Integration of Host Resistance and Weather-Based Fungicide Scheduling for Control of Anthracnose of Tomato Fruit. BRUCE A. FULLING, Graduate Student, Department of Botany and Plant Pathology;; Purdue University, West Lafayette, IN 47907. E. C. TIGCHELAAR, Professor, Department of Horticulture; and RICHARD LATIN, Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Plant Dis. 79:228-233. Accepted for publication 4 November 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0228.

The relationship between anthracnose resistance of tomato cultivars and disease incidence at various fungicide application intervals (determined by a weather-based scheduling program) was evaluated in field studies in 1992 and 1993. The resistance of tomato cultivars was indexed relative to the disease response of a standard susceptible cultivar in evaluations conducted in a disease nursery. Five different fungicide application intervals, based on action threshold values determined by the TOMCAST program (12, 16, 20, 24, or 32 daily severity values), were tested on five tomato cultivars that represented a range of resistance currently available in commercial production. The relationship between application interval and disease incidence was determined by linear regression techniques for each cultivar. The slope of the regression for each cultivar was designated as a TOMCAST anthracnose coefficient (TAC). TAC values were regressed on resistance indices to estimate optimum fungicide spray intervals for cultivars with different degrees of resistance. Results indicated that, with the TOMCAST program, resistant cultivars require three to four fewer fungicide applications per year than susceptible cultivars to obtain adequate control of anthracnose. Optimum action threshold values may be increased from current recommendations by at least two-fold for resistant cultivars currently under development.