Tree Diseases: Brown Rot Blossom Blight (Monilia fruiticola)
Brown rot blossom blight is a fungal disease that infects a bevy of stone fruit trees. The disease is caused by the pathogen Monilia fruiticola. Monilia fruitocola invades susceptible trees through various plant parts, including blossoms, branches, and shoots. Once the fungus becomes established within a tree, it induces a blossom blight, which causes the infected blossom to wilt. Infected fruit gradually decay, resulting in a significant reduction in fruit yield. Severely infected trees will exhibit extensive twig and branch dieback throughout the crown. Eventually, infected trees may succumb to infection.
Distribution & Habitat
Brown rot blossom blight is widespread throughout the United States. Infections may occur wherever susceptible trees are present.
Brown rot blossom blight infects stone fruit trees, including cherries, plums, and peaches. Ornamental flowering trees such as weeping cherry, and flowering plum trees may also be infected. Plum trees are less vulnerable to infection than peach and cherry trees.
The fungus overwinters on infected twigs, shoots, branches, and bark, as well as on diseased blossoms and mummified fruit that have remained attached to the tree. Fruit that has dropped to the ground may also harbor the fungus. In early spring, small fruiting structures called apothecium arise on infected plant material. These small fruiting structures resemble mushrooms, and become increasingly visible as they mature. Once temperatures exceed 40°F, and conditions become sufficiently moist, infectious spores called conidia are released from the apothecium, and dispersed by insects, splashes of rain, or air currents to nearby trees, where they initiate new infections.
Two to three weeks prior to ripening, the fruit produced by cherry, plum, and peach trees becomes highly susceptible to infection. As the harvesting period approaches, infections will often increase in frequency. The disease is especially problematic when rainfall is abundant. The fungus will invade vulnerable fruit through wounds they have sustained due to pruning or inclement weather. New infections can occur throughout the growing season. From late fall to early winter, as cooler temperatures prevail, the fungus enters dormancy, and overwinters in the diseased plant material. It resumes activity the following spring, beginning the cycle anew.
Symptoms of Infection
Disease symptoms appear in spring, shortly after bud expansion has begun. Diseased flowers will turn brown and wilt. As the infection advances, diseased petals will appear water-soaked, before collapsing inwards, and becoming laden with masses of spores. Infected flowers will often adhere to twigs into winter. Eventually, the infection will spread from the flowers into nearby twigs and small branches. During this period, extensive foliar dieback may occur. When branches are infected, a sticky or gummy substance will develop on the surface.
Once the infection reaches a twig or branch, it will often incite the formation of a canker. As the canker enlargens, it can girdle the infected portion of the tree. Infected fruit will form small, tan colored lesions that increase in size. When conditions are humid, the lesions will produce grayish brown spores on the surface of the fruit. Diseased fruit will shrivel, and cling to the branch. Peaches may form rings of gray sporulation as the infection deepens.
- Repeated applications of nitrogen-based fertilizer can exacerbate infections, and are not recommended for use around diseased plants.
- Fruit that fails to ripen or is insufficiently pollinated will often be cast from the tree, and plummet to the ground. If not collected and disposed of, cast fruit can increase the amount of inoculum present.
- Remove and dispose of infected twigs, branches, and fruit. Prune periodically to improve air circulation throughout the crown, and promote a rapid drying of damp foliage. Avoid wounding healthy fruit when pruning, as this can create potential openings for infection. Use a solution composed of nine parts water and one part bleach to sanitize pruning equipment prior to performing each cut. Dry disinfected tools thereafter.
- Provide control for insects that damage fruit.
- Trees may be sprayed with registered fungicides to reduce the incidence of infection. Apply fungicides during the bloom period to control the blossom blight phase. Multiple applications may be required to suppress the disease.
- When applying fertilizer, use low to moderate amounts of nitrogen.
Photo courtesy of Michigan State University