Brown rot is a fungal disease of stone fruit caused by Monilinia laxa. It may cause serious damage to fruit during wet seasons. Early infections appear as blossom blight or shoot dieback. Later infections appear as a rot of ripening fruit on the tree and in storage.
Plant Parts: Leaves, shoots, buds and fruit.
Season: Spring - Autumn
Blossom Blight: Infected blossoms wilt, shrivel and become covered with greyish mold. Petals may appear light brown or water-soaked, similar to frost injury. Blighted blossoms do not produce fruit.
The amount of blossom blight directly affects the amount of fruit rot. Dead blossoms may stick to spurs and twigs until harvest, providing a source of spores for the fruit rot phase.
Twig Blight and Canker: On peaches and apricots, the infection may spread to twigs, causing brownish, oval cankers that may girdle and kill twigs. Gumming may also occur on infected twigs.
Fruit Rot: Fruit rot first appears as small, circular brown spots that increase rapidly in size causing the entire fruit to rot. Greyish spores appear in tufts on rotted areas. Infected fruit eventually turn into shrivelled, black mummies that may drop or remain attached to the tree through the winter. Brown rot can be serious on injured fruit such as nectarines split by rain.
Brown rot can spread after harvest and has the potential to cause severe post-harvest losses. Mature fruit can decay within 48 hours under warm conditions.
Prevention: Avoid overhead watering, since the spores travel by rainfall and splashing water. Keep weeds, cuttings and plant debris cleaned up and dispose of this material away from the tree to keep from spreading spores accidentally. Check out the Care instructions in the annual winter pruning section. Applying a copper spray at bud swell and repeating if necessary is a great preventative.
References: NSW Department of Primary Industries, Image: Whitney Cranshaw, Colorado State University, Alabama A&M and Auburn University, Bugwood.org, Gardening Knowhow, BC Tree Fruits, and the FST team.
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