Cotton planting started last week and here is some coming up on the east side of the county. Plants are emerging with either cotyledons present or cotyledons + first true leaves emerging. So far, plant stands look good. Both of these fields are irrigated. We are running out of moisture in dryland fields – especially conventional till. In fields were tillage has been minimum or a cover crop exists, we still have some moisture.
I wanted to check for thrips. They will initially feed on the lower surface of cotyledons and then in the terminal bud of each developing seedling. We expect to see higher thrips infestations on early planted cotton in conventional tillage systems.
Foliar Application Threshold
Many at-plant insecticides are used including in-furrow sprays and seed applied systemics. This is good, but we still need to be aware of conditions favoring thrips. For fields planted after May 10 or where reduced tillage is used, the risk of high thrips infestations is lower. Our threshold for thrips to use foliar insecticides – with or without at-plant insecticide – is when 2-3 thrips per plant are counted and/or immatures are present. The immatures (without wings) are yellow. The presence of immatures means at-plant insecticides are no longer active. (The best way I learn to scout thrips is take a small piece of white paper, and hold it under the plant. Flick the plant over the paper, and you will see thrips crawling on the paper.)
I counted thrips in a few fields yesterday and found no immature thrips. On average, I observed 1 per seedling. This is nearing threshold, but good to see no immatures present. Something to consider is our warm growing conditions now. Seedlings become more tolerant of thrips feeding as they develop, and a fast growing seeding can better tolerate thrips feeding. A plant that is under stress from cold or herbicide is more likely injyred by thrips since it stays in that young stage.
However, negative impacts of warm weather is our winter crops drying down. I am seeing this in the field now. Once our rye, ryegrass, etc. dries down, thrips will move to something green to reproduce. UGA Extension Entomologist Dr. Phillip Roberts expects it to be a normal year for thrips; therefore, we need to be scouting fields and preparing for foliar applications.