We have received several plum samples with brown rot caused by the fungus, Monilinia fruticola. Brown rot can affect peaches, cherries, plums, apricots, and almonds. This is the time of year where sanitation becomes very important to control this disease next year.
Brown rot may affect the blossoms, fruit spurs, twigs, small branches, and fruit. One to several small, round, light brown spots form on a fruit as it ripens. In warm, moist weather the rot spreads very rapidly. The entire fruit may become semi-watery, decayed, and light brown. Tannish gray spore tufts break through the fruit skin, giving it a powdery appearance. Infected fruit continue to rot after harvest, turning into black shriveled "mummies", some of which remain on the tree over winter. Blossoms suddenly wilt, turn brown, and wither, and later they are covered with a tan-gray mold. Oval or elliptical, brown, sunken cankers form on the fruit spurs, twigs, and small branches. Gum commonly oozes out from the canker margins during wet periods.
Sanitation is critical for disease control. All dropped and rotted fruit should be promptly picked up and destroyed. Remove all mummies from trees. Prune out all cankers and blighted twigs after the last picking and during the dormant season. Prune trees annually to open the center. Remove and burn or bury all wild and neglected stone fruit trees. Follow a routine spray program for stone fruits. Fungicide sprays must be every 7-10 days from 2 weeks pre-bloom through harvest if wet weather persists.
For homeowners, products such as Daconil 2787 or Home Orchard Spray are available. Read the label for diseases controlled, timing of applications, and rates.
This article originally appeared in the September 15, 1995 issue, p. 133.