The anthracnose fungus, Elsinoe ampelina, overwinters in infected plant material. In the spring, when temperatures are 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. Anthracnose is a common grape disease in Iowa.
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.
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
Management consists of the following:
- Prune and destroy diseased plant material while plants are dormant to reduce the potential for disease the following year. Be sure to eliminate black rot mummies.
- Remove wild grapes around the area because these grapes can harbor disease organisms.
- Avoid planting grape plants that are susceptible to anthracnose.
- Promote canopy drying by pruning, training, row orientation, and proper spacing.
If your planting has had problems with anthracnose in the past, a delayed dormant spray (just before the buds break) of liquid lime sulfur will help to reduce the threat for the upcoming season. In addition, you may wish to consider a program of preventive fungicide sprays (mancozeb or captan) at 2-week intervals from bud break until the fruit begin to turn color. Prune out damaged shoots and clusters and remove the prunings from the vineyard, and rake the ground under the plants in fall in order to remove all fallen berries.
Photo credits: 1: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org; 2: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
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