Effects of plant population and plant arrangement on thrips injury to cotton

In Tennessee, thrips rank among the top four insect pests of cotton (Gossypium hirsutum L.), and thrips management is necessary because their feeding injury can lead to delayed maturity and yield loss. Recent observations in small-plot field trials in Tennessee suggest that thrips injury is greater in plots with lower plant populations as well as when plants are isolated compared to being clumped together; however, research documenting this phenomenon is limited. Thus, to investigate plant population effects on thrips injury, a field trial was duplicated at the Research and Education Centers in Jackson and Milan, TN, across two years (2020, 2021). The experimental design was a randomized complete block with split-plot treatments. The whole plots were planted at a density of 2, 4, 8, or 16 per 30.5 cm of row, and the subplots consisted of seed treated with a fungicide or with a fungicide plus an insecticide (5.8 mL/kg of Gaucho^® 600). In 2021, identical field trials were also performed in Jackson and Milan to evaluate thrips injury on clumped and isolated plants. The experiments were arranged in a 2 X 2 factorial with treatments consisting of seed planted with a 64-cell cotton plate to result in a uniform and isolated plant spacing and seed planted with a 48-cell hill drop plate to result in clumped plants. The seed was either treated with a fungicide or with a fungicide plus an insecticide. This research will help growers in Tennessee decide how to use planting procedures to manage thrips.