Problem: Brown Rot (Plum)
This plant disease, caused by either of two closely related fungi (Monilinia laxa or M. fructicola), is very destructive to all of the stone fruits. The fungi spend the winter in twig cankers or in rotted fruit, called mummies, in the tree or on the ground. In the spring, spores are blown or splashed from cankers or mummies to healthy flower buds. After penetrating and decaying the flowers, the fungus grows down into the twigs, producing brown, sunken cankers. During moist weather a thick, gummy sap oozes from the lesions, and tufts of gray spores may form on the infected areas. Spores from cankers and infected blossoms or mummies are splashed and blown to maturing fruit. Young fruit is fairly resistant to infection, but maturing fruit is vulnerable. Brown rot develops most rapidly in mild, moist conditions.
Apply a fungicide labeled for this disease, following label directions. Remove and destroy all infected fruit and mummies. Prune out cankers and blighted twigs. Clean up and destroy all debris around the tree.