Pray for no rain!!! Do you have a plastic dome?
I have never sprayed anything on my Lapins.. I don't even spray for Plum Curculio (they hit sweet cherries, just not as bad as plums). Its right next to the house, everyone walks right where its growing...so i just leave it. The one year i had the best harvest, was the year we had no rain around ripening time. Rot seems to hold off until they turn darker red...and then it spreads like wildfire any time we get moisture. What i did do last year is i took small sheets of plastic and wrapped a few long branches that held a lot of fruit...that did work...the fruit didn't cook either, although i did worry about that so i left somewhat of a gap.