A variety of diseases can attack fruit trees. Agricultural Extension Agent Dr. Alan Windham discusses methods of coping. Some diseases begin their life cycle on entirely different plants--for example, a disease called cedar-apple rust, which spreads from red cedar (Juniperus virginiana ) and a few other junipers to apple trees. A fungal disease, cedar-apple rust overwinters on various juniper species. The spores emerge in spring to infect apple trees and travel on the wind. The best prevention is to plant resistant cultivars such as 'Red Delicious', 'Early McIntosh', 'Freedom', 'Granny Smith', 'Liberty', 'Northwestern Greening', 'Nova Easygrow', 'Priscilla', 'Redfree', 'Sharon' and 'Sir Prize'. Infected leaves develop bright yellow-orange spots and may drop prematurely; fruit from infected trees may have spots. Contact your local agricultural extension office to ask the names of fungicides that can be sprayed when the trees are vulnerable--from the pink stage of apple blossoms until petals drop. Susceptible trees should be sprayed regularly during this period. Bacterial spot may affect plums, cherries and other plants in the genus Prunus. Early signs include small pale-green to yellow spots on leaves; the spots may drop out, giving leaves a "shot hole" appearance that may resemble insect damage. Bacterial leaf spot can be prevented or minimized by planting resistant varieties. Black knot, a fungal disease, also affects cherries, plums and other species in the genus Prunus. Black swellings, or galls, may appear on branches and the main trunk. The galls produce spores that infects succulent green shoots in the spring. To control the disease, prune out all galls when the tree is dormant. Cut off infected shoots about 3" below the affected area. Put galls and cuttings in a plastic bag, and throw them away. It's also a good idea to get rid of any diseased wild plum or cherry trees growing nearby in fence rows or woods. Fire blight, a bacterial disease, kills new growth rapidly in the spring. The blight enters the tree at the branch tips and travels down the stems, causing dieback. It is spread by insects such as aphids and leafhoppers. Avoid heavy pruning or heavy applications of nitrogen fertilizer, both of which encourage abundant new growth. Control by pruning off branches 1' below the infected sections. Between each cut, dip pruners into alcohol or a 10 percent bleach solution to prevent spread of the disease. Another common problem for peach trees is peach-leaf curl, caused by a fungus. Affected leaves are curled and puckered and easy to distinguish from healthy ones. Spores may be spread to peach trees from fallen leaves; once the tree is infected, spores overwinter on the surfaces of peach twigs. To help control the disease, keep the soil around the base of the tree free from fallen leaves. When the tree is dormant, apply a Bordeaux mix, made from copper and oil, or a commercial fungicide to kill overwintering spores. Root diseases such as crown gall, caused by a bacterium, affect the base of the plant. When you buy dormant bare-root plants, inspect them for any sign of this disease. Once a plant is infected with this disease, it will never grow well, so the best cure is prevention. The bacteria live in soil for a long time, so new trees should not be planted where affected trees have grown. Fruit rots are caused by fungus. If your trees are affected by fruit rot, remove infected fruit to help reduce the spread of the disease. Dispose of infected fruit in a covered container: don't compost it. Remove any dead twigs attached to the fruit as well.
RESOURCES :
Organic Gardener's Handbook of Natural Insect and Disease Control
Rodale Press Inc. (Organic Gardening Magazine)
Emmaus, PA 18098
Phone: 610-967-5171
Fax: 800-813-6627
Email: customer_service@rodalepress.com
GUESTS :
Alan Windham
UT Agricultural Extension Service
5201 Marchant Drive
Nashville, TN 37211-5201
Phone: 615-832-6802
Fax: 615-832-0043
Email: awindham@cru.gw.utk.edu
Website: http://www.utextension.utk.edu
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