Black Rot Disease in Apples
Mirjana Bulatovic-Danilovich, WVU Extension Specialist, Consumer Horticulture –
Agriculture & Natural Resources
Black rot disease, caused by the fungus Botryosphaeria obtusa (Schwein), is concerning to homeowners with apple trees as part of their landscapes. All apple cultivars are susceptible to it, but it appears that McIntosh, Cortland, Empire and Northern Spy varieties are the preferred hosts. It seems that black rot is becoming more of a problem than usual. Normally, protectant apple scab programs would keep black rot in check. But, since incorporating other materials (like sterol inhibitors) that have no effect on these fungi, symptoms were more readily observed in the orchards throughout the state.
Symptoms on the fruit appear at the calyx end as brown/rotted lesions. As the lesions enlarge, they form a number of concentric rings (Figure 3).
season. Conidia are produced during the wet periods and are spread by rain, wind and insects. The peak spore discharge is during the four to six week period post petal fall. This disease prefers relatively high temperatures. The temperature has to be above 48 degrees Fahrenheit. Optimum temperature is about 78 to 80 degrees Fahrenheit and requires only four hours of wetting for leaf infection to occur. It takes nine hours of wetting at temperatures between 68 and 75 degrees Fahrenheit to have fruit infection. Spores infect leaves, flowers, wounds on branches, the calyx end of fruits and trunks. Under heavy disease pressure, leaves may drop prematurely, predisposing trees to winter injury.
will provide black rot control as well.