Both cotton and peanuts are coming up now, and I stopped by some fields today checking for thrips. They are showing up in all fields. Our oldest cotton is showing one true leaf right and peanuts are a little past cracking.
Because thrips are a predictable pest, part of the management is risk. Everything that was planted before now (May 10th) is at greater risk. Also, conventional fields are greater risk for injury. Our at-plant insecticides are still effective. But, there are ways we assess the need foliar applications.
Much of our seed is treated with imdacloprid (Gaucho, Aeris) and thiametoxam (Cruiser, Avicta). We also have in furrow applications of imdacloprid and orthene. Neonic seed treatments (imidacloprid, thiametoxam) are active on thrips for up to 14 – 21 days after planting.
If we have no seed treatment, we need to be in the field checking the first true leaf. This is the best time when we need to apply a foliar application. Once we have 4 true leaves and the plant is growing fast, thrips foliar sprays are not economical.
Thrips injury in cotton
Research has shown that foliar applications are still needed when thrips infestations are high. The best way to make this decision is based on current threshold of: 2 – 3 thrips per plant AND/OR presence of immatures. The immature (wingless) thrips will be yellow/green in color; the adult (winged) thrips are black. Take a white piece of paper and slap a plant on it. Give it a second for the thrips to start crawling. In this field, I have immature thrips present. This suggests are at-plant insecticides are no longer active, and reproduction is taking place.
Immature thrips are lighter in color
We have seen moderate to heavy thrips pressure in the past three years. In peanuts, we are worried about the tramission of Tomato Spotted Wilt Virus. At plant insecticdes (Thimet, Admire) show good efficacy in controlling thrips. (Thimet is the only insecticide shown to reduce TSWV in peanuts). These will also run out of steam and foliar sprays are needed. The symptoms on both cotton and peanuts are cupping of the leaves. In this field, thrips were evident in almost every plant, however, only adults. Timing of foliar sprays is critical. Thrips are feeding in the terminal leaves of peanuts (and cotton), so damage shows up once the leaves come out. Brooks County Agent Stephanie Hollifield writes on the Brooks County Ag Connection, “If you are seeing damage on older leaves, an indicator that thrips are not continuing to die from earlier treatments and/or presence of immature thrips, be prepared for escalating damage of peanut foliage. Within 7-14 days of this scenario, the thrip numbers and damage will dramatically increase. Prior to this occurence, we should scout for thrips and thrips damage and may need to consider an Orthene (acephate) overspray.”
UGA Extension Peanut Entomologist Dr. Mark Abney is monitoring thrips again for the 2016 season. One monitor is in Brooks County. Thrips numbers were down on four of our six traps and slightly up on the other two over the last seven days. The bottom line is that thrips are still moving, and fields where adults have arrived could see injury over the next couple weeks as immatures hatch and feed.