The photomicrograph below illustrates a stained thin section of peach fruit infected with Peach Brown Rot, a serious disease of fruit trees caused by the fungus Monilinia fructicola. Also affected by this devastating fungus are other stone fruits such as cherries, plums, prunes, nectarines, and apricots.

The fungus forms cankers on the twigs of the fruit trees, but it does the most damage when it rots blossoms and fruit. At harvest, apparently healthy fruit may be contaminated with spores and decay during storage and marketing.

M. fructicola has two spore types. The ascospores, which are produced sexually, are stored over the winter in mummified (rotted and dried) fruits and in twig and branch cankers. They are released in the spring and carried by the wind to unopened blossoms and young shoots. If conditions are warm and wet, the spores will germinate. The summer spores, conidia, are produced vegetatively (self-cloning) and are carried by the wind and insects to other parts of the tree where they can infect the maturing fruit.