Armillaria root rot
Armillaria root rot affects many woody plants, including grapes. Vineyards planted on old orchard sites or newly cleared forestland may be at risk. Aboveground symptoms are stunted shoots, yellow or red leaves, wilting and premature defoliation. Symptoms are most obvious in late summer, when vines may completely collapse and die. White, feltlike fungal mats occur below the bark near the soil line.
Infected tissues have a distinct mushroomlike odor when moist. Black, shoestringlike strands (rhizomorphs) may be present on bark and in the soil. In the fall, clumps of golden-brown mushrooms may appear at the base of the vine.
The fungus spreads to neighboring vines via root contact and rhizomorphs, resulting in distinctive clusters of dead vines within the vineyard. Armillaria can survive for years on dead roots and old tree and vine stumps in the soil.
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