Make observations at five or six locations in each field. Examine leaves on 20 to 25 stems and average these observations to determine the disease level in the field. The thresholds were developed by Dr. Hershman at the University of Kentucky, and have been modified slightly to fit Pennsylvania conditions. The thresholds should be used with other information. For example, if a threshold is reached for powdery mildew and an extended period of hot, dry weather is predicted, spraying may not be needed.
Weather always can intervene and reduce or increase a disease situation.
Step 7 Understand risks. One of the problems of using a foliar fungicide is the inability to determine if disease-favorable conditions will persist after a fungicide has been applied. Fungicides are valuable only if yield and quality are threatened by disease. Similarly, fungicides will be of limited value if other diseases such as take-all, loose smut, and head scab, which are not controlled by foliar fungicides, develop. Also, fungicides may be of limited value if yield and quality are reduced by nondisease factors such as lodging, delayed harvest, and short grain fill period.