- Crown gall, caused by the Agrobacterium tumefaciens pathogen, displays as a distinct, abnormal growth on a walnut tree. This fungal disease shows itself at or below the soil's surface on the tree's base or roots. The gall is the result of the fungus stimulating the tissue cells of the walnut to mutate and produce a growth that becomes a living part of the tree. Crown galls are soft and spongy to the touch.
- Bacteria living in the soil surrounding the tree enter through wounds. Younger trees, those less than 10 years of age, are especially susceptible. To minimize the economic cost of treatment, growers may remove trees less than 4 years of age that display crown gall. Treat the gall by cutting it away or using a bactericide in the spring as new tree growth occurs.
- Canker is a fungal disease that occurs on branches and trunks. It causes a growth resembling a sunken, blackened depression surrounded by a raised growth of callused tissue. A wet seepage from within the bark of the tree and dark stains or streaks usually accompanies the canker. When the bark is removed from an infected area, intensely discolored wood is seen. The canker prevents other sections of the tree from receiving water and nutrition.
- Thousand cankers disease is a virulent strain of canker that primarily attacks black walnut trees. The disease is the result of a partnership between the Geosmithia canker fungus and the black walnut twig beetle (Pityophthorus juglandis). The fungus develops within dead or dying walnut trees and is transferred to healthy specimens by the twig beetle. Yellow, brown or wilted foliage displays from the top of the walnut tree downward. Thousand cankers disease is capable of killing a black walnut within 1 year.
Crown Gall
Gall Management
Canker
Thousand Cankers Disease
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