The conventional economic injury level is defined as the lowest insect population density that will cause economic damage, while the economic threshold is the population level where insect control should be initiated to avoid exceeding the economic injury level. Cotton (Gossypium hirsutum L.) production faces multiple insect pests, multiple stresses and new developments such as transgenic cotton that make an economic injury level based on insect populations less practical. The application of an economic threshold in cotton pest control decisions suffers from the lack of an economic injury level to confirm those decisions. This paper proposes an economic injury level model based on plant injury (square shed frequency). The model uses control costs, crop value, dynamic plant-monitoring results and cotton's compensation capacity for early-season loss to calculate a break-even injury level for first flower. The break-even level is transformed into a shed rate limit for stage of plant development, against which producers can compare the actual shed rate at any time prior to first flower. A shed rate below the limit indicates that initiated control prevented pests from causing economic injury while a shed rate above the limit indicates that the economic threshold was inadequate to prevent an increasing infestation from causing economic damage. The plant-based economic injury level is intended to not only verify insect management decisions but also help recognize more efficient and comprehensive economic thresholds. The economic injury level model has been incorporated into the COTMAN computer program to facilitate implementation by producers.
