Brown Rot Blossom and Twig Blight

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

The fungus survives in mummies, twig cankers, and remaining diseased flower parts and spurs. Spore pads (sporodochia) on old infections also may provide inoculum for spring infection. Spores are airborne or rain splashed. Optimum conditions for infection and disease development are rainy weather during bloom with temperatures in the mid-70s (°F). All flower parts are susceptible to infection, and these infections may lead to blossom blight.

Unlike brown rot on peach and nectarine, control of spring brown rot of prune does not appear to have any effect on harvest levels of brown rot. However, in orchards with chronic blossom and twig blight, spring applications are recommended.

Good orchard sanitation helps reduce the amount of brown rot inoculum in spring. Have pruning crews remove all fruit mummies and blighted shoots. Remove the mummies from the orchard and destroy them. If left on the orchard floor, mummies will produce inoculum in the spring. You can cultivate the orchard floor to bury fruit mummies and reduce inoculum production. Dense ground cover maintained during bloom favors the production of inoculum by fruit mummies.

Treat at green bud and again at full bloom. An intermediate treatment at the popcorn stage may be necessary if bloom is prolonged and weather favors disease development. Fungicides are most effective when applied before a rainfall and allowed to dry.