Plant Disease Management Handbook

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Grape (Vitis spp.) - Grapevine Red Blotch Disease

The discolored areas on the leaves expand and coalesce with time to become reddish or reddish-purple blotches that are strikingly apparent towards the end of the season. Although this leaf may be confused with the virus disease leafroll, it tested negative for leafroll and positive for red blotch.

OSU Plant Clinic Image, 2013.

Symptoms of red blotch on Pinot Noir (upper two images) from Willamette Valley and Merlot (lower two images) from Rogue Valley.

Bob Martin, 2014 and 2016.

Notice the leafroll symptoms on the leaves.

OSU Extension Plant Pathology Slide Collection, 1969.

Image related to Grape (Vitis spp.)-Virus Diseases

Mid-season leafroll symptoms on young vines, following a period of drought stress.

Photo by Ed Hellman, OSU

By M. Moyer

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Grape (Vitis spp.) - Botrytis Bunch Rot

Typical symptoms include a brown discoloration of the fruit and wet or oozing berries, coupled with the smell of vinegar and the presence of fruit flies.

Larry Moore collection, 1982.

Cause Short shoot syndrome (SSS), a term coined by the Oregon wine grape industry, describes a vine condition where shoots are severely stunted early in spring. Research conducted in Oregon and other cool climate grape growing regions worldwide have shown a relationship of this specific type of stunting with presence of grape rust mites (Calepitrimerus vitis). Other factors can cause stunting of shoots.

Image related to Grape (Vitis spp.)-Short Shoot Syndrome

The top two shoots have the shortened symptom compared to the lower shoot of the same age.

OSU Plant Clinic collection, 2012.

Close up of the shortened internode length of this shoot.

OSU Plant Clinic collection, 2012.

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Apple (Malus spp.) - Replant Disease

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

On the fruit, the fungus at first may appear grayish or whitish, but later has a brownish russeted appearance.

Jay W. Pscheidt, 2017.

Powdery mildew is best seen on leaves with incidental lighting (with the sun at an angle), in full sunlight with the sun over your shoulder.

Jay W. Pscheidt, 2011.

Image related to Grape (Vitis spp.)-Powdery Mildew

Using low power magnification you can see upright threads with chains of spores that look like a row of tiny water droplets or a short string of tiny pearls.

David Gadoury.

Flag shoots may be white to gray, deformed and/or delayed in bud break.

Walt Mahaffee.

Powdery mildew can often be seen on green fruit well before verasion.

Jay W. Pscheidt, 2017.

Scout for powdery mildew on escaped vines that may be in the fence rows near the vineyard. Leaves on this fence row vine had powdery mildew (lower left image).

Jay W. Pscheidt, 2018.

The white cast to the vines on the right are due to powdery mildew. Other vines have been treated with various fungicides.

Photo by Jay W. Pscheidt, 1995

The first mildew colonies generally can be found on the underside of leaves as very small diffuse spots.

Haywood Photography, 2005.

An early start to the epidemic can destroy clusters before bloom.

Haywood Photography, 2005.

Powdery mildew can be found on green canes as feathery dark patches.

Jay W. Pscheidt, 2000.

Cleistothecia squashed open to show several asci with ascospores.

Photo by Melodie Putnam, 1998.

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.

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Grape vines show general water stress with marginal necrosis on the leaves.

Jay W, Pscheidt, 2002.

Irregular periderm formation along the cane is a good symptom of Pierce's disease.

Jay W, Pscheidt, 2002.

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.