Again this year our grape vines are having problems. In the late spring we see formation of grape clusters but as spring goes into summer the little grapes in the cluster start disappearing. Does anyone have the answer to this problem?
I found this at the north Dakota extention website
Q: I have had grapevines for about 10 years. Until two years ago, they produced good crops. In recent years, I get adequate vine growth and many florets that begin to develop into grape clusters. However, when the grapes get to 1/8 inch in diameter, the grapes turn hard, black and do not develop into edible grapes. Last year, the vines produced minimal edible grapes. I added superphosphate to the root system, but it did not help. (e-mail reference)
A: It could be fruit rot or botrytis bunch rot. An on-site collection of the grapes and perhaps a lab culture will be needed to make a positive identification. Without knowing the pathogen, I would suggest starting a spray program using a bordeaux mixture as the plants begin to show new growth. Spray again on a two-week basis. I would encourage you to get an application on the grape clusters before they close to be sure the fungicide hits all sides of the individual grapes. This is a generic recommendation that should provide some protection. It’s like a doctor telling you to take “two aspirins,” hoping it will take care of the problem.
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