In field experiments with the Embrapa 16 wheat cultivar, carried out in Passo Fundo and Não-Me-Toque counties, in 1999 and 2000, the grain yield was negatively related to foliar rust incidence, foliar rust severity, the number of rust pustules per square centimeter, and the area under the disease progress curve. In contrast, there was a direct relationship between grain yield and the reflectance of solar radiation (810 nm) measured by a radiometer. The damage model equations obtained by regression analyses of disease and reflectance to yield were used to determine economic damage thresholds (EDTs) for the control of leaf rust in different plant growth stages. The yield reduction associated with leaf rust averaged 40%, with a maximum of 43%. The reflectance at 810 nm was related to grain yield, disease severity, and the number of pustules.
Disease assessment; economic damage threshold; radiometry
