Brown rot is common in fruit trees, caused by the fungus Monilinia fructicola. It can cause major fruit-crop losses in apricot trees, infecting the blossoms, fruit, spurs and branches. The fungus can spread via insects, wind and rain, or contact with diseased fruits. Preventing brown rot in apricot trees involves an aggressive disease management process and special care during the apricot harvest season.
Diagnose brown rot in your apricot trees. Look for the blossoms on your apricot tree to wilt and turn brown in the spring, staying attached to the tree into the summer. You'll also see brownish-gray spores covering the wilted blooms. Watch for rapidly expanding soft brown spots on the apricot fruits, followed by the fruit rotting, dying and shriveling. If the disease has moved beyond the fruits and into the spurs, it will cause infected canker to develop on the twigs and even the branches.
Remove all mummified fruit and cankers during the dormant season, either burning them or burying them deeply into the ground. Remove and destroy all rotted, dropped and overripe fruit from the apricot tree, the ground and storage sheds. Brown rot disease overwinters in mummies (dried infected fruit) and in infected twig or branch cankers, producing spores that will infect the spring blossoms and young fruit.
Thin your apricots early. Try to thin out your fruits before pit hardening. Apricots thinned after pit hardening are more susceptible to becoming infected on the ground after dropping than while they're still young and on the tree.
Prevent damage to your apricot fruits by insects. Wounds in the apricots allow the brown rot disease entry into the fruit to infect the tree. Use an appropriate insecticide to control fruit-feeding insects, such as the tarnished plant bug and the oriental fruit moth, so they don't create holes or other wounds in your fruits.
Handle the apricots carefully during harvest to avoid bruising or puncturing the fruits. Refrigerate the apricots at 32 degrees Fahrenheit immediately after harvest to slow the spread of the disease in the fruits.
Apply a commercially made protective fungicide spray to your apricot trees at least once each year during the dormant season, following the label's instructions. Apply a second spray at full bloom or when the petals begin to fall if you're experiencing warm, wet conditions during that time.