It is most severe when a cool, rainy period of 4 - 5 days precedes several hot, sunny days. Although it appears NLB is not fungal caused, the disease is reduced when ziram is included in the cover sprays. Wet weather is ideal for most fungal diseases. If summer rains are a frequent event in your area of the state expect an increase in sooty blotch and flyspeck, black rot, bot rot, bitter rot and any other rots that might have made their way into your orchard. As always, good orchard sanitation is a must for control of summer rot disease problems.
Grapes are at bunch closing, a stage when berries within the cluster begin to touch.
This is an important time to apply a fungicide to protect against Botrytis bunch rot since it is the last opportunity to protect the interior of the berry cluster. Botrytis is particularly bad on tight-clustered French hybrids, such as Vignoles and Seyval, and most vinifera varieties, especially Pinot noir, Riesling, and Chardonnay. Rovral has been the standard fungicide for Botrytis control over the past few years, but a new product, Vangard, was registered this year. Recommendations from New York call for alternating Vangard with Rovral or tank mixing the two together. Sprays should be directed toward the cluster zone and applied in enough water to get thorough coverage.