General Information. Brown rot affects all stone fruits, including those grown for ornamental purposes. The blossom blight phase of the disease is rare in the arid fruit production regions of eastern Washington. The disease can destroy blossoms, fruit, and stems. Greatest losses are from blossom blight and destruction of fruit in the orchard, in transit, and in storage. The disease can develop rapidly, and a few infected fruits in storage can lead to destruction of all surrounding fruit. Blossom blight may lead to twig infections which are potential sources of infection for the developing fruit, and sometimes a serious problem in fruit production. Brown rot in eastern Washington is caused by Monilinia fructicola. The fungus is common throughout the United States. Brown rot is most serious on peaches, plums, and cherries, but also affects apricots. Although apples and pears have also been reported susceptible to brown rot, the disease is of minor importance on these crops in Washington.

Symptoms. Brown rot of blossoms appears as a sudden wilting and browning of the flower parts. If conditions are moist, the dead flowers are soon covered by a grayish brown powder consisting of masses of fungus spores. These are the major source of infection of fruits. The disease first appears on the fruit as a small, circular brown spot that rapidly increases in size and develops into a soft rot. Eventually tufts of gray-brown spore masses appear on the affected area and soon cover the diseased fruit. Diseased fruits often hang on the tree long after being completely rotted. The fruit dries into a firm mummy. The fungus may spread into twigs from both infected blossoms and fruit. On twigs and smaller branches, brown rot cankers are oval, definite in outline, brown in color, and usually sunken. The twig is sometimes girdled and dies.

Epidemiology and Forecasting.The fungus lives over the winter in infected twigs and fruiting spurs and in mummified fruit on the tree or on the ground. Masses of spores are produced on these infected tissues in the spring and cause blossom blight. Cup-shaped fruiting structures on long stalks are also sometimes formed on overwintering mummies. The inner surface of these cups bears many spore-containing sacs. These spores land on blossoms and give rise to the blossom blight and possibly also cause twig infections. As with many diseases, cool, wet weather favors the development and spread of the fungus.

Management. Control of brown rot involves three approaches: sanitation to reduce or eliminate sources of infection, providing an orchard environment less conducive to disease development, and the application of fungicides. Removal of mummified fruits is probably not feasible in most commercial orchards. Cultivation around trees will bury many mummies. In some situations, it is feasible for home gardeners to remove the mummified fruit in the tree and rake up and destroy infected fruit on the ground. In addition, pruning out infected twigs can help to eliminate sources of spores. This pruning should take place in the late spring or early summer when they are readily visible. The brown, dead leaves attached to these girdled twigs, or the dead, brown blossoms at this time of year, make these infections quite obvious. If pruning is delayed until the dormant season, locating infected twigs is almost impossible. Spring or early summer pruning will also reduce the number of spores responsible for fruit infection. Improving air circulation through trees will do much to eliminate the moist conditions favorable to brown rot. Remove trees and brush surrounding the orchard. Avoid planting trees too close and remove some trees where they are crowded. Pruning to provide more open crowns will permit better air circulation within the individual tree and will also provide better spray coverage. Infected spurs and shoots should be removed as soon as they are noticed. In western Washington, or during wet springs in eastern Washington, preventative fungicide applications are necessary in the spring to protect blossoms from infection. Several fungicides are registered (see EB0419, EB0918). An application should be made at early bloom (popcorn) with two additional sprays at 7-10 day intervals during the bloom period. To prevent bee kill, do not mix an insecticide in with these fungicides. Fungicide sprays prior to harvest are necessary during wet weather to control fruit rot on cherries, peaches, apricots, and nectarines. Be sure to read and follow label directions, especially regarding the interval between the last application and harvest. Bruising of fruit during harvest should be avoided, and the fruit should be kept cool until it reaches market.

Back to top

Online References
Biggs, A.R., Hickey, K.D., and Yoder, K.S. 1997. Brown Rot. West Viriginia University Kearneysville Web Site

Teviotdale,B.L., and Gubler, W.D. 1995. Brown Rot. UC Pest Management Guidelines, University of California Statewide Integrated Pest Management Project Web Site

Back to top