Dynamic Action Thresholds for Diseases Induced by Nematodes

Pest management involves assessment of pest and crop biology at the population level and an understand'mg of the interaction of organisms at the molecular, cellular, tissue, plant, and population levels. These interactions frequently are sufficiently complex to require simphfication through modeling to allow objective management decisions. The disciplinary orientation of pest scientists often results in development of sophisticated pest or disease models, but somewhat more limited plant models. The models are usually restricted to two biological factors (the crop and a pest or disease), and do not consider the many dynamic interactions of the total agr-ystem. A primary objective of practical agriculture is optimization of the transformation of solar energy into a hawestable yield. This objective is accomplished through crop management, one facet of which is the management of pests as appropriate. Any action taken to manage pests has repercussions throughout the system. A tremendous amount of reductionist research has been accomplished in all pest disciplines; however, optimization of yield will require a holistic approach to crop systems to explain and understand the interactions at the population level. The implicit suggestion of additivity of estimates of individual pest losses in crops is not valid, as frequently discussed (1 1, 14, 16). One alternative is to use multiple regression techniques, resulting in discounting coefficients for interactions among different pests (18). More analytical solutions include synoptic approaches (22, 27). Because of the interest or expertise of the modeler, a conceptual error frequently confounded in models of crop losses by pest organisms is consideration of the pest as the focus of the