INTEGRATION OF HOST-RESISTANCE AND WEATHER-BASED FUNGICIDE SCHEDULINGFOR CONTROL OF ANTHRACNOSE OF TOMATO FRUIT

The relationship between anthracnose resistance of tomato cultivars an d disease incidence at various fungicide application intervals (determ ined by a weather-based scheduling program) was evaluated in field stu dies 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 TOM-CAST program (12, 16, 20, 24, or 32 daily severity values), we re tested on five tomato cultivars that represented a range of resista nce currently available in commercial production. The relationship bet ween application interval and disease incidence was determined by line ar regression techniques for each cultivar. The slope of the regressio n for each cultivar was designated as a TOM-CAST anthracnose coefficie nt (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 TOM-CAST program, res istant cultivars require three to four fewer fungicide applications pe r year than susceptible cultivars to obtain adequate control of anthra cnose. Optimum action threshold values may be increased from current r ecommendations by at least two-fold for resistant cultivars currently under development.