Components and Techniques of Integrated Pest Management Threshold Determinations for Aerial Pathogens. Merle G. Eversmeyer, Research Plant Pathologist, USDA-ARS, Department of Plant Pathology, Kansas Agricultural Experiment Station, Kansas State University, Manhattan 66502. Charles L. Kramer, Professor, Division of Biology, Kansas Agricultural Experiment Station, Kansas State University, Manhattan 66502. Plant Dis. 71:456-459. Accepted for publication 3 February 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/PD-71-0456.

Foliar disease forecasting systems have been developed to facilitate efficient use of fungicides in high-disease-hazard situations. Most predictive models use biometeorological “threshold” values to drive the model. These values are not the static control action or economic injury thresholds, as defined in the literature by entomologists and economists. Rather, the values vary with the components of each disease model. Thresholds can be misleading, because the definitions may suggest a level of precision that does not exist in the real world of integrated pest management programs. Normally, threshold determination is straightforward for a single disease system in a crop; however, development of multiple-disease thresholds for a single crop is extremely complex because of the interactions that occur among the disease systems and with yield. Determination of thresholds is limited by constraints of the data available for any given disease system. Spore concentrations, meteorological parameters, disease severity estimates, and biometerological parameters have been used to develop thresholds for models of foliar disease development.