Plant Disease Management Handbook

Cause Puccinia brachypodii var. poae-nemoralis, a fungus that infects Kentucky bluegrass and survives as mycelium from season to season in infected foliage. Primary inoculum is urediniospores produced in pustules on overwintering sources; secondary inoculum is produced in pustules from primary infections. Several urediniospore cycles can occur in a growing season. Teliospores are two-celled and develop with urediniospores in fall; they often are covered by epidermis.

Cause A fungus, Gloeotinia temulenta, that lives in infected grass seed. Over 40 species of grass are susceptible. The disease is most common in annual ryegrass, perennial ryegrass, and tall fescue. In spring, the fungus emerges as stalked, cup-shaped apothecia (one to several per seed). Ascospores are ejected from the apothecia into the air; only those that land on flowers of a susceptible grass host will infect.

Cause A fungus, Sordaria sp., that is commonly found in the feces of herbivores. It is not considered a pathogen of grass or other plants. It showed up in Oregon seed fields during 2011 in areas of fields treated with high rates of chicken litter under unusually warm and wet early fall conditions. The fungus produces masses of black ascospores, which can coat leaf blades.

Cause Barley yellow dwarf virus (BYDV) infects many cultivated and wild grasses, including tall fescue, Chewing's fescue, ryegrass, orchardgrass, and bluegrass.

Image related to Grass for Seed-Barley Yellow Dwarf

Close-up of tall fescue plant infected with Barley yellow dwarf virus.

Photo by C. M. Ocamb, 2007

Perennial ryegrass field with circular patches of yellowing plants due to barley yellow dwarf.

Photo by C. M. Ocamb, 2007

Close-up of perennial ryegrass plant infected with Barley yellow dwarf virus.

Photo by C. M. Ocamb, 2007

Cynthia Ocamb, 21 May 2013

Cynthia Ocamb, 5 December 2013

Cynthia Ocamb, 22 Nov 2013

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Lawn and Turf

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Grape (Vitis spp.) - Leafroll

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 is 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.