Evaluation of PRE Herbicides and Seed Treatment on Thrips Infestation and Cotton Growth, Development, and Yield

Since 2011, foliar treatments for thrips in cotton have increased to nearly two applications per acre on 75% of total acres in spite of these acres being planted with seed treated with an insecticidal seed treatment. Additionally, glyphosate resistant Palmer amaranth has become problematic for Mississippi producers. As a result, the use of preemergence herbicides has increased dramatically since 2008. From 2008 to 2012 the number of cotton bales lost due to thrips damage increased from 152 bales lost in 2008 to 5,057 bales lost in 2012. In cotton, both thrips damage and PRE herbicides can interfere with emergence and early season growth. Previous research on thiamethoxam and imidacloprid has shown both to be effective in controlling thrips in cotton. Given the increased use of PRE herbicides in Mississippi cotton production, it has been suggested that PRE herbicides may be contributing to the increase in thrips populations over the past several growing seasons. Therefore, the objective of this research was to evaluate the use of PRE herbicides and seed treatments on thrips populations as well as cotton development and yield. This study was conducted at three locations in Mississippi which included the Black Belt Branch Experiment Station near Brooksville, the R.R. Foil Plant Science Research Center near Starkville, and the Delta Research and Extension Center in Stoneville. Seed treatments included thiamethoxam fungicide, imidacloprid fungicide, and fungicide only. PRE herbicides included Cotoran 4L at 32 fl oz/ac, Direx 4L at 32 fl oz/ac, Reflex at 16 fl oz/ac, Dual Magnum at 16 fl oz/ac, Dual Magnum Cotoran 4L at 16 32 fl oz/ac, respectively as well as an untreated check. This experiment was conducted using a factorial arrangement of treatments in a randomized complete block design, with the two factors being PRE herbicide and seed treatment. All data were subjected to analysis of variance and means were separated using Fishers Protected LSD at p 0.05. Cotton seed treated with imidacloprid had significantly less injury from thrips than cotton seed treated with thiamethoxam and fungicide only treatments. Thrips counts at the four leaf stage indicated significantly greater infestation on cotton treated with thiamethoxam compared to cotton treated with imidacloprid. Cotton seed treated with imidacloprid resulted in significantly taller cotton plants throughout the season than those grown from thiamethoxam treated seed. Averaged across all seed treatments, cotton treated with Reflex was significantly shorter than all other PRE herbicide treatments at the 4 leaf stage, pinhead square, first bloom, and harvest. Cotton treated with imidacloprid produced the highest yields. Averaged over all PRE herbicides, cotton seed treated with imidacloprid yielded 1223 lbs/ac whereas cotton seed treated with thiamethoxam producing yields of 1188 lb/ac. PRE herbicide also had an effect on seed cotton yields, with cotton treated with Reflex yielding significantly lower than all other PRE herbicides. Cotton treated with Direx 4L, Cotoran 4L, and Dual Magnum Cotoran 4L yielded 1189 to 1226 lbs/ac whereas cotton treated with Reflex yielded 1110 lbs/ac.