Grape black rot must be stopped before it starts

Q. The leaves on my grapes and my grape clusters have dots on them. Is this going to harm my crop this year?

Samantha from Youngstown

A. Yes, it will harm your crop. This disease will turn your grapes into mummified raisins before they are ready to harvest.

It is called grape black rot. It is the most common disease of grapes in our area. You will notice lesions on grape leaves which look like dark brown spots. If you look closely, you will see tiny black dots (spores) on the leaf. The dots are the fruiting bodies of this disease.

We are far from the time to be able to control this disease with any kind of spray. That is only in spring just before bloom. But there are other control options and cultural practices we can use now to slow the disease some, but mostly reduce it for the next growing season.

First, ask yourself what kind of trellis you are using to support your vines. If there are vines growing over your head, this is not a good practice for a healthy grape crop. It is the wrong environment for grapes. The trellis should be poles and a wire or two, about 5- to 6-foot off the ground. Sunlight is ultimately important — no shade. Grapes should be pruned and trained to grow on this type of trellis for health and productivity.

Right now, you can increase the air circulation and sunlight penetration by doing some selective pruning. This will help the leaves dry off during this moist, humid time of year. Also, remove any significant signs of the disease (without removing everything). As for preparations for next year, remove all of the leaves and debris from the plant at the end of the season. Clean up the area to prevent the chance the disease will survive on the debris during the winter. Sanitation is most critical.

Resources for your home vineyard: GRAPE BLACK ROT:; PRUNING GRAPES:

Eric Barrett is OSU Ext. educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 from 9 a.m. to noon Mondays and Thursdays to submit your questions.

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