PPDL Picture of the Week for
August 24, 2015
Grape Anthracnose (Elsinöe ampelina)
Bruce Bordelon, Professor, Department of Horticulture and Landscape Architecture
With all the rain we’ve had in 2015 it is not surprising to see more disease problems than normal. One disease that is widespread this year is grape anthracnose, aka black spot or Bird’s eye rot. There have been numerous reports from both commercial vineyards and home grape plantings. This disease is not uncommon, but is seldom widespread except in very wet years. All the rain we’ve had this year is making the disease worse than normal. In addition, the newer cold hardy grape cultivars from Minnesota appear to be highly susceptible to anthracnose. There are now several acres of Frontenac, Marquette and La Crescent planted in the state.
Anthracnose can infect all green grape tissues. Symptoms first appear early in the year on the first few internodes of new shoots. They are deep lesions with dark margins and a gray center (Picture 1). If the disease spreads to young tissue, it can distort and kill the shoot tips, giving the shoots a burned appearance (Picture 2) Leaf lesions often cause the leaf to distort and curl. Centers of the spots often fall out, leaving a shot-hole appearance (Picture 3). The disease spreads to developing berries. Berry lesions appear as a dark spot with a gray center, giving the disease its common name, Bird’s eye rot (Picture 4). Bird’s eye rot is mostly cosmetic, as it does not affect the eating or processing quality of the fruit. Severe infection, however, can reduce vine vigor and yield.
Managing anthracnose can be relatively easy. The best control method is to apply a delayed-dormant application of liquid lime sulfur or Sulforix (calcium polysulfide). This fungicide effectively kills the developing spores (primary inoculum) at the beginning of the season and prevents the disease from becoming established. If this spray is missed and the disease becomes established, control is more difficult. Lime sulfur will burn tender foliage so it must be applied just as buds are swelling, but before the leaves are exposed. After bud break mancozeb, captan and the strobilurin fungicides such as Abound or Sovran can provide some control and keep the disease from spreading. But the single application of lime sulfur usually provides nearly complete control. That’s why it’s important for growers with a significant problem this season to plan ahead for an early season fungicide application next year.