In Missouri and much of the Midwest, grape growers have had the most rot pressure in the last 10 years. We have had rain every week and the challege of black rot on the grapes has been intense. Normally, we spray 7 days before bloom and 7 days after bloom. Studies have shown that this period is very important to eliminate rot pressure for the rest of the season. Thereafter, we spray on a two week interval. This year we have had to up the schedule to every 1.5 weeks. This interval plays havoc on my schedule since I generally tend the grapes on the weekends. I have had to go to the vineyard during the week and spray. In spite of all the spraying, we still got a little black rot! I am estimating a 2%-3% loss of crop due to black rot. Not a lot but still a little loss.
The good thing right now is that we are starting to accumulate sugars in the grapes. Grapes fend off black rot naturally once the grapes get to 6-8 brix. We are right there. So we are out of the rot woods.