Developing An Action Threshold for Thrips in the Texas High Plains

Thrips are a significant economic pest of cotton during the pre-squaring stage of growth and development in most of the cotton growing areas of the United States.  On the Texas High Plains, the western flower thrips, Frankliniella occidentalis (Pergande), is the predominate thrips species comprising 80-95% of the population infesting cotton.  In irrigated cotton where thrips populations are historically high many growers opt to utilize preventative insecticide treatments such as in-furrow applications or seed treatments to control thrips.  However, where thrips populations are not “guaranteed” to be especially troublesome, preventive treatments may not be necessary and represent an unnecessary expense.  In these situations, well timed banded foliar insecticide applications for thrips control may be more profitable.  In this study we studied the impact of different foliar spray intervals targeting thrips in seedling cotton on yield.  Using this data we hope to develop a robust action threshold for management of thrips in seedling cotton with foliar insecticides.  In 2007, temperatures were cool (low 50s to low 80s ^oF) and we observed a significant yield reduction due to thrips impact during the first two week following plant emergence.  Correlation analysis suggested that the current action threshold of 1 thrips per true leaf is too high under these environmental conditions, and that the threshold should probably be closer to 0.5 thrips per plant.  In 2008, temperatures were much warmer than in 2007, and despite greater thrips densities in 2008, there was no observable impact on yield.  Under warm conditions, (high 50s to low 90s ^oF) the current action threshold appears to be too low.  The 2009 tests have not been harvested at time of submission.