming dry and brittle, and may cause early leaf drop. Fruiting bodies of the fungus, seen as black pinhead-sized specks, may be visible in the lesions. Occasionally petioles and immature fruit may also have small reddish brown lesions. Symptoms of this disease are similar to those of environmental leaf scorch. Leaves affected by scorch will be on the sunny or windy side of the tree while Guignardia blotch may affect most leaves. Scorched leaves will not have the black fruiting bodies. See also “Scorch of Trees and Shrubs”.
Life Cycle
The Guignardia fungus overwinters on fallen Aesculus leaves. In early spring, its fruiting bodies mature and during wet weather, they release spores into the air. If the spores land on newly developing susceptible leaves that remain wet for several hours, the leaves become infected, resulting in blotches within 10–20 days. New fruiting bodies develop in early June and in wet weather, more infections may continue throughout the summer.
Integrated Pest Management Strategies
1. Sanitation. Rake and dispose of infected leaves.
2. Pruning. Thin the tree canopy to improve air circulation and to speed drying of leaves.
3. Fungicides. Chemical treatment is usually not necessary or recommended in the home landscape. Serious damage may be controlled by applying a fungicide containing chlorothalonil or mancozeb at bud break and then repeating the application at 10 to 14 day intervals as long as wet conditions continue.
0
0
文章
Dummer. ゛☀
2017年09月19日
Dutch elm disease is a wilt disease caused by the fungus, Ceratocystis ulmi. It was described in Ohio in 1930. By the 1980's, it could be found in most of the U.S. It is a serious and fatal disease of American elms. Even after years of study, there is no effective cure for the disease.
Symptoms and Diagnosis
Symptoms develop rapidly during a period of 4–6 weeks after leaves reach full size. The first visible symptoms are yellowing of foliage followed by wilting and browning, a condition called flagging. Usually a single branch is affected first; wilted branches die rapidly and leaves brown, curl, and often drop prematurely. The symptoms spread to nearby branches and then to one whole part of the tree. The entire tree finally wilts and dies. This progression of symptoms may develop in one season or may take several years. Positive diagnosis of the disease requires a laboratory test to culture the fungal pathogen.
Life Cycle
The fungus is primarily dependent on insectvectored transmission from tree to tree over long distances. There are 2 vectors for the fungus in North America, the native American elm bark beetle and the less prevalent European elm bark beetle. Both of these beetles feed and breed under the bark of living or recently dead elm trees or logs. They carry the spores of the fungus from infected trees and innoculate healthy trees as they feed. Both species of elm bark beetles are effective carriers. The cycle of infection by the fungus is tied to the life cycle of the vectors. The beetles breed in recently dead elm wood or weakened living trees. If the fungus is present in breeding sites, emerging beetles will carry spores to healthy elms and introduce the fungus in feeding sites on young twigs. The beetles can fly up to 1/4 mile in search of feeding or breeding sites, but they may be blown many miles by winds. The disease may also spread by root grafts from a diseased elm tree to a healthy elm tree provided that the root systems overlap.
Integrated Pest Management Strategies
1. There is no cure for the disease. If your elm tree has leaves yellowing or wilting on one or more branches, cut off several small branches and look for brown streaking in the sapwood. If brown streaking is evident, a laboratory test is suggested for positive identification. This disease may be confused with other canker and wilt pathogens of elm.
2. Maintain plant health. Provide adequate amounts of water and fertilizer. Mild cases of Dutch elm disease may respond to pruning of diseased wood if less than 5% of the tree is infected. Control the insect vectors. Systemic fungicides injected into the tree at 1–3 year intervals have proven beneficial in providing protection. An arborist should be consulted to discuss costs and potential benefits.
3. Remove diseased trees. Severe cases require complete removal of the tree. Wood should not be saved for firewood. It should be chipped to destroy the beetle’s breeding place. Nearby American elms may also be infected through root grafts. Destroying root grafts by mechanical severing can slow the spread of the disease, if done before the fungus has moved into healthy elm trees. This may not be practical in a home setting.
4. Replace diseased trees with varieties resistant to Dutch elm disease. The true Chinese elm, Ulmus parviflora, a tree with multi-colored bark, is one choice. A related tree with a vase shape similar to American elm is the Japanese zelkova, Zelkova serrata. Both are resistant to Dutch elm disease but not immune.
Symptoms and Diagnosis
Symptoms develop rapidly during a period of 4–6 weeks after leaves reach full size. The first visible symptoms are yellowing of foliage followed by wilting and browning, a condition called flagging. Usually a single branch is affected first; wilted branches die rapidly and leaves brown, curl, and often drop prematurely. The symptoms spread to nearby branches and then to one whole part of the tree. The entire tree finally wilts and dies. This progression of symptoms may develop in one season or may take several years. Positive diagnosis of the disease requires a laboratory test to culture the fungal pathogen.
Life Cycle
The fungus is primarily dependent on insectvectored transmission from tree to tree over long distances. There are 2 vectors for the fungus in North America, the native American elm bark beetle and the less prevalent European elm bark beetle. Both of these beetles feed and breed under the bark of living or recently dead elm trees or logs. They carry the spores of the fungus from infected trees and innoculate healthy trees as they feed. Both species of elm bark beetles are effective carriers. The cycle of infection by the fungus is tied to the life cycle of the vectors. The beetles breed in recently dead elm wood or weakened living trees. If the fungus is present in breeding sites, emerging beetles will carry spores to healthy elms and introduce the fungus in feeding sites on young twigs. The beetles can fly up to 1/4 mile in search of feeding or breeding sites, but they may be blown many miles by winds. The disease may also spread by root grafts from a diseased elm tree to a healthy elm tree provided that the root systems overlap.
Integrated Pest Management Strategies
1. There is no cure for the disease. If your elm tree has leaves yellowing or wilting on one or more branches, cut off several small branches and look for brown streaking in the sapwood. If brown streaking is evident, a laboratory test is suggested for positive identification. This disease may be confused with other canker and wilt pathogens of elm.
2. Maintain plant health. Provide adequate amounts of water and fertilizer. Mild cases of Dutch elm disease may respond to pruning of diseased wood if less than 5% of the tree is infected. Control the insect vectors. Systemic fungicides injected into the tree at 1–3 year intervals have proven beneficial in providing protection. An arborist should be consulted to discuss costs and potential benefits.
3. Remove diseased trees. Severe cases require complete removal of the tree. Wood should not be saved for firewood. It should be chipped to destroy the beetle’s breeding place. Nearby American elms may also be infected through root grafts. Destroying root grafts by mechanical severing can slow the spread of the disease, if done before the fungus has moved into healthy elm trees. This may not be practical in a home setting.
4. Replace diseased trees with varieties resistant to Dutch elm disease. The true Chinese elm, Ulmus parviflora, a tree with multi-colored bark, is one choice. A related tree with a vase shape similar to American elm is the Japanese zelkova, Zelkova serrata. Both are resistant to Dutch elm disease but not immune.
0
0
文章
Dummer. ゛☀
2017年09月19日
Crown gall is a plant disease caused by the soil-inhabiting bacterium, Agrobacterium tumefaciens. The bacterium causes abnormal growths or galls on roots, twigs, and branches of euonymus and other shrubs primarily in the rose family. The bacterium stimulates the rapid growth of plant cells that results in the galls. In addition to being unsightly, the galls weaken and stunt the growth of the plant. Although galls can disrupt the flow of water and nutrients up the roots and branches, they usually do not cause total plant death. The disease can spread to other susceptible plants through contaminated soil and tools. Most chemical treatments are not effective.
The galls on forsythia, viburnum, highbush blueberry, American elm, hickory, maple, oak, and privet are believed to be caused by a fungus, Phomopsis sp. Since its cultural controls are the same as for bacterial crown gall, both are treated together herein. Chemical treatments, however, will differ. Chemical treatments for both are of very limited value to the home gardener. Only those relating to bacterial crown gall have been addressed.
Symptoms and Diagnosis
Galls are most commonly found near ground level on the roots and lower branches of the plants. As the galls enlarge, they become woody and hard. The outer layer turns brown and corky. The plant may be weakened and stunted with some branch or tip dieback. Symptoms may not develop immediately after infection. Galls grow most rapidly during the warm months of the year.
Life Cycle
Crown gall forming bacteria inhabit the soil and survive for many years. The bacterium can initially be brought in on the roots of infected plants. It then spreads by soil and water movement or contaminated pruning tools. Bacteria enter the plant through wounds possibly caused by chewing insects, cultivation damage, or from grafting and pruning tools. The crown gall bacterium has been known to survive more than two years in the soil in the absence of susceptible plants. It can live for several years in decomposing galls buried in the soil. Crown gall is likely to be more serious in limed soil than in acid soils so soil pH could be important in limiting the disease.
Integrated Pest Management Strategies
1. Prune out infected material. Crown gall cannot be eliminated from a shrub even though the infected plant may live for many years. To improve the appearance of the plant, prune out and destroy infected stems below the galled area. Sterilize the pruning shears after each cut with a mixture of one part bleach to nine parts water.
2. Destroy infected plants. Destroy the infected plant. The bacterium will remain in the soil so it is important to plant a resistant plant species. If the same species needs to be planted in the area, remove and replace the soil or consider soil sterilization.
3. Sterilize the soil. Soils known to be infected with crown gall bacteria can be sterilized using chemicals, heat, or antibiotics. This is not practical for most home gardeners. A biological control has been introduced using a bacterium, Agrobacterium radiobactor strain 84. This bacterium was discovered to be antagonistic to crown gall bacterium. It is available for use as a preplant treatment by dipping nursery stock in a suspension of the live bacteria in water.
4. Exclude the problem. When purchasing forsythia and euonymus plants, inspect them carefully for signs of galls. Do not purchase plants that show gall-forming symptoms.
5. Replant with a more resistant plant species. The following plants recommended by the University of Illinois show greater resistance to bacterial crown gall: barberry, hornbeam, true cedars, ginkgo, golden raintree, tulip tree, mahonia, spruce, linden, boxwood, catalpa, beech, holly, larch, magnolia, black gum, pine, Douglas fir, bald cypress, hemlock, birch, firethorn, redbud, smoke tree, sweet gum, deutzia, serviceberry, yellowwood, yew, and zelkova.
The galls on forsythia, viburnum, highbush blueberry, American elm, hickory, maple, oak, and privet are believed to be caused by a fungus, Phomopsis sp. Since its cultural controls are the same as for bacterial crown gall, both are treated together herein. Chemical treatments, however, will differ. Chemical treatments for both are of very limited value to the home gardener. Only those relating to bacterial crown gall have been addressed.
Symptoms and Diagnosis
Galls are most commonly found near ground level on the roots and lower branches of the plants. As the galls enlarge, they become woody and hard. The outer layer turns brown and corky. The plant may be weakened and stunted with some branch or tip dieback. Symptoms may not develop immediately after infection. Galls grow most rapidly during the warm months of the year.
Life Cycle
Crown gall forming bacteria inhabit the soil and survive for many years. The bacterium can initially be brought in on the roots of infected plants. It then spreads by soil and water movement or contaminated pruning tools. Bacteria enter the plant through wounds possibly caused by chewing insects, cultivation damage, or from grafting and pruning tools. The crown gall bacterium has been known to survive more than two years in the soil in the absence of susceptible plants. It can live for several years in decomposing galls buried in the soil. Crown gall is likely to be more serious in limed soil than in acid soils so soil pH could be important in limiting the disease.
Integrated Pest Management Strategies
1. Prune out infected material. Crown gall cannot be eliminated from a shrub even though the infected plant may live for many years. To improve the appearance of the plant, prune out and destroy infected stems below the galled area. Sterilize the pruning shears after each cut with a mixture of one part bleach to nine parts water.
2. Destroy infected plants. Destroy the infected plant. The bacterium will remain in the soil so it is important to plant a resistant plant species. If the same species needs to be planted in the area, remove and replace the soil or consider soil sterilization.
3. Sterilize the soil. Soils known to be infected with crown gall bacteria can be sterilized using chemicals, heat, or antibiotics. This is not practical for most home gardeners. A biological control has been introduced using a bacterium, Agrobacterium radiobactor strain 84. This bacterium was discovered to be antagonistic to crown gall bacterium. It is available for use as a preplant treatment by dipping nursery stock in a suspension of the live bacteria in water.
4. Exclude the problem. When purchasing forsythia and euonymus plants, inspect them carefully for signs of galls. Do not purchase plants that show gall-forming symptoms.
5. Replant with a more resistant plant species. The following plants recommended by the University of Illinois show greater resistance to bacterial crown gall: barberry, hornbeam, true cedars, ginkgo, golden raintree, tulip tree, mahonia, spruce, linden, boxwood, catalpa, beech, holly, larch, magnolia, black gum, pine, Douglas fir, bald cypress, hemlock, birch, firethorn, redbud, smoke tree, sweet gum, deutzia, serviceberry, yellowwood, yew, and zelkova.
0
0
文章
Dummer. ゛☀
2017年09月19日
Unlike other blights, chestnut blight is not just associated with shoot dieback; it can kill twigs and branches of any size. It is actually a canker disease caused by a fungus, Cryphonectria parasitica, formerly known as Endothia parasitica.
The significance of chestnut blight is tied to the species it decimated- the American chestnut, Castanea dentata. In 1900 the American chestnut was not only the dominant species of eastern hardwood forests in the U.S., it was the most important tree commercially, because of its beautiful, rot resistant lumber, because of the quantities of edible nuts it produced, and because of the rapidity with which it could repopulate clear-cut areas of the forest.
Chestnut blight was first identified in the United States in New York City in 1904, but it probably entered the country earlier, in the late 1800s on imported Asian chestnuts. By 1950, 99.9% of American chestnuts were reduced to either dead stumps or stumps with adventitious sprouts arising from the roots surrounding them. Many of these stumps persist today and are still sending up diseased sprouts that are as susceptible to chestnut canker as the parent plant.
Other species that are highly susceptible to chestnut blight are the Allegheny chestnut (C. pumila), the bush chinkapin chestnut (C. alnifolia) and the European chestnut (C. sativa). The last species, Castanea sativa, is not native to the U.S. and is restricted here. Some oaks are host to the disease; these include live, post, scarlet and white oaks. It is also occasionally found on shagbark hickory, red maple and staghorn sumac.
Chinese and Japanese chestnuts have shown some resistance to chestnut blight; for these Cryphonectria parasitica is a stress pathogen only. No other species of chestnut, however, has the characteristics necessary to replace the American chestnut as a forest tree or as an ornamental. The European chestnut, Castanea sativa, does share some of these characteristics, but it is also susceptible to chestnut blight and its importation into this country is restricted.
Symptoms and Diagnosis
Obvious symptoms on the American chestnut include flagging (the yellowing and dying of individual branches) and dead leaves that hang onto branches over the first winter. On young trees and on juvenile branches of mature trees, cankers appear as yellowish to reddish areas in the bark around branch crotches; these cankers can girdle and kill a branch within a few weeks. On mature trees, cankers are initially imperceptible unless the bark is stripped off. Later, as the canker expands, the bark swells and cracks, eventually falling off. Yellowish brown fruiting bodies may be visible on the surface of the bark around the canker or in the cracks in the bark. In American chestnuts, the trunk is eventually girdled which can occur within a few weeks for young trees and within a few years for mature trees. Few last longer than four years. Suckers usually shoot up from the surrounding roots of American chestnuts providing a constant supply of susceptible tissue for the pathogen’s continued existence; this suckering does not occur in other species.
Live oaks decline slowly. Foliage at the crown is chlorotic and sparse with dead branches. Cankers are difficult to discern.
Severe dieback can occur on post oaks and scarlet oaks, but smaller cankers or superficial cankers are more common. Cankers on post oak are more pronounced than on live oaks and the bark will usually slough off, while on scarlet oaks the cankers appear swollen and remain covered with bark. Swelling can also indicate cankers on white oak.
Infected Chinese and Japanese chestnuts are usually stressed trees. Chinese chestnuts display twig or branch dieback or targetlike cankers, and bark will eventually slough off.
Buff to orangish flat, mycelial fans in the diseased bark are characteristic of chestnut blight although positive diagnosis of the disease requires a laboratory test to culture the fungal pathogen.
Life Cycle
The success of this disease must be attributed, as least in part, to its ability to spread in so many different ways. Vectors include insects, birds, other animals, wind, and rain. Ascospores or conidia enter fresh wounds, probably caused by insects, usually in bark surrounding branches and twigs. Buff to orange mycelial fans then spread into living bark and cambium tissue. As cell death occurs, the fungus spreads into living tissue. Thus, as branches and twigs are girdled, the canker moves toward living tissue–ultimately to the main trunk of the tree. It does not, however, invade the crown.
The environmental conditions necessary to the survival of the chestnut blight pathogen seem virtually unlimited. No condition in which a chestnut can live discourages or suppresses the pathogen. It can live anywhere chestnuts live and can reproduce at any time of the year.
Integrated Pest Management Strategies
1 There is no cure for chestnut blight. Once the pathogen is present in an area, and it is already present in most areas, any American chestnut is at extreme risk; therefore, do not plant them. Other species should only be planted in preferred growing conditions; stressed sites will place them at risk.
2. Choose resistant species. Although the search for a blight resistant American chestnut has been ongoing for nearly a century, no blight resistant American chestnuts are currently on the market. Specimens sold as "blight free" have not been exposed to the disease (i.e., blight-free does not mean blight resistant).
The significance of chestnut blight is tied to the species it decimated- the American chestnut, Castanea dentata. In 1900 the American chestnut was not only the dominant species of eastern hardwood forests in the U.S., it was the most important tree commercially, because of its beautiful, rot resistant lumber, because of the quantities of edible nuts it produced, and because of the rapidity with which it could repopulate clear-cut areas of the forest.
Chestnut blight was first identified in the United States in New York City in 1904, but it probably entered the country earlier, in the late 1800s on imported Asian chestnuts. By 1950, 99.9% of American chestnuts were reduced to either dead stumps or stumps with adventitious sprouts arising from the roots surrounding them. Many of these stumps persist today and are still sending up diseased sprouts that are as susceptible to chestnut canker as the parent plant.
Other species that are highly susceptible to chestnut blight are the Allegheny chestnut (C. pumila), the bush chinkapin chestnut (C. alnifolia) and the European chestnut (C. sativa). The last species, Castanea sativa, is not native to the U.S. and is restricted here. Some oaks are host to the disease; these include live, post, scarlet and white oaks. It is also occasionally found on shagbark hickory, red maple and staghorn sumac.
Chinese and Japanese chestnuts have shown some resistance to chestnut blight; for these Cryphonectria parasitica is a stress pathogen only. No other species of chestnut, however, has the characteristics necessary to replace the American chestnut as a forest tree or as an ornamental. The European chestnut, Castanea sativa, does share some of these characteristics, but it is also susceptible to chestnut blight and its importation into this country is restricted.
Symptoms and Diagnosis
Obvious symptoms on the American chestnut include flagging (the yellowing and dying of individual branches) and dead leaves that hang onto branches over the first winter. On young trees and on juvenile branches of mature trees, cankers appear as yellowish to reddish areas in the bark around branch crotches; these cankers can girdle and kill a branch within a few weeks. On mature trees, cankers are initially imperceptible unless the bark is stripped off. Later, as the canker expands, the bark swells and cracks, eventually falling off. Yellowish brown fruiting bodies may be visible on the surface of the bark around the canker or in the cracks in the bark. In American chestnuts, the trunk is eventually girdled which can occur within a few weeks for young trees and within a few years for mature trees. Few last longer than four years. Suckers usually shoot up from the surrounding roots of American chestnuts providing a constant supply of susceptible tissue for the pathogen’s continued existence; this suckering does not occur in other species.
Live oaks decline slowly. Foliage at the crown is chlorotic and sparse with dead branches. Cankers are difficult to discern.
Severe dieback can occur on post oaks and scarlet oaks, but smaller cankers or superficial cankers are more common. Cankers on post oak are more pronounced than on live oaks and the bark will usually slough off, while on scarlet oaks the cankers appear swollen and remain covered with bark. Swelling can also indicate cankers on white oak.
Infected Chinese and Japanese chestnuts are usually stressed trees. Chinese chestnuts display twig or branch dieback or targetlike cankers, and bark will eventually slough off.
Buff to orangish flat, mycelial fans in the diseased bark are characteristic of chestnut blight although positive diagnosis of the disease requires a laboratory test to culture the fungal pathogen.
Life Cycle
The success of this disease must be attributed, as least in part, to its ability to spread in so many different ways. Vectors include insects, birds, other animals, wind, and rain. Ascospores or conidia enter fresh wounds, probably caused by insects, usually in bark surrounding branches and twigs. Buff to orange mycelial fans then spread into living bark and cambium tissue. As cell death occurs, the fungus spreads into living tissue. Thus, as branches and twigs are girdled, the canker moves toward living tissue–ultimately to the main trunk of the tree. It does not, however, invade the crown.
The environmental conditions necessary to the survival of the chestnut blight pathogen seem virtually unlimited. No condition in which a chestnut can live discourages or suppresses the pathogen. It can live anywhere chestnuts live and can reproduce at any time of the year.
Integrated Pest Management Strategies
1 There is no cure for chestnut blight. Once the pathogen is present in an area, and it is already present in most areas, any American chestnut is at extreme risk; therefore, do not plant them. Other species should only be planted in preferred growing conditions; stressed sites will place them at risk.
2. Choose resistant species. Although the search for a blight resistant American chestnut has been ongoing for nearly a century, no blight resistant American chestnuts are currently on the market. Specimens sold as "blight free" have not been exposed to the disease (i.e., blight-free does not mean blight resistant).
0
0
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.
0
0
文章
Dummer. ゛☀
2017年09月19日
Ash yellows is a disease caused by Candidatus fraxinii, which affects the tree's vascular system or its’ phloem sieve tubes. It is presently only found in North America. Ash yellows disease cycle is still a mystery. Experts think it is transmitted by insect vectors such as leaf hoppers which also transmit viruses. Symptoms seem to appear most widely on white ash (Fraxinus americana) than green ash (F. pennsylvanica.) It can also affect at least ten other ashes including black ash (F. nigra) and blue ash (F. quadrangulata.) The ash yellows phytoplasma can also cause symptoms of witches broom in lilacs often called lilac witches broom.
Ash decline is the rapid decline of ash trees including sparse crown growth and dieback. It may be caused by many factors including environmental factors like weather stresses or poor soil conditions and other pathogens like ash yellows.
Symptoms and Diagnosis
Symptoms of ash yellows and decline can vary depending upon ash species and environment conditions.
White ash shows the most prominent of symptoms for ash yellows and can result in substantial dieback which leads to premature death of the trees. Trees may show slow twig growth and short internodes among the twigs causing a tufted appearance of foliage and thinning of the overall crown. The symptomatic leaves can be stunted, chlorotic (yellow coloring,) have upturned margins, and premature autumn color. When the branches are slow growing laterally, another symptom is deliquescent branches which lose their apical dominance. Additionally, the branches can have severe dieback. The tree may develop witches broom at the trunk collar and occasionally in major branches as well.
Green ash can have similar symptoms as white ash but usually less severe. Green ashes can develop witches broom at the base of the tree without the other symptoms. Green ash appears to tolerate ash yellows better than white ash.
Observation of the trees’ conditions is very important since adverse environmental conditions can cause similar decline in ash trees as ash yellows. Some environmental factors to look out for are mechanical damage, drought stresses, insect infestations, and parasitic fungi. The witches broom can be diagnostic of the ash yellows but this symptom is not always present with infected ash trees.
Ash decline can be caused by both ash yellows and other environmental factors, mentioned above. Ash decline is typified by growth reduction and crown dieback. Both ash yellows and environmental factors can work together to cause the premature death of the ash tree in as little as 2 years or as many as 10 years once symptoms occur.
Molecular method tests such as polymerase chain reaction (PCR) are available in diagnostic labs for the ash yellows phytoplasma. At this point, the presence of witches broom is the most reliable diagnostic symptom in the field but not all infected trees have them.
Integrated Pest Management Strategies
1. Remove the tree. There is no cure for ash yellows. Remove any trees that have severe dieback over 30 to 50% of the crown and decline since the tree will not recover.
2. Improve the vigor of the tree. Although there is no known cure for ash yellows or decline, improving the growing conditions of your tree by watering during drought or fertilizing the tree in the fall can help the tree to live longer and look better.
3. Choose trees suited to the growing conditions. Do not plant ash trees in drought prone areas and reduce competitive plants. Plant a diverse group of trees including other types of trees besides ash trees.
4. Plant more resistant trees. Plant other ash trees besides white and green ash. Some cultivars that have shown to be more resistant to ash yellows are Fraxinus pennsylvanica ‘Bergeson,’ ‘Dakota Centennial®’, ‘Patmore,’ and Fraxinus americana ‘Autumn Applause.’
Ash decline is the rapid decline of ash trees including sparse crown growth and dieback. It may be caused by many factors including environmental factors like weather stresses or poor soil conditions and other pathogens like ash yellows.
Symptoms and Diagnosis
Symptoms of ash yellows and decline can vary depending upon ash species and environment conditions.
White ash shows the most prominent of symptoms for ash yellows and can result in substantial dieback which leads to premature death of the trees. Trees may show slow twig growth and short internodes among the twigs causing a tufted appearance of foliage and thinning of the overall crown. The symptomatic leaves can be stunted, chlorotic (yellow coloring,) have upturned margins, and premature autumn color. When the branches are slow growing laterally, another symptom is deliquescent branches which lose their apical dominance. Additionally, the branches can have severe dieback. The tree may develop witches broom at the trunk collar and occasionally in major branches as well.
Green ash can have similar symptoms as white ash but usually less severe. Green ashes can develop witches broom at the base of the tree without the other symptoms. Green ash appears to tolerate ash yellows better than white ash.
Observation of the trees’ conditions is very important since adverse environmental conditions can cause similar decline in ash trees as ash yellows. Some environmental factors to look out for are mechanical damage, drought stresses, insect infestations, and parasitic fungi. The witches broom can be diagnostic of the ash yellows but this symptom is not always present with infected ash trees.
Ash decline can be caused by both ash yellows and other environmental factors, mentioned above. Ash decline is typified by growth reduction and crown dieback. Both ash yellows and environmental factors can work together to cause the premature death of the ash tree in as little as 2 years or as many as 10 years once symptoms occur.
Molecular method tests such as polymerase chain reaction (PCR) are available in diagnostic labs for the ash yellows phytoplasma. At this point, the presence of witches broom is the most reliable diagnostic symptom in the field but not all infected trees have them.
Integrated Pest Management Strategies
1. Remove the tree. There is no cure for ash yellows. Remove any trees that have severe dieback over 30 to 50% of the crown and decline since the tree will not recover.
2. Improve the vigor of the tree. Although there is no known cure for ash yellows or decline, improving the growing conditions of your tree by watering during drought or fertilizing the tree in the fall can help the tree to live longer and look better.
3. Choose trees suited to the growing conditions. Do not plant ash trees in drought prone areas and reduce competitive plants. Plant a diverse group of trees including other types of trees besides ash trees.
4. Plant more resistant trees. Plant other ash trees besides white and green ash. Some cultivars that have shown to be more resistant to ash yellows are Fraxinus pennsylvanica ‘Bergeson,’ ‘Dakota Centennial®’, ‘Patmore,’ and Fraxinus americana ‘Autumn Applause.’
0
0
