Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/29/02
Contacts:
Mark Gleason, Plant Pathology, (515) 294-0579, mgleason@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning May 3, 2002
Managing Grape Anthracnose in Iowa
By Mark Gleason
Extension Plant Pathologist
and
Kiersten Wise
Plant Health and Protection Student
Iowa State University
Each spring, Iowa grape growers look at their vines in anticipation of the delicious fruits they will provide in the fall. Few realize that they are not the only ones waiting to reap the benefits of the grape vine.
Anthracnose, a fungal disease of grapes, has also been waiting patiently all winter to "spring" upon your grapes. So what is this disease and what can you do to avoid sharing your fruit with it?
Grape anthracnose (Elisinoe ampelina) is a fungus that produces structures called "sclerotia" that allow it to survive through the winter on infected canes or berries that have fallen on the ground. Each spring periods of rain "wake up" the fungus and it starts an infection cycle. Rain disperses the fungus to actively growing plant tissue, such as buds, where it will infect the plant.
How do you know if you have it? Look on shoots for gray or brown spots with dark edges. These spots are called lesions, and can merge and weaken the stem. Infected berries have dark spots with sunken white centers that resemble a "bulls-eye." Leaves will first show small, circular brown spots. Later in the season, the centers of these spots will turn a lighter shade of brown and drop out.
Fortunately, anthracnose is easy to prevent and control. Using good sanitation practices goes a long way in controlling an outbreak of the disease. Rake up dropped leaves and berries in the fall and prune out diseased canes. These actions will decrease the amount of fungus that over winters, reducing incidence of anthracnose in the spring.
Applying a lime sulfur spray at bud break (when you first see green emerging from the bud) in the spring will protect the grapes from the fungus. Timing of this spray is critical, because rainy periods will quickly move the fungus to the leaves if they have emerged from the bud. This spray is usually sufficient to ward off anthracnose for the entire season.
Lime sulfur is a certified organic spray, so there is no worrying about handling or consuming a pesticide, and it is suitable for use in sustainable or organic systems. Lime sulfur is relatively inexpensive, and can be found in many garden centers.
If left untreated, anthracnose can "girdle the vine" weakening it and decreasing the quality and quantity of the fruit yield. Anthracnose is particularly severe during wet, humid springs, so watch carefully for bud break during these conditions.
Common Iowa Grape Varieties
Growing varieties suited for Iowa will also help the plant resist diseases. Table grape varieties common in Iowa include:
Edelweiss
Swenson Red
Vanessa
Reliance
Buffalo
Price
Fedonia
Bath
Steuben.
This is only a partial list. Contact your Iowa State University Extension county office for varieties that will grow well in your area.
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