Infection Model for Timing Fungicide Applications to Control Cherry Leaf Spot. 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. Plant Dis. 65:955-958. Accepted for publication 31 March 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-955.

A model relating leaf wetness duration and mean air temperature to infection of sour cherry by Coccomyces hiemalis was evaluated for timing applications of fungicides dodine and CGA-64251 (1-[[2-(2,4-dichlorophenyl)-4-ethyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole) for leaf spot control. Infection periods were identified and classified as low, moderate, and high based on predicted environmental favorability indexes of ≥14, ≥28, and ≥42, respectively. In 1979 and 1980, CGA-64251 provided good leaf spot control regardless of application timing, and dodine provided good control when applied after low and moderate but not after high infection periods. In a second trial in 1980, dodine and CGA-64251 applied on an 11-day schedule or as postinfection applications after infection periods with an environmental favorability index ≥28 gave comparable control. Secondary infection was prevented with eradicant sprays applied against conidial inoculum available during infection periods. Use of the infection model for timing sprays for leaf spot is a promising alternative to fixed time interval spray schedules.

Keyword(s): disease forecast, epidemiology, Prunus cerasus.