What’s wrong with my grapes?
Question:
My somerset seedless vine (about five years old) now has berries and they are getting some fatal disease. They start with a brown spot, then it progresses to a brown bullseye, then half the berry shrivels, then the whole thing is mummified. I suspect this is black rot, yet again, even after cutting back all but one vine to the left, and one to the right (despite removing mulch, removing neighboring bushes, etc., no watering, etc.). It seems this disease will stay with this plant year to year. Is this true? Does this disease become permanent (and will it spread to two nearby vines (different cultivars)? This seems like a permanent condition now (three years in a row despite measures). We do not want to use commercial antifungal chemicals in our garden.
Answer:
Marjorie Peronto, Extension Educator
Our Plant Pathologist has identified this as the fungal disease black rot of grape. It is the most common and serious disease of grapes in Maine, and during years when the weather is favorable losses can range up to 80% of the crop. Non-chemical methods for managing this disease are as follows:
- Fall clean up may be the most important component of a control strategy because this can remove most of the inoculum (spores) source from the planting. Rake up all leaves and fallen mummies. Be especially careful to remove mummies that remain attached to the vine and, when pruning, preferentially prune out infected canes and be careful to remove infected tendrils.
- Plant in locations that will provide plenty of sun and air circulation, and orient rows parallel to the prevailing winds (generally west-east). Provide for proper vine spacing when planting, try to maintain an open canopy, and maintain good weed control. These practices will allow for rapid drying of the plants.
- Select resistant varieties when planting.
If you decide to resort to a fungicide, please see our fact sheet on Black Rot of Grape for recommendations.