Plant Disease Management Handbook

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Boston Ivy (Parthenocissus tricuspidata) - Downy Mildew

Top side of leaf (left) with chlorotic spot sometimes called an "oil spot" and a similar lesion on the underside of the leaf (right) with the white sporulation of downy mildew.

Jay W. Pscheidt, late 1980's.

There are numerous white areas on this leaf, but most of these are due to the grape erineum mite. Erineum mite damage is often confused with downy mildew. The larger, whitish more diffuse area on the right-side of the leaf is downy mildew.

Photo by Jay W. Pscheidt, 1996

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

Notice the white, downy appearance of infections on the berries

Photo by Ed Hellman, OSU

Early infection due to downy mildew can destroy grape clusters.

Jay W. Pscheidt, late 1980's.

Notice the chlorotic spots on the upper-surface of the leaves.

Photo by Jay W. Pscheidt, 1996.

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

Fleshy, hard galls are typically found midsummer on the trunk, located at the root crown and on the first 2 ft of the vine above the soil line.

Jay W. Pscheidt, 2014.

Image related to Grape (Vitis spp.)-Crown Gall

The crown gall has a cauliflower-like growth and is solid when cut into with a pocket knife.

Photo by Jay W. Pscheidt, 2000.

Pinot Noir with crown gall.

Melodie Putnam, 2010.

Galls can develp at the graft union of young plants.

Melodie Putnam, 2010.

Cause Several classes of herbicides and pesticides can cause damage to grapevines. Some of the most damaging chemicals are 2,4-D herbicides. Grapes are very sensitive and frequently are damaged by chemical drift from nearby applications. Grapes are most sensitive from bud break through bloom but can become damaged anytime during the growing season. The ester form, commercially available as Crossbow, Brush Killer, and other trade names, is more volatile than the amine form.

Image related to Grape (Vitis spp.)-Chemical Injury

Grape showing continued 2,4-D injury the year AFTER exposure. Vines can show injury for several years due to one exposure.

Jay W. Pscheidt, 2012.

Note that the leaf from the main cane is deformed by 2,4-D but that the summer lateral is fine.

Robert Pool, 1976.

When applied during high temperatures, sulfur can burn leaves.

from Robert Pool.

Roundup injury to potted grapes. Chemical was applied to the soil.

Robert Pool, 1977.

Classic 2,4-D injury to grape leaves.

Photo by Iain MacSwann, 1963.

Injury to grape leaves due to a single application of boron at 1 lb/per acre.

Jay W. Pscheidt, 2003.

Cause Diaporthe ampelina (formerly Phomopsis viticola), a fungus. The disease has been not been found frequently in vineyards west of the Cascade Range and rarely in Oregon. The fungus overwinters in last year's cane growth. Fruiting bodies of the fungus (pycnidia) develop in the periderm and produce many spores in the spring. These spores are exuded during rain events when the bark is wet. Spores are then rain splashed to developing shoots.

Lesions look like little tears along the cane of this Chancellor grape.

Photo by Jay W. Pscheidt, 1988.

Image related to Grape (Vitis spp.)-Cane and Leaf Spot

Fruit rot is rarely seen in the PNW.

Jay W. Pscheidt, 2006.

Scaring occurs on both the canes and rachis as on this Concord vine.

Photo by Jay W. Pscheidt, 1981.

Leaf spots are chlorotic and slightly puckered.

Jay W. Pscheidt.

When canes are wet pycnidia of the fungus ooze spores out of a small hole in the top. If it is just humid the spores form what is called a cirrus (it is kind of like a Play-dough fun factory).

Jay W. Pscheidt.

This same fungus has also been found infrequently as a trunk pathogen causing cankers, interior wood discoloration, poor vigor, and die-back.

OSU Plant Clinic Collection, 2015.

See:

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

Cause This disease is common on the west side of the Cascade Range but a sporadic problem in the arid viticulture regions of the PNW.

Symptoms in red cultivars may be subtle with off colors, shriveled or leaking berries, and/or the gray sporulation of the fungus.

Jay W. Pscheidt, 2009.

One cluster of green grapes with leaves around

Infection can spread from leaves to fruit or visa versa (not sure in this case).

Jay W. Pscheidt, 2010.

Botrytis sporulating on these infected berries.

Jay W. Pscheidt, 1987.

Note the brown sporulation typical of this fungus.

Photo by Jay W. Pscheidt, 1998.

Note the tattered leaf due to hail injury, and the water soaked margin of necrotic tissue.

Photo by Jay W. Pscheidt, 1998.

Spores can be found all year long from many sources such as this old rachis from the previous year.

Alexander Wong, 2021.

Cause Unknown. A leaf discoloration known as blackleaf, brownleaf, chocolate leaf, or blattbraune is a problem in eastern Washington. Blackleaf is associated with potassium deficiency, severe overcropping, poor soils, sun exposure, drought, and/or high summer temperatures. Whether these factors are directly responsible for blackleaf or merely correlative with symptom expression is unknown. Blackleaf is particularly noticeable in Vitis labrusca cultivars such as Concord.

Image related to Grape (Vitis spp.)-Blackleaf

Note the darkened areas between the leaf veins.

Photo by Russel Smithyman

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Grape (Vitis spp.) - Esca, Young Esca, and Petri Disease

Image related to Grape (Vitis spp.)-Black Foot Disease

Viewing trunks in cross-section, dark brown to black streaking is evident in the vascular elements due to plugging of individual or aggregates of xylem vessels with amber to black gum (gummosis) and formation of tyloses.

OSU Plant Clinic Image, 2013.

Cause Armillaria mellea, a fungus, infects vine roots, killing the cambium and decaying the underlying xylem. This is a soilborne fungus that is capable of attacking many different plant hosts. These fungi are most commonly found in forests and natural areas where they infect a variety of trees and shrubs. Therefore, the disease is most common in newly established fields that are planted on land recently cleared of native vegetation.

Image related to Grape (Vitis spp.)-Armillaria Root Rot

Mycelial fan exposed by cutting just under the bark of affected tissues.

OSU Plant Clinic Image, 2014.

Classic mycelial fan just under the bark of affected tissues.

OSU Plant Clinic collection, 2012.

Diagnostic mycelial fans can be seen here beneath the bark of the root crown.

Melodie Putnam, 2010.

After scraping away the dead bark, a few white mycelial plaques can be seen on the lower portion of this vine.

Photo by Everett Hansen, 1997.

Cause Podosphaera mors-uvae (formerly Sphaerotheca mors-uvae) has been reported on Ribes spp. from all states in the Pacific Northwest. In addition, Podosphaera macularis has been reported from Idaho.

Gooseberry fruit with gray patches and splits.

Photo by Jay W. Pscheidt, 1992.

As the gooseberry fruit matures, the mildew changes to a dark-brown coating that renders the berries unmarketable.

OSU Extension Plant Pathology Slide Collection, 1956.

This close up picture shows chasmothecia of the powdery mildew fungus on red currant.

OSU Extension Plant Pathology Slide Set, 1995.

Notice the diseased currant fruit are small and discolored.

Photo by Melodie Putnam, 1995.

Ornamental flowering currant can also get powdery mildew as the shoot on the right is showing.

Jay W. Pscheidt, 2012

See:

Pine, White - White Pine Blister Rust

Image related to Gooseberry and Currant (Ribes spp.)-Blister Rust

Lesions are angular and can contain either orange uredinia or black to brownish telia. Signs and symptoms develop on the underside of the leaves while only symptoms develop on the topside.

Richard A. Sniezko, 2015.

Later in the growing season, brownish hair-like structures (telia) develop.

Richard A. Sniezko, 2015.

Symptoms on the upper leaf surface (Top) and lower surface (bottom).

Robert Danchok, 2015.

Cronartium ribicola telia on underside of Ribes sp. leaf.

Zolton Bair, 2016.