MODELING CROP LOSSES AT THE FIELD-SCALE

The approaches for modeling yields of crops in relation to plant disease intensity are reviewed. It is shown how these models can be expanded or modified to account for: i) duration of healthy leaf area during a growing season and the interception of radiation by leaf area; ii) spatial pattern of pathogens or diseases and resulting mean yield; and iii) time of infection of plants (especially by viruses and other organisms that cause systemic infection) linked to the temporal dynamics of disease incidence in fields. These expansions or modifications can make predictions of crop losses more precise or increase our understanding of the disease/loss relationship. Areas where more research is needed are discussed, especially: i) dealing with error in measuring disease intensity; ii) validating models; and iii) relating yield to multiple diseases or pests.