Apricot: Brown Rot

Problem
The blossoms and young leaves wilt, decay, and turn brown during the first 2 weeks of the bloom period. Often the decayed blossoms and leaves fail to drop, and may hang on the tree throughout the growing season. In humid conditions, masses of gray spores may appear on the infected flower parts. There is often extensive twig dieback. Sunken lesions (cankers) may develop on the twigs and branches as the season progresses; a thick gummy material often oozes from these cankers.

Analysis
This plant disease, caused by either of 2 closely related fungi (Monolinia laxa or M. fructicola), is very destructive to apricots and to all of the other stone fruits. The fungi spend the winter in twig cankers or in rotted apricots (mummies) in the tree or on the ground. In the spring, spores are blown or splashed from cankers or mummies to the 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 sometimes oozes from the cankers, and tufts of gray spores may form on the infected areas. Spores from cankers and infected blossoms or mummies are splashed and blown to the maturing fruit. Young apricots are fairly resistant to infection, but maturing apricots are vulnerable. Brown rot develops most rapidly in mild, moist conditions.

Solution
If there are still uninfected blossoms left on your tree, spray with a fungicide containing captan, triforine, or chlorothalonil to protect them from further infection. Repeat the spray 10 days later. Next spring, spray trees when first flowers begin to open and continue to spray according to label directions. To protect maturing apricots from infection, spray them with a fungicide containing captan or triforine about 3 weeks before they are to be harvested. Remove and destroy all infected apricots and mummies. Prune out cankers and blighted twigs. Clean up and destroy all debris around the tree. Plant resistant varieties.