VIEW ARTICLE

Ecology and Epidemiology

A Model for Detecting Infection Periods of Coccomyces hiemalis on Sour Cherry. S. P. Eisensmith, Graduate research assistant, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824; A. L. Jones, professor, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. Phytopathology 71:728-732. Accepted for publication 29 December 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-71-728.

A regression model relating hours of continuous moist chamber exposure and temperature to infection of sour cherry by conidia of Coccomyces heimalis, cherry leaf spot fungus, was developed from published data. The model is EFI = [–11.0 + 0.2858W + 1.4639T –0.0019W² – 0.0389T² – 0.003 WT]², in which T = temperature (C), W = hours of leaf wetness, and EFI = environmental favorability index from 0 to 100. An EFI of 14 was selected to delineate the minimum conditions for infection under field conditions. EFI was ≥14 in 62 of 65 validations for which infection was detected by observing marked shoots of orchard trees every 4–7 days, and <14 in 15 of 18 validations for which no infection occurred. In 34 of 35 cases in which infection was detected by exposing potted trees during putative infection-favoring weather, EFI was ≥l4; and in 20 of 39 cases in which no infection occurred, the EFI was <24. The infection model is useful between 8 and 28 C, and for leaf wetness periods up to 70 hr. Daily EFI values were linearly related to rates of disease increase in Michigan in 1978 and 1979.