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Grape Anthracnose and Black Rot
This article was published originally on 7/25/2003
Anthracnose and black rot are two common Iowa grape diseases. They both like the same environmental conditions, so often one plant will have both diseases, which can lead to confusion.
The anthracnose fungus, Elsinoe ampelina, overwinters in infected plant material. In the spring when the temperature is at least 36 F, spores are spread by wind and splashing rain and can infect all aboveground parts of the plant. However, warmer conditions (up to 90 F) promote more severe infections.
Small, round, reddish spots begin to form on leaves as symptoms begin. On stems and fruit, spots develop into sunken, gray areas with dark reddish to purple edges. Spots can run together and kill entire shoots or berries. As spots develop on leaves, they form gray centers with dark edges that are typically angular rather than circular.
Black rot, caused by the fungus Guignardia bidwellii, can cause heavy losses to infected grapes, especially during warm, humid weather. Black rot starts as tiny yellow spots that grow to about 1/4 inch on the leaves. The centers of the spots turn rusty red. Tiny black dots usually form in the center of the spots. These dots contain thousands of spores that can produce new infections. Symptoms on fruit become apparent when the berries are about half grown. Infected berries can rot in a few days. They shrivel and become hard, black mummies, which contain the same tiny spore containing structures as leaf spots.
The primary winter survival mode for the fungus is in mummified berries. However, other infected plant material can be a safe haven for the fungus.
Management of these grape diseases consists of the following:
See the Midwest Commercial Small Fruit and Grape Spray Guide for fungicide scheduling.
For more information see the references below.
Year of Publication:
IC-489(19) -- July 25, 2003