If this is the first year for those plums sometimes that happens. be sure to use dormant oil in late fall and again in early spring just as the snow is melting follow the directions and spray the whole tree according to schedule up to bud stage....one the bud is open we just spray the trunks up to under the first branch. Wear old long clothing, goggles, mask, hat & gloves, keep children & pets away until it dries, don't spray on days that it's going to rain and don't spray in the wind.
