This fungal disease causes an easily distinguishable fluffy brown rot of the fruit of peach, nectarine, plum, prune, sweet and sour cherry, apricot, almond, Japanese quince, and the ornamental stone fruits. The disease is most severe in areas with frequent spring and summer rains, so conditions have favored the development of the fungal pathogen this year.
Brown rot is caused by Monilinia fruticola or M. laxa. These fungi may infect blossoms, fruits, twigs, and small branches. In warm, damp conditions, the fruit quickly turns light brown, followed by development of tan-to-gray spore tufts that give a fuzzy appearance. The rotted fruit eventually shrinks and blackens, taking on a mummified look. These mummies may stay attached to the tree, serving as an overwintering site for the fungus.
Brown rot is not known to cause leaf infection. Besides fruit rot, however, it may infect flowers, resulting in wilting and the production of the same spore tufts seen on the fruit. If the fungus invades stems, cankers result. Often the cankers ooze gum or sap. Injuries and insect activity may also cause gum or sap production on many stone fruit trees.
The most significant disease control measure is reduction of inoculum. Remove mummified fruit and prune out infected twigs or cankers. The fungus will continue to develop on unpicked fruit throughout the season, so remove affected fruit as it appears. Also remove all fallen ripe fruit during the season--don't wait until autumn. Insect control will also help manage this disease.
Commercial fruit growers generally use fungicides during bloom and again three weeks before harvest to help control brown rot. For next year's reference, the bloom sprays should be applied when blossoms first appear and again four or five days later at full bloom. Some control can be attained yet this year by spraying two to three weeks before harvest and repeating at seven- to ten-day intervals. Many fungicides will work, but captan is probably the easiest to obtain and the least expensive for homeowners. Read the label carefully to honor preharvest intervals (number of days before harvest that you can spray a particular chemical). Brown rot is discussed in detail in Report on Plant Diseases No. 804.