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Brown rot

Monilinia fructicola (G. Wint.) Honey
Monilinia laxa (Aderhold & Ruhland) Honey

Infected flowers turn brown, wither, and either become fixed to twigs as a gummy mass or drop like unpollinated flowers (A). Apricot is the most susceptible to blossom blight, followed by prune, sweet cherry, peach, sour cherry, and then plum. If infected blossoms do not drop off, the fungus may grow through the flower stem and into the twig below. Twigs develop elliptical to fusoid cankers with profuse gumming at the margin between diseased and healthy tissue (B). Leaves on infected shoots turn brown and wither, but remain attached. In some instances, twigs are girdled and killed.

On the fruit, infection first appears as soft brown spots. These rapidly expand and become covered with powdery masses of tan spores (C). Infections spread rapidly from fruit to fruit when they are touching one another. Rotted fruits typically shrink into a wrinkled "mummy" as they dry on the tree (D). Both immature and mature fruit infected with brown rot tend to remain on the tree and form mummies (E). Mummies that fall to the ground may produce a spore-bearing mushroom-like structure called an apothecia the following spring (F); its importance in the disease cycle is minimal in the Northeast and mid-Atlantic region.

Distribution

Widespread; common to all fruit-growing regions in eastern North America.

Similar Species

Blossom blight can be confused with blossom blast caused by Pseudomonas syringae van Hall; fruit rot can be confused with Alternaria fruit rot and Rhizopus rot. The presence of fungal sporulation helps to differentiate the different diseases. Brown rot-infected fruit will produce powdery gray to light brown spores, whereas Alternaria-rotted fruit will develop a dark green to brown mass of spores. Rhizopus-infected fruit develop a softer rot than brown rot-infected fruit. Also, Rhizopus produces "whisker-like" tufts of grayish-white sporangiophores capped with a black spore mass at their tips; the sporangiophores can exceed 1 cm in length.

Management

Prune out mummified fruit and cankers during the dormant season and burn or bury them deep in the soil. Remove wild or neglected stone fruit trees in the area that may serve as reservoirs for disease. Fungicides should be applied during bloom if warm (> 18°C) rains are predicted, especially in orchards where inoculum levels are high. Fruit are very susceptible to infection 1–3 weeks after shuck split and again from 3 weeks prior to harvest through the harvest period. Fungicides are often used during these periods to protect fruit.

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