Plant Disease Management Handbook

Cause Pierce's Disease, (Xylella fastidiosa subsp. fastidiosa),which has been a high-profile and rapidly increasing disease in California, and other Southern States, is not known to be in the Pacific Northwest. Our climate may be too cold for the pathogen to survive. Infected grapevines do not retain the pathogen after a cold dormant-season typical of continental climates. The disease is in Florida and Texas and can be very damaging.

Cause Meloidogyne hapla (northern root-knot nematode) is a sedentary endoparasite of which only second-stage juveniles (the infective stage) and adult males (which may be rare) are in soil. Juveniles move in the water film on soil particles and invade the root tip. They move through the root and locate a parenchyma cell in the root cortex. The feeding modifies the cell to form a large specialize feeding cell called a giant cell.

Cause Mesocriconema xenoplax, an ectoparasite which gets its common name from the cuticular ring ornamentation around its body. The nematode moves slowly as it browses along the root and may feed at one site up to 7 days. It feeds from outside of the root by inserting a stylet into an individual root cortical cell. Ring nematode does not disrupt the cell membrane during feeding, but alters the sink strength of the punctured cell and those cells surrounding it, allowing for greater metabolic activity.

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Grape (Vitis spp.) - Virus Diseases

See:

Grape (Vitis spp.) - Virus Diseases

Grape (Vitis spp.) - Grapevine Red Blotch Disease

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Rhododendron - Lime-induced Chlorosis

Cause A physiological problem that has not been explained fully. Frequent attempts to isolate pathogens from necrotic tissue have not resulted in any fungi or bacteria. The disorder is associated with cool and/or wet weather just before bloom. Excessive vigor, shade just before bloom, and general stresses have also been associated with symptoms. The disorder resulted in low yields 4 out of 10 years in the 1980s in Oregon.

By R. Martin and J. Pscheidt

See

Grape (Vitis spp.) - Virus Diseases

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Grape (Vitis spp.) - Botryosphaeria Dieback

Grape (Vitis spp.) Relative Disease Susceptibility and Sensitivity to Sulfur

Cause Many fungi have been associated with these diseases, although the cause of esca continues to be disputed. Esca (black measles) is considered a disease of older vines.