Development of a Weather-Based Advisory Program for Scheduling Fungicide Applications for Control of White Rust of Spinach

ABSTRACT Weather-based advisory programs were developed and evaluated for timing of fungicide applications to control white rust of spinach (Spinacia oleracea) in three field trials using a susceptible cultivar. The advisory programs were based on previous studies that defined periods of temperature (T) and wetness (relative humidity ≥90%, W) that favored disease development. The protectant fungicides mancozeb or maneb (ethylene bisdithiocarbamates; EBDCs) and the systemic fungicide azoxystrobin were applied after 3, 6, 12, 24, and 36 cumulative hours of wetness weighted by temperature (T*W). T*W programs were compared with an advisory program based on 12 h of continuous wetness (12-h W), a 7-day calendar program, and a nonsprayed control treatment. Except for the 3-h T*W program, the number of fungicide applications per trial was reduced for all advisory programs compared with the 7-day program. Averaged over the three trials, applications were reduced from 2.7 per trial for the 6-h T*W program to 3.7 pe...