Pathogens
Brown rot of stone fruits is caused by several species in genus Monilinia (Dowling et al. 2019). The three species responsible for the greatest losses worldwide include M. fructicola, M. fructigena, and M. laxa (De Miccolis Angelini et al. 2022). In eastern North America, M. fructicola predominates (Sinclair and Lyon 2005). While M. laxa also occurs in the U.S., M. fructigena does not and is considered a quarantine pathogen (CABI 2022).
Hosts
Brown rot can occur on a variety of rosaeceous trees and shrubs but is most common and destructive on Prunus (cherry, plum, apricot, nectarine and peach) (Sinclair and Lyon 2005).
Symptoms & Signs
Brown rot is a common disease in southern New England that affects blossoms, foliage, shoots, fruit and stems on susceptible trees. The fungus often becomes established on blossoms and succulent shoot tips soon after bud break and then lingers in the tree canopy all season long. Symptoms often include blighted flower buds, brown and undersized foliage, wilted shoot tips, and scattered twig and small branch dieback. Fruit can be infected at any time but susceptibility to infection increases as they approach maturity. Symptoms of fruit infection first appear as small, water-soaked lesions that rapidly expand to consume the entire fruit. Whenever environmental conditions are favorable (mild to warm, wet and humid), Monilinia produces large masses of spores that are splashed or blown onto nearby twigs and fruit, initiating new disease centers. Infected blossoms and fruit often have a very conspicuous, gray-brown, powdery coating of spores. This is a sign of the pathogen that can be used to identify the disease in the field. Stem cankers can cause localized or widespread canopy dieback and are accompanied by copious production of gum around the wound. All Prunus species produce amber-colored gum in response to injury (biotic or abiotic) on stems, branches and the main trunk, a process that is known as gummosis. The pathogen can overwinter within stem cankers, blighted leaves and fruit, especially fruit that has fallen around the base of the trees. Diseased and shriveled fruit may be held in the canopy (known as “mummies”), providing a large inoculum source to infect newly developing tissues the following season if they aren’t removed.
Management
Remove infected leaves, shoots and fruit to reduce inoculum within and around the tree. Prune branches to maintain an open canopy for better air circulation and sunlight penetration, which promotes foliage drying and limits conditions conducive for infection. If trees are subjected to extensive shade, especially during the first half of the day, the disease can be difficult to control once established. If spring conditions are particularly wet, then chemical management may be necessary to control brown rot. Begin applications just before buds open (when buds show a pink or white color). Fungicide applications should be made at regular intervals according to label recommendations. Fungicides labeled for use against Monilinia include: calcium polysulfide, copper hydroxide, copper salts of fatty and rosin acids, fenarimol, iprodione, mancozeb, propiconazole, sulfur, thiophanate-methyl and ziram. Many fungicides should not be used on fruit intended for human consumption, so carefully check the label prior to application.
Citations
CABI Compendium 2022. Monilinia fructigena (brown rot), https://doi.org/10.1079/cabicompendium.34747
De Miccolis Angelini RM, Lucia L, Celeste R, Stefania P, Francesco F, and Gianfranco R. 2022. Tracking of diversity and evolution in the brown rot fungi Monilinia fructicola, Monilinia fructigena, and Monilinia laxa. Frontiers in Microbiology 13, https://doi.org/10.3389/fmicb.2022.854852
Dowling M, Ritchie DF, and Schnabel G. 2019. Brown rot of stone fruits. The Plant Health Instructor 19, https://doi.org/10.1094/PHI-I-2000-1025-01
Sinclair WA and Lyon HH. 2005. Diseases of Trees and Shrubs, 2nd edn. Cornell University Press, Ithaca, NY.