Cherry Leaf Spot
The forecast model is based on the studies from Eisensmith and Jones 1981 on sour cherries (Montmorency variety). The EFI index (Environmental Favorability Index) is calculated on the basis of temperature and leaf wetness duration. No infections occurred below an EFI value of 14. However, below an EFI of 24, no infections occurred in about half of the cases investigated. The model thus shows too many supposed infections in the range between EFI 14 and EFI 24, which later lead to no symptoms. At the same time, the authors found indications in other experiments in 1982 that an interruption of leaf wetness leads to a reduction in the intensity of infection. For this reason, we have incorporated a factor which, when leaf wetness is interrupted and then restarted by dew, reduces the further course of infection (similar to primary infections with apple scab).
Eisensmith and Jones also found that there is a close correlation between the daily EFI index and the progression of symptoms (R2 = 0.73).
Eisensmith, S. P., and Jones, A. L. 1981. A model for detecting infec- tion periods of Coccomyces hiemalis on sour cherry. Phytopathology 71: 728-732.
Eisensmith, S. P., Jones, A. L., and Cress, C. E. 1982. Effects of interrupted wet periods on infection of sour cherry by Coccomyces hiemalis. Phytopathology 72:680-682.