A Model for Detecting Infection Periods ofCoccomyces hiemalison Sour Cherry

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Abstract
A regression model relating hours of continuous moist chamber exposure and temperature to infection of sour cherry by conidia of C. 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 0-100. An EFI of 14 was selected to delineate the minimum conditions for infection under field conditions. EFI was .gtoreq. 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 .gtoreq. 14; and in 20 of 39 cases in which no infection occurred, the EFI was < 24. The infection model is useful at 8-28.degree. C, and for leaf wetness periods up to 70 h. Daily EFI values were linearly related to rates of disease increase in Michigan [USA] in 1978 and 1979.

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