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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Leaf spot is a common descriptive term applied to a number of diseases affecting the foliage of ornamentals and shade trees. The majority of leaf spots are caused by fungi, but some are caused by bacteria. Some insects also cause damage that appears like a leaf spot disease. Leaf spots on trees are very common and generally do not require spraying. Leaf spot may result in some defoliation of a plant. An established plant can tolerate almost complete defoliation if it happens late in the season or not every year. Small or newly planted trees that become defoliated are more at risk of suffering damage until they become established.
Symptoms and Diagnosis The chief symptom of a leaf spot disease is spots on foliage. The spots will vary in size and color depending on the plant affected, the specific organism involved, and the stage of development. Spots are most often brownish, but may be tan or black. Concentric rings or dark margins are often present. Fungal bodies may appear as black dots in the spots, either in rings or in a central cluster. Over time, the spots may combine or enlarge to form blotches. Spots or blotches that are angular are generally referred to as anthracnose (see entry on “Anthracnose of Trees”) Leaves may yellow and drop prematurely.
Life Cycle The organisms that cause leaf spots survive in fallen infected leaves and twigs. Some may remain in dead twigs on the tree. Most damage occurs in spring. During wet weather, spores may splash or be windblown onto newly emerging tender leaves where they germinate in the moisture and infect the leaf. Overhead watering can also provide prolonged wet periods that are ideal for spreading leaf spot diseases.
Integrated Pest Management Strategies 1. Live with the disease. Most trees tolerate leaf spots with little or no apparent damage. A tree affected early in the year will re-leaf and the new leaves may not be affected. Only if defoliation occurs three or more years in a row will most established plants be adversely affected. 2. Remove infected leaves and dead twigs. Raking up and disposing of infected leaves as they drop and pruning out dead twigs can help control the disease by removing spores that can reinfect the new leaves. This is not a cure but may help limit infection by reducing the total amount of inoculum.
3. Keep foliage dry. Avoid overhead watering. Use soaker hoses or water early in the day so the foliage can dry off before night. Watering can also spread the disease by splashing. Pruning plants to allow for good air circulation and reducing crowding will also help keep the foliage dry. 4. Keep plants healthy. Since most plants can tolerate some defoliation, keep them in good health so they can rebound quickly. Avoid over fertilizing by testing the soil first. Abundant, young, tender growth is very susceptible to attack by disease and insects. Overuse of nitrogen can cause an abundance of succulent growth.
5. Use fungicides if needed. In rare cases of severe infection and where the size and value of plants make it practicable, applications of fungicides may be helpful. Sprays will not cure infected leaves. Therefore, once the damage is noticed, spraying may have limited value. Spraying generally needs to be started as buds break in the spring and repeated at 10–14 day intervals. Recommendations will vary by disease and fungicide used. Have the disease identified before purchasing a control product. 6. Replace the plant. Though a drastic measure, many gardeners find it less bother and more rewarding to replace a plant that is continually plagued with leaf spot diseases. Either replace with a different kind of plant or a variety that is more resistant or tolerant of disease. A nursery can help you in your selection.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Chlorosis is a general term that refers to the symptoms of uniform yellowing of leaves. It may be caused by any number of stresses including: nutrient deficiency, root damage, temperature extremes, herbicide misapplication, too much light, too little water or too much water, insect feeding, or disease pathogens.
Iron chlorosis is a common form of chlorosis. It is the result of a lack of iron in the new growth of the plant. Iron is not necessarily deficient in the soil—it may be there, but just in an unavailable form for absorption through the root system. Symptoms and Diagnosis The leaves of affected plants turn uniformly yellowish-green; or very commonly, they turn yellow between the veins, but the veins remain green. Yellowing is most common on new growth. The new growth may be stunted. In severe cases, leaves may die and drop prematurely. Twigs and branches may experience stunting and dieback, and plants may fail to produce flowers or fruit.
Yellowing is fairly certain to be due to iron chlorosis if the leaf veins remain green on the otherwise yellow leaf, and the chlorosis appears first on the younger or terminal leaves, spreading later to the lower parts of the plant. Iron chlorosis is most common on pin oak, sweet gum, and river birch trees as well as rhododendrons and azaleas. Integrated Pest Management Strategies 1. Monitor the problem. Many factors can cause leaves to become chlorotic. Therefore, before assuming the problem is lack of iron, have the problem diagnosed. Weather conditions and extreme changes in soil moisture may induce temporary symptoms of yellowed leaves. These symptoms may disappear as conditions normalize. Persistent chlorosis, however, needs attention. Plants commonly associated with chlorotic symptoms include holly, hydrangea, apple, blackberry, blueberry, cherry, grape, arborvitae, birch, boxwood, lilac, rhododendron, azalea, sweet gum, pin oak, and other oaks.
2. Use a foliar feeding for temporary results. Spraying the foliage with an iron compound will correct leaf chlorosis temporarily. Iron sulfate, iron chelate, and soluble organic iron complexes are used. Spraying will not affect leaves produced later in the season. Several sprays at intervals of 2 or 4 weeks may be needed to keep developing foliage green. The corrections will last only one season and will not change the underlying deficiencies that are soil-related. 3. Give your plants good growing conditions. Longterm correction of iron chlorosis requires good soil. Improve the soil surface by mulching with 2–4 inches of organic materials such as leaf mulch or compost. Also, ensure good drainage. The soil pH should be measured with a soil test. An alkaline soil is often the cause of iron chlorosis because it limits the solubility of iron in soil water.
4.Adjust the soil pH to make the iron available.The best long-range solution for correcting iron chlorosis in soils that are too alkaline is to make the soil more acid by lowering the soil pH. A pH of 6.0 to 6.5 is desirable for most plants. As low as 4.5 is recommended for azaleas, rhododendrons, and blueberries. The soil can be made more acid by the addition of sulfur, aluminum sulfate, or iron sulfate. Iron chelates, ferrous sulphate, aluminum sulphate, or sulfur can simply be spread on the soil surface and allowed to dissolve into the soil by watering and rainfall. This method requires more material, but is practical and feasible for the home gardener and may last several seasons, though the initial results are slow. Quicker effects may be seen if the chemicals are worked into the soil taking care not to cultivate too deeply so as to damage plant roots. Another method is to use water-soluble materials which can be injected into the soil with a root feeder.
An excellent technique for solving chlorosis problems has been developed by Dr. Carl Whitcomb of Lacebark Inc in Stillwater, Oklahoma. His directions from his website are included here with his permission Solving Chlorosis Problems and Total Nutrition for Trees. 5. Trunk implantation and injection. Implanting or injecting an iron chelate or iron sulfate directly into the trunk of the tree through holes is often effective in 10-30 days and may be effective up to 4-5 years, for iron sulfate some arborists report, before retreatment is needed. This method is employed by professional arborists and is quick, neat, and safe. However, it is only used when the plant has little or no dieback as a result of iron chlorosis.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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).
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Bacterial wetwood, also known as slime flux, is caused by an infection of one or more of several bacteria. It results in a water-soaked, oozing or bleeding condition of wood, which occurs in the trunk, branches and roots of shade and ornamental trees. It is normally not serious in most trees but is a chronic disease, which causes concern and can contribute to a general decline in tree vigor over time. Trees most susceptible to the disease include: elms, apple, crabapple, London plane, redbud, aspen, dogwood, magnolia, Russian olive, beech, fir, maple, sour gum, birches, hemlock, mountain ash, sycamore, boxelder, hickory, mulberry, sweet gum, butternut, horse chestnut, oaks, tulip tree, cottonwood, linden, pines, black locust, poplar, willow and walnut.
Symptoms and Diagnosis Symptoms vary with geographical location suggesting that the environment influences disease development. Trees in the western United States show more variability in internal disease development with much less bleeding and symptom expression than trees in the East and Midwest. Wetwood appears internally in the trunk and large limbs as a dark brown-black water-soaked area when the area is sectioned. The first external sign of wetwood is usually bubbling and seepage from wounded tissue in V-shaped branch crotches, wounds made by removal of branches, injection holes and trunk cracks. Insects are often attracted to the ooze on which they feed but there is not any evidence that these insects cause damage or transmit the bacteria but it is believed that some wood boring insects such as beetles may transmit the disease.
Life Cycle Organisms, most commonly bacteria, infect the tree deep in the tissue and start a process of fermentation. The resulting pressure (up to 60 psi) forces the bacterial ooze out cracks, branch stubs and pruning cuts. This ooze discolors bark, kills the cambium near the cut preventing proper callusing of wounds and kills grass and other plants on which it drips. Bacterial wetwood is noticed externally when it exudes slime and leaves a stain on the bark. Wilting of foliage is common in young trees; old trees are more likely to develop a general decline in vigor or branch dieback in the upper crown.
Integrated Pest Management Strategies 1. There is no cure or preventive treatment to avoid infection and development of bacterial wetwood. The following strategies may help. 2. Fertilization. Fertilize stressed trees to stimulate vigorous growth and lessen the severity of the disease but refrain from over fertilizing healthy vigorous trees as this may increase their susceptibility to the disorder.
3. Pruning. Remove any dead and weak branches. Promptly remove any loose or diseased bark around the area and make a clean cut arround wounds to facilitate healing. It is advided to disinfect tools with 70% rubbing alcohol before pruning a tree. Inserting a drainage tube to drain the area is not recommended. Insertion of a drainage tube can spread the disease and result in more harm than good.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
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.’
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Dummer. ゛☀
2017年09月19日
Dummer. ゛☀
Anthracnose is a group of related fungal leaf and stem diseases that infect shade trees. Maple anthracnose is not the same disease as oak anthracnose, although the symptoms of these diseases may be quite similar. Anthracnose diseases generally infect the leaf veins and cause death of the vein and surrounding tissue. Control of anthracnose diseases follows the same procedure for all shade trees affected. The disease does not cause the death of the host but may reduce growth over successive seasons of complete defoliation.
Symptoms and Diagnosis Irregular, light brown spots of dead tissue develop along the veins of the leaves. Affected plants may have the appearance of being sun-scorched. Sunken cankers containing fungal spores develop on infected twigs of some trees, such as sycamore. Life Cycle Anthracnose fungi overwinter on fallen leaves and twigs that were infected the proceeding year. Infection is favored by cool, moist weather in the spring of the year. Infection can occur on the vulnerable young leaves when there is a film of water on the leaf surface. Infection is typically more severe on the lower third of the tree, where the humidity is the highest.
Integrated Pest Management Strategies 1. Collect and destroy infected leaves as they fall. Infected leaves and twigs that remain in the vicinity are a source of spores for new infections in the spring. 2. Prune out dead branches. Be sure to clean all garden tools to avoid the spread of the disease. A 1–part bleach to 9–part water solution can be used to dip tools into between cuts. 3. Promote air circulation. Thin out excessive twig and branch growth. This will reduce the period of time that leaves are wet and vulnerable to inoculation.
4. Keep trees growing vigorously. Supply 1–2 inches of water weekly only during dry periods. Fertilize early in the spring or in late fall. 5. Spray with a fungicide when leaves are beginning to enlarge from the buds. Reapply at 7–10 day intervals for two or three more times. Fungicide sprays are most appropriate for younger, newly transplanted trees that may not be able to withstand defoliation. The available fungicides are preventive, not curative, and therefore, must be applied before spotting occurs. Commonly used products include copper, chlorothalonil (Daconil), captan, ferbam, mancozeb, maneb, and thiram. Your pesticide choice should be based on the particular problem you are seeking to control. Consult an arborist for difficult situations and where power equipment is required.
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