Modeling Lygus hesperus Injury to Cotton Yields

Abstract

A model of the impact of a lygus, Lygus hesperus (Knight), population on cotton square development and subsequent impact on boll development is proposed. The model is specified as a multistage production process and parameters are estimated using data collected in Kern County, Calif. in 1974. Lygus cause significant injury to cotton during two disjoint periods. The first period occurs during the early squaring stage of the plant when squares are forming at a rate of ca. 100% a week. The second period occurs when the cumulative number of squares per unit area has peaked. The ultimate impact of lygus on cotton yields depends heavily on plants bearing fruit in the early period. Results of computations indicate that lygus can significantly injure the cotton yield in fields with subaverage square loads during the early period. The model can be used to determine economically optimal spraying strategies.