Plant Disease Clinic--Highlights

Brown Rot

Cherry samples showing signs of brown rot have been arriving at the Plant Disease Clinic. Brown rot is caused by the fungus Monilinia fructicola and affects stone fruits such as peach, nectarine, apricot, plum, and cherry. The fungus may infect blossoms, fruit spurs, twigs, small branches, and fruit. Disease development is favored by warm, wet, humid weather.

Small brown spots appear on fruit as it ripens. In warm, moist weather the rot spread rapidly. The entire fruit may become watery, decayed, and light brown. Tannish gray spore tufts break through the fruit skin, giving it a powdery appearance. The rotted fruit eventually shrinks and turns black. These "mummies" may remain on the tree or fall to the ground.

Infected blossoms suddenly wilt, turn brown, and wither. Later they are covered with a tan-gray mold. Oval, 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 removed and destroyed. Remove all mummies from the tree. Prune out all cankers and blighted twigs after the last picking and during the dormant season. Prune trees annually to open the center and improve air flow. Remove and burn or bury all wild and neglected stone fruit trees. Wounded fruit are infected more readily than nonwounded fruit so handle fruit carefully to avoid scratches, punctures, and bruises. Fungicide sprays are effective for controlling brown rot. Products such as Funginex and Home Orchard Spray are available to homeowners. Thorough coverage is essential. Follow label directions regarding timing of sprays and rates.

This article originally appeared in the June 30, 1993 issue, p. 108.


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