Phomopsis cane and leaf spot disease, once known as “dead-arm”, is caused by the fungus Phomopsis viticola. Economic damage to grapevines occurs through loss of fruit from infections to the cluster rachis (main axis of a cluster). The rachis can become girdled by lesions causing berries below the lesions to shrivel. The rachis also becomes brittle and portions of the cluster may break off before harvest. Fruit infections can also occur, causing a brown discoloration and shrivelling.
Infections can occur on shoots, leaves, rachises and fruit. Infections generally occur during the early stages of shoot growth in early spring. During early spring rains, spores are released in large quantities from overwintering pycnidia on diseased canes and spurs. Spores are splashed by rain onto young, developing shoots and infection occurs when free moisture remains on the unprotected green tissue for many hours. Young, rapidly growing tissues are most susceptible. Shoot and leaf lesions appear within 3-4 weeks after infection, but do not form new spores until the following year. Rachises are susceptible until the fruit is larger than pea-size. Fruit infections occur primarily from bloom through shatter, then remain dormant until just before harvest.
Lesions on shoots, leaves, and rachises are the most common symptom of the disease, but a fruit rot can also occur.
Elongated black lesions develop along the basal part of shoots and lesions often split the green tissue. Numerous lesions give the surface a blackened, scabby appearance. When infections on shoots are numerous, they often run together and form dark blotches that crack. Shoot infections cause symptoms on the canes that are readily observed in the winter. In the dormant season, infected canes may appear bleached, and numerous black fruiting bodies (pycnidia) may develop along the cane’s basal region.
Leaf lesions often are numerous with brown or black-brown coloration and become covered with black, pimple-like fruiting bodies. These infections usually do not become visible until late summer. Severely infected leaves are misshapen with a crinkled appearance, yellow, and fall from the vine prematurely. Small leaf spots also can occur early in leaf development which can severely crinkle or misshape the leaf. Lesions can also develop on leaf petioles.
Rachis infections cause elongated black lesions like those on shoots. Rachises can become brittle if infections are high, causing portions of the cluster to break off before harvest. Lesions that girdle the rachis cause the fruit below to shrivel.
Infected fruit will turn brown, shrivel and eventually drop.
Overwintering lesions on canes and spurs are the primary source of inoculum for new infections. Remove infected canes and spurs during dormant pruning and destroy the wood by burning or burying.
Extensive build-up of the fungus on dead canes and spurs in the vine may require fungicide sprays to reduce disease problems. Cane and leaf infections can be prevented by one or two early-season sprays; the number of sprays depending on the extensiveness of previous year’s infections and occurence of prolonged rainy periods. The bloom through fruit set period, particularly if it is rainy, is the most critical time to protect fruit from infections. See the Fungicide Efficacy Table for comparisons of various labelled fungicides.
Pscheidt, J.W. 2002. Cane and Leaf Spot. Online Guide to Plant Disease Control. Oregon State University.
Phomopsis Cane and Leafspot. University of California IPM Pest Management Guidelines.
J. Travis, J. Rytter, and K. Hickey. 2003. Phomopsis Cane, Leaf Spot, and Fruit Rot. Penn State University.
Phomopsis Cane and Leaf Spot of Grape. Cornell Cooperative Extension.