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Possible Large Thrips Flight

This is Jack Bacheler Extension Entomologist at North Carolina State University with the May 16 Cotton Insect Update.

Both observations from several individuals during the past few days and Dr. George Kennedy’s tobacco thrips weather model suggest that our major thrips generation will be moderate to large, with possible peaks for most of our cotton production areas coming during the next 10 days or so depending on location (for example May 24 for Goldsboro and May 29-30 for Rocky Mount and Plymouth). Of course, if this prediction holds, that does not translate into minimal thrips damage after the adult peak. High levels of migrating adults simply mean that many immatures are likely to follow in unprotected cotton. Even on tobacco and soybean, thrips levels appear to be higher than in most recent previous years. At Rocky Mount yesterday, our seedlings averaged approximately 6 adult thrips per plant behind seed treatments at 2 weeks after planting. This level of adults, along with the very low levels of immatures found, indicated that the seed treatments were still holding. However, a level of 6 adult thrips per plant can be damaging in their own right, so plants should be assessed for thrips adults and immatures and damage to the bud area and treated accordingly. In many cases, a foliar spray may be needed at either three weeks after planting when the seed treatment effectiveness has run out, or at the first true leaf stage when cotton seedlings are at their most susceptible stage for thrips damage. Cotton planted after May 20 may escape much of this damage.

Our recent wetter, cooler weather has no doubt suppressed levels at least temporarily, but this can change seemingly overnight when and if warmer sunny weather resumes. In general, our hard-to-control western flower thrips often become a problem on cotton somewhat later than our more common tobacco thrips. In most cases, the levels of “westerns” on cotton are lower when we have good rainfall patterns and are higher when we experience extended hot dry weather. We should also point out that in most situations easier-to-control tobacco thrips are far more common that “westerns”, though that’s not much consolation to producers who must sometimes deal with this pest. Because correct thrips species identification requires an expensive high powered microscope, and considerable time and expertise, the first time most producers are aware that they may have westerns is when extremely poor thrips control follows a foliar spray for thrips. For now, a high expensive rate of Radiant insecticide is essentially the only labeled insecticide that appears to provide good control of westerns. A number of tests are underway in the Southeast to determine if lower, more affordable rates of Radiant are also effective against “westerns”. In most cases with westerns, we keep our fingers crossed that the “thrips safe” five true leaf stage comes along as quickly as possible.

Kudzu bugs have begun showing up in low to high levels on volunteer soybean plants in most soybean production areas of the state, and in what we hope are relatively low levels on early-planted current crop beans. We’ll provide more information on this situation in next week’s Pest Patrol when we get a better fix on actual kudzu bug levels per plant or per sweep in some of these fields, and if these levels may impact yield. We do not expect the major kudzu bug flight from kudzu until at least the last week in July.