Brown Rot Blossom and Twig Blight

Blossom and twig blight causes the collapse of young blossom spurs and associated leaves. A gummy exudate is present at the base of flowers. Gray-brown spore masses form on diseased flowers under high humidity.

Monilinia spp. survive on diseased twigs and mummified fruit. Its development is favored by moderate temperatures and moist-to-wet conditions during bloom or on mature fruit. The disease is not common on most plum cultivars because unlike peach and nectarine, many plums are less susceptible to brown rot blossom and twig blight, as well as fruit rot. For late-season cultivars, if an orchard has a history of the disease, or if rainfall occurs before harvest on mature fruit, protective fungicide treatments may be necessary to prevent brown rot of fruit. Late-season cultivars with harvest dates in August or September include Angeleno, Autumn Beaut, Betty Ann, Casselman, Howard Sun, and Rosemary.

Sanitation includes removal and destruction of mummified fruit from trees and orchard floors after harvest and before bloom, as well as heavily thinned fruit from orchard floors that may be colonized by the pathogen and function as a source of inoculum during fruit maturation. On susceptible cultivars, apply a protective fungicide treatment as a delayed bloom application (20-40% full bloom). A second application may be necessary during protracted flowering or during foggy or rainy weather. Protective fungicide treatments to prevent fruit brown rot are usually not needed on early or mid-season varieties. As discussed above for late-season cultivars, if an orchard has a history of the disease, or if rainfall is forecasted on mature fruit in the harvest period, protective fungicide treatments may be necessary to prevent brown rot of fruit.