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Armillaria root rot (ARR) disease in grapes is caused by the fungus Armillaria mellea that infects grapevine roots, killing the cambium, and decaying the underlying xylem. ARR is native to many regions and can infect hundreds of woody plants. Host plants include broad-leaved trees in oak woodlands and stands of conifers. Agronomic hosts include stone fruits, nut trees, currants, gooseberries, nut trees, roses, strawberries, and other rosaceous plants such as raspberries. Peaches, nuts and almonds are much more susceptible to ARR than grapes.
Exposure of the crown area of vines with Armillaria root rot reveals white mycelial fans of Armillaria mellea.
Photo credit: Jack Kelly Clark.
Vines infected with Armillaria root rot become nonproductive and often die within 2 to 4 years after the first appearance of symptoms, which typically start as a slight stunting of shoots that progresses each year. Severe symptoms include shorter canes with dwarfed and chlorotic leaves. Adjacent vines often become infected as well. The pathogen forms a white mycelial mat under the bark at or below the soil line. These structures can often be observed in symptomatic vines by digging down about a foot below the soil line and removing thin layers of bark from the root collar.
The trunk below the mat is often visibly rotted, with a soft, spongy consistency and light brown color, as compared to white, dense wood on the portion of the trunk that has no sign of the pathogen. This fungus may form mushrooms at the base of infected vines that produce wind-blown spores, but these spores are not a significant means of infection to healthy vines. The fungus spreads vegetatively below ground. The fungus can survive on woody host roots long after the host dies. When infected plants are removed, infected roots that remain below ground serve as a source of inoculum for vines planted in the same location. Healthy grapevine roots become infected when they come in contact with such inoculum. The fungus is favored by soil that is continually damp during the growing season.
What a grower can do?
The best management strategy is to remove residual roots before vineyard establishment. In diseased vineyards or sites supporting woody plants, use deep ripping to bring thick, woody roots and root crowns to the surface and then remove. This sanitation measure is much more efficient than fumigation alone. There are no known Armillaria-tolerant grape rootstocks. If possible, avoid planting sites infested with Armillaria. For chemical control follow the link to the Southern Region Small Fruit Consortium Bunch Grape Integrated Management Guide
Extension Fruit Crops Specialist
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