|Chu, Chang Chi|
Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 1996
Publication Date: N/A
Interpretive Summary: A fundamental aspect of integrated pest management is pest insect populations should only be controlled if the damage they cause is more expensive than cost of the control methods implemented. This seemingly simple decision rule is complicated by changing crop price, variable control costs, variable efficacies associated with control, and dynamic relationship between pest density and crop damage. Sweetpotato whitefly, Bemisia tabaci, is a key pest of cotton in the southwestern U.S. and has potential to reduce yield and lint quality without proper control. Efficient and reliable sampling methods have been developed to monitor whitefly populations, but research is still needed to define the levels of pest density that cause economic damage. This study was undertaken to quantify the relationship between pest density and yield and use this information to develop rational decision-making protocols (economic injury levels, EIL) for pest control. EILs declined with increasing cotton prices and increased as cost of control increased, however, these changes were relatively subtle based on typical ranges in price and control costs. The efficacy of control provided by insecticide applications dramatically influenced EILs, with lower efficacies being associated with higher injury levels. A multiple regression model was developed to calculate EILs in relation to dynamic changes in crop price, control costs, control efficacy and potential yield.
Technical Abstract: Field studies were conducted during 1993-1994 in the Imperial Valley, CA and Maricopa, AZ to examine relationships between densities of Bemisia tabaci populations and cotton yields, and to estimate economic injury levels for pest management application. Populations of B. tabaci were manipulated through differing intensities of insecticide applications in replicated plots. Resulting insect populations and measurements of cotton lint yield were used to develop damage functions and to estimate economic injury levels for all life stages in relation to variable cotton prices, insecticide costs, and pest control efficacy. Economic injury levels declined with increasing cotton prices and increased as the cost of control increased, however, these changes were relatively subtle based on typical ranges in price and control costs. In contrast, the efficacy of control provided by insecticide applications dramatically influenced economic injury levels, with lower efficacies being associated with higher injury levels. We developed a multiple regression model that accounts for the dynamic changes in the economic injury level in relation to crop price, control costs, control efficacy and potential yield. Based on average prices and reasonable control costs and efficacy, economic injury levels ranged from 5.9-15.2 adults/leaf, 6.1-19.8 eggs/cm sq., and 1.7-4.7 nymphs/cm sq. Additional research is needed to more clearly relate the costs of control to the suppression of insect populations.