These two diseases often occur together because they have similar and numerous wild hosts.
Sooty blotch and fly speck are most likely to develop when temperatures are 65-80°F and when humidity is high. This combination occurs most frequently when nighttime temperatures remain above 65°-70°F during summer, or during extended warm, rainy periods. Sooty blotch and fly speck infections not visible at harvest can develop in storage.
Plant disease-resistant varieties. Spray with a copper soap fungicide when disease first appears, and repeat at 7- to 10-day intervals for as long as needed. For optimum control, begin spraying 2 weeks before disease normally appears, or when temperature and humidity conditions favor disease establishment. If summer diseases such as sooty blotch and fly speck have been a serious problem in past years, dormant sprays of a copper soap fungicide, applied in early spring, may help eradicate overwintering infections that became established on twigs the previous season. We recommend Soap-Shield® Flowable Liquid Copper Fungicide*.
*NOTE: If used frequently, Soap-Shield may cause leaf burn. If leaf burn develops, discontinue the use of Soap-Shield spray.