Interactive Effect of Cover Crop, Irrigation Regime, and Crop Phenology on Thrips Population Dynamics and Plant Growth Parameters in Upland Cotton

Abstract

Cotton (Gossypium hirsutum) requires a long growing period for fruit and fiber maturation, making it vulnerable to insect pests, thus affecting the seed cotton yield and fiber quality. Cotton-feeding thrips (Thysanoptera: Thripidae) are one of the major insects impacting cotton yield throughout the U.S. cotton belt and worldwide. A two-year field research conducted at Texas A&M AgriLife Research farm in west Texas, USA quantified the interactive effect of three cover crops [wheat (Triticum aestivum), rye (Secale cereale), and no cover] and three irrigation regimes [rainfed, deficit irrigation (30%) and full irrigation] on thrips population dynamics across the phenologically susceptible stages of upland cotton and resulting impact on plant growth and yield parameters. Temporal densities of thrips, feeding injury from thrips, cotton growth and reproductive profiles, yield, and fiber quality varied with cover crops and irrigation levels. Thrips densities were conspicuously low due to harsh weather conditions, but the densities decreased with an increase in plant age. Terminated rye and wheat cover versus conventional-tilled, no-cover treatments showed marginal effects on thrips colonization and population dynamics. Similarly, full irrigation treatment supported higher thrips densities compared to rainfed and deficit irrigation treatments. Immature thrips densities increased through the successive sampling periods, indicating increased thrips reproduction following the initial colonization. Thrips feeding injury was significantly greater in no-cover plots in the early seedling stage, but the effect was insignificant across all cover crop treatments in subsequent sampling dates. The results of this study demonstrated increased seedling vigor, plant height, and flower densities in terminated cover crop plots across all irrigation regimes compared to that in no-cover plots. However, the cover crop x irrigation interaction significantly impacted the cotton lint yield, with increased lint yield on cover crop treatments. This study clearly demonstrates the value of cover crops in semi-arid agricultural production systems that are characterized by low rainfall, reduced irrigation capacity, and wind erosion of topsoil.