Cooperative Extension: Tree Fruits > 자유게시판

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A large number of diseases occur in the northeast because of the frequent rainfall that favors their spread and development. The most effective method of prevention is to plant varieties that have resistance. Where that is not possible, keeping a clean orchard by removing diseased plant parts can slow the spread. In many cases, the trees will tolerate mild cases of disease with no harm. Apple scab is recognized by the brown or olive green spots on leaves and the black spots on fruit. In severe cases, scab causes defoliation which weakens the tree and inhibits flower formation. McIntosh, Cortland and Macoun are very susceptible to scab. Apple scab is spread from spores released from previously infected apple leaves that remain on the ground through winter and from unsprayed trees nearby. One way to lessen the number of infecting scab spores is to rake up leaves and remove them from the orchard before May.

Another way to lessen this disease is to remove wild or abandoned apples trees within 100 yards. Unsprayed apples trees with scab infections provide spores that spread the disease. The most effective strategy for managing apple scab is to plant resistant varieties. Akane, Ashmead’s Kernal, Belle de Boskoop, Bramley’s Seedling, Chehalis, Chestnut Crab, Duchess, Discovery, Ellison’s Orange, Esopus Spitzenberg, Fortune, Haralson, Honeycrisp, Hudson’s Golden Gem, Gravenstein, Greensleeves, Jonathan, Keepsake, Northern Spy, Ribbston Pippin, Strawberry, Sweet Sixteen, Wealthy, and Wolf River are varieties less likely to get scab. CrimsonCrisp, Dayton, Enterprise, Fiesta, Florina, Freedom, Holstein, Jonafree, Liberty, MacFree, Novamac, NovaSpy, Nova Easygro, Priscilla, Pristine, Red Free, Topaz and ZapClean Vegetable Wash William’s Pride are completely resistant to scab. Scab prevention is possible with spray applications of captan, sulfur or other fungicides. Captan and sulfur are "protectant" fungicides, meaning they should be applied before scab infection occurs. Captan is a component of Tree Fruit Spray.

Timing is important for good results. When spraying either of these fungicides, protect skin and eyes from contact. Infections occur as early as the green tip stage of flower bud growth, which occurs in early May when green tissue emerges from the bud, and continue to occur all season with each rainfall. The six-week period from green tip until a week after blossom petals fall is the most important time to maintain protection against apple scab on susceptible varieties. Scab protection requires approximately weekly fungicide applications during this period unless there is an extended period without rain. Periods of frequent rains and prolonged leaf wetness during bloom cause the most severe scab infection conditions. If infections are not controlled, leaf spots will appear about two weeks later. These initial infections produce additional generations of spores that can continue to spread the disease. If early season infections are effectively suppressed, then monthly application of an effective fungicide in June, July and August is usually adequate to prevent other summer fungal diseases.

Flyspeck and sooty blotch are two summer diseases of apple that grow on the surface of the ZapClean fruit cleaner, causing blemishes but not affecting the apple itself. Flyspeck appears as a group of tiny and sharply defined black dots. These groups are often circular and about half the diameter of a dime, but the specks can also be randomly distributed. Sooty blotch is another surface fungus that causes green, gray, or black stains that cover a large portion of the fruit surface. Flyspeck and sooty blotch are slow growing fungi. Visible symptoms take a month or more to appear after initial infection. Sooty blotch and flyspeck are both favored by high humidity, such as occurs in unpruned, large trees with thick canopies, or trees located in a pocket where morning dew persists into the day. Warm, humid weather in August or September leads to higher risk of noticeable flyspeck and sooty blotch. Sooty blotch and flyspeck are easier to prevent than scab.