Thrips-O-Plenty, Cotton And Soybeans

JACKSON, TENN.
   A number of private consultants have already commented on high thrips pressure this year, some as high as 6-12 thrips on cotyledon and one leaf plants. This high pressure is a common theme across much of the Belt this year. Repeating from last week …. the risk of thrips causing yield loss increases as the time between planting and cotton reaching the second or third true leaf stage increases. Keep track of the days elapsed between emergence and seeing the first true leaf. Consider applying insecticide before the second true leaf if it takes longer than 14 days after emergence before the first true leaf is visible. Certainly apply a foliar insecticide if the first true leaf is showing significant signs of thrips injury (pictured left). Seed treatments will provide protection for about three weeks following emergence, but injury can occur when multiple adult thrips are present per plant. The insects have to feed before they die.
   The standard treatments for thrips in cotton are listed below.
       Orthene or acephate @ 0.20 lb ai/acre
       Bidrin 8E @ 2.5-3 oz/acre
       Dimethoate 4E @ 6 oz/acre*
   Dow AgroSciences also has a new product called Radiant SC. In my somewhat limited testing, it has provided similar control to the above standards. The active ingredient is spinetoram, which is closely related to spinosad (i.e., Tracer). Radiant has a 2(ee) label for the suppression of thrips in cotton at a rate of 1.5 – 3.0 oz/acre. A good starting point would be 2 oz/acre, but in my experience the inclusion of an adjuvant is critical to achieve the best results. I suggest a non-ionic surfactant at a rate of 0.25% V/V. Radiant appears to have relatively good activity on western flower thrips. It is less impactful on beneficial arthropods, so there may be a reduced risk of flaring spider mites or aphids. On the downside, it will likely be more expensive than the traditional alternatives.
   • More so than the other options, Dimethoate may cause some leaf burn similar in appearance to Dual injury. For this reason, I normally do not recommend Dimethoate if it will be coapplied with Dual or Dual-containing premixes. I would also hesitate before applying Dimethoate with Ignite on Phytogen 375 WRF or any other WideStrike cotton variety because of the risk of compounding leaf burn.
   SOYBEAN: Should you treat for thrips in soybean? As a general rule of thumb, this practice is not recommended because soybean seedlings can tolerate much higher thrips populations than cotton. It is very unlikely that spraying for thrips would be justified on anything with an insecticide seed treatment. There is no formal threshold for treating thrips in soybean. You should consider multiple factors, but the primary thing to consider is the general vigor of the plants. Rest assured if plants look healthy and are growing well. You might consider treatment if small seedlings are already stressed, growing poorly, and there are many thrips per plant. This should be the exception and not the rule.
   Note: thrips injury in soybean is not nearly as evident as on cotton. It takes very large numbers to cause leaf deformation/puckering in soybean. More typically, thrips injury will cause some whitening of leaves, especially around the veins. In the past, I’ve been on calls where thrips were being blamed for injury that was caused by pre-plant applications of dicamba (which looks similar to thrips injury in cotton). Having a few thrips per plant will not cause this symptomology. If treatment is needed, Orthene or Acephate (0.2 lb ai/acre) or relatively low rates of most synthetic pyrethroids should provide
decent control. Δ
   DR. SCOTT STEWART: IPM Extension Specialist, University of Tennessee

Typical thrips injury on soybean.

Thrips injury on cotton.