Effects of plant density, seed spacing, and seed treatment on thrips injury to cotton

• Published in: Crop protection 2022-11, Vol.161, p.106059, Article 106059
• Main Authors: Krob, Jessica L., Stewart, Scott D., Brown, Sebe A.
• Format: Article
• Language: English
• Subjects: Cotton; Plant density; Thrips
• ISSN: 0261-2194; 1873-6904
• DOI: 10.1016/j.cropro.2022.106059

Previous observations in small-plot field trials in Tennessee suggest that thrips injury is higher in plots with lower plant densities and when singular plants are spatially isolated and uniformly distributed compared to a group of plants that are clumped together; however, research documenting this is limited. Thus, studies were performed in Jackson and Milan, TN across two years (2020, 2021). Both studies had fungicide-treated seed planted with or without an imidacloprid insecticide seed treatment. The first study investigated the effects of plant density by planting seed at rates considered to be low, normal, high, and very high. The second study investigated the effects of seed placement strategies with seed planted at the same density. Cotton plates were used to plant seed to result in singular plants that were spatially isolated and uniformly planted or clumped, “hill-dropped” plants. Results from the plant density tests showed thrips injury ratings were higher as the plant density decreased. At two test sites, the number of adult thrips was higher in plots with lower plant densities, indicating that thrips were more concentrated on individual plants. However, high thrips pressure and unfavorable growing conditions at the other sites seemed to overwhelm the potential effects of plant populations. Results from initial thrips injury ratings in the seed spacing study showed significantly higher injury for singular, uniformly distributed plants than plants in a hill (i.e., cluster); however, additional research is needed because one test was lost. Future research evaluating oviposition rates on recently emerged seedlings could help explain why decreased thrips injury occurs when plant densities are relatively high. •Lower plant densities had higher plant mortality and injury with lower yields.•Plant spacing could potentially be utilized to reduce thrips injury in cotton.•Oviposition rates may explain higher thrips injury in lower plant densities.