ARMILLARIA ROOT ROT

Authors: Baumgartner, Kendra; RIZZO, DAVID - UC DAVIS, PLANT PATH

Submitted to: Compendium
Publication Type: Book / Chapter
Publication Acceptance Date: 2/10/2004
Publication Date: 7/26/2004
Citation: Baumgartner, K., Rizzo, D.M. 2004. Armillaria Root Rot. In: Wilcox, W.F., et al. Compedium of Grape Diseases, 2nd edition. American Phytopathological Society Press. St. Paul, Minnesota. In Press.

Interpretive Summary: Armillaria mellea, causal agent of Armillaria root rot, infects grapevine roots, killing the cambium and decaying underlying root wood. The common occurrence of Armillaria root rot on grapevines and orchard trees planted on sites previously inhabited by oaks in California has been known since the disease was first descrived in the 1880s. However, it occurs on the roots of many common forest tree species in California. Symptoms include stunted shoots, dwarfed leaves, wilting, premature defoliation, and raisining of berries. Armillaria root rot occurs in circular patches in a vineyard that expand radially over time, which is due to the belowground vegetative spread of the fungus. Armillaria mellea is present on a site before a vineyard is established. It can survive on woody host roots long after the host dies by decomposing the root wood for nutrients. After land is cleared of diseased forest trees or orchard trees, any infected roots that remain belowground serve as a source of innoculum. Infection occurs when grapevine roots come in direct contact with partially decayed tree roots and are colonized by A. mellea vegetative fungal tissue. The best way to control Armillaria root rot is to remove partially decayed tree roots from the soil before planting and/or fumigating the soil to the maximum depth possible. For postinfection control on moderately symptomatic grapevines, root collar excavation may prevent mycelial fans from girdling the trunk. Dead and severely symptomatic grapevines should be removed and replanted after soil is thoroughly cleared of infected roots.

Technical Abstract: Armillaria mellea (Vahl:Fr.) P. Kumm., causal agent of Armillaria root tot, infects grapevine roots, killing the cambium and decaying underlying xylem. The common occurrence of Armillaria root rot on grapevines and orchard trees planted on sites previously inhabited by Quercus species (oaks) in California has been known since the disease was first described in the 1880s. However, it occurs on the roots of many common forest tree species in California. Symptoms include stunted shoots, dwarfed leaves, wilting, premature defoliation, and raisining of berries. Armillaria root rot occurs in circular patches (disease centers) that expand radially over time, which is due to the belowground vegetative spread of the fungus. Armillaria mellea is present on a site before a vineyard is established. It can survive on woody host roots long after the host dies by decomposing the root wood for nutrients. After land is cleared of diseased forest trees or orchard trees, any infected roots that remain belowground serve as a source of innoculum. Infection occurs when grapevine roots come in direct contact with partially decayed tree roots and are colonized by A. mellea mycelium. The best way to control Armillaria root rot is to remove partially decayed tree roots from the soil before planting and/or fumigating the soil to the maximum depth possible. For postinfection control on moderately symptomatic grapevines, root collar excavation may prevent mycelial fans from further root collar decay, thereby prolonging the life of infected grapevines. Dead and severely symptomatic grapevines should be removed and replanted after soil is thoroughly cleared of infected roots.