Answer: This is a fungal infection and the basic controls are sanitation and possibly a spray program. The fungus will overwinter on old grapes and vines, so these should be cleaned up thoroughly in the fall. Prunings should also be removed and destroyed. Infected leaves should be picked off to try to limit the spread of the infection early on as well. Picking the grapes as soon as they are ripe will limit insect feeding damage (such as by wasps) and transmission that way. Finally, avoid wetting the leaves if you water and try to maintain good air circulation around the vines; good pruning can help with this. You may also want to consult with your county extension (746-3700) about the best spray regime for your planting. This would be determined each year based on the weather and on the susceptibilities of the varieties you are growing.
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