The Interaction of Pre Emerge Herbicides and Insecticide Seed Treatments and Its Effects on Early Season Cotton

Thrips (Frankliniella fusca and Frankliniella occidentalis) are one of the most important pest families during the early growing season of Mid-south, U.S. cotton (Gossypium hirsutum L.). In most years it is not uncommon to over spray 20-30% of cotton acres for thrips.  However, within the last two years, thrips pressure has increased.  In 2011 and 2012 more than 70% of cotton acreage was over sprayed for thrips control, independent of insecticide seed treatments. In this early development stage of cotton, growers have noticed that pre emerge herbicides have an effect on early season cotton growth.  With insecticide seed treatments not working as well as they have in the past, many growers have questions about seed treatment efficacy. This experiment was designed to investigate the interaction between insecticide seed treatments and pre-emerge herbicides, how this interaction effects cotton growth, and how this interaction effects efficacy of seed treatments on thrips. Plots were planted in a randomized complete block design, measuring 50 ft. by 4 rows. Two commonly used insecticide seed treatments and a control were then crossed with 3 commonly used pre emerge herbicides and a control making a 3x4 factorial.  Measurements of thrips populations were recorded 3 times at 7, 14, and 21 days after emergence. Injury by herbicide was recorded at 7 and 14 days after emergence in the two categories of chlorosis and necrosis.  Thrips damage was recorded. Plant heights and stand counts were taken each week until bloom. Changes in maturity were determined by taking nodes above white flower counts. Yield will be taken, eventually.