Thrips earn major pest status in North Carolina

As North Carolina cotton producers can attest, we and our neighbors from Virginia must contend with higher thrips levels and potential damage than anywhere else in the Cotton Belt. In a series of 50 or so replicated tests conducted here and in Virginia during the past decade, untreated cotton lost an average of approximately 300 pounds of lint compared to the best at-planting treatments — more often than not either Temik 15G at 5 pounds per acre or a seed treatment followed by a first true leaf foliar spray.

Unfortunately, our often cool, wet seedling grow-off conditions, coupled with a very high ratio of thrips host acreage to small average cotton field size (approximately 15 acres) and high thrips levels, often seem to create a ‘perfect storm’ of thrips headaches.

Very hot, dry weather can also result in such high levels of migrating thrips that on untreated cotton can sometimes reach upwards of 50 to 75 immature thrips per plant.

Timely aggressive control of this troublesome pest complex is often an important component of profitable cotton production here. An early, vigorous cotton crop triggers earlier fruiting, helps set the stage for mid- to late-season insect management opportunities (such as lower potential boll damage from stink bugs), and often allows more effective defoliation and earlier harvest.

  • Gaucho Grande vs. Cruiser Seed Treatment: At both the prior and the more recent higher rates, Gaucho Grande and Cruiser have provided similar control of thrips, nearly identical reductions in plant damage, and similar stand counts, plant heights, dry weights, fruit set, maturity and yield.
  • A word of caution: With either of these products, expect no more than approximately three weeks of thrips control from the date of planting. To extend this short residual activity, foliar application following a seed treatment — the closer to the first true leaf stage the better, and no more than 3 to 3.5 weeks after planting.

    Although it seems on the early side, a cotyledon stage spray is probably far better timed for thrips than a second or third true leaf stage application. In most cases (though certainly not always — seen in 2005 and 2006), a single application at the first true leaf stage provides cotton seedlings with enough thrips protection time to get the plants “over the hump”, thus reducing further thrips vulnerability and often extending into a period of fewer migrating thrips.

  • Insecticide Seed Treatment vs. Temik: A seed treatment followed by the above timed foliar application typically provides thrips control and plant growth similar to 5 pounds of Temik 15G in soils without economic levels of nematodes.
  • A seed treatment followed by a foliar spray to seedlings later than the first true leaf stage usually gives the advantage to Temik. Under conditions of poor uptake, a possible foliar application following Temik should be based on the finding of crinkled (or possum-eared) newly forming young leaves and deformed or darkened buds along with the presence of immature thrips.

  • Avicta and Aeris Seed Treatments: Based on three years of evaluations in North Carolina, Avicta seed treatment (Cruiser + abemectin for nematodes + Dynasty, a 3-way fungicide) and Aeris (Gaucho Grande + thiodicarb for nematodes + fungicides put on either by a dealer or already on the distributed product) usually provides nematode control similar to Temik 15G at 5 to 6 pounds. Until further testing, the level of thrips control provided by these products should be considered identical to Cruiser or Gaucho Grande alone, thus the same need for a foliar spray.
  • Western Flower Thrips: We have 5 to 7 thrips species that are found on cotton seedlings, most commonly tobacco thrips. Most species are well controlled with at-planting and/or foliar insecticides, unless migrating adult and established immature thrips are present at very high levels.
  • Unfortunately, difficult to control western flower thrips sometimes make up a portion of the overall thrips population. This species is both difficult to control with seed treatments and with foliar applications at conventional rates (i.e., Orthene 97 at 0.25 pound active ingredient per acre).

    For example, in a 2006 test near Rocky Mount, Temik alone at 5 pounds of product per acre controlled 63 percent of adult western flower thrips compared with 30 percent control with the seed treatments plus an Orthene spray at 4 weeks after planting. Control of adult tobacco thrips at this time was 100 percent with Temik and 96 percent with the seed treatment plus Orthene.

  • Cotton Aphid and Spider Mite Increases: In a 2004-2005 Independent Crop Consultants’ Survey, of the consultants reporting 100 percent Temik use by approximately 150 cotton producers, 6.8 percent of their cotton acreage was treated for cotton aphids. The producers of consultants reporting an average of 75 percent seed treatment use (usually followed by a foliar spray for thrips) sprayed 15.7 percent of their cotton acreage for cotton aphids, a 2-fold increase.
  • With spider mites, although overall spraying was less, the difference was more dramatic, with the high Temik users treating 0.58 percent of their cotton acreage for spider mites and seed treatments users (seed treatment + foliar spray) treated 5.3 percent of their acreage, a difference of approximately 9-fold. Cotton producers electing to use the seed treatment plus foliar spray route should be on the alert for greater potential economic infestations of the above pests.

  • Late Planted Cotton: In cotton planted after approximately May 15-20 in North Carolina, a seed treatment alone or Temik 15G at the lower 3 pound product rate usually provides adequate thrips control due to quicker seedling grow-off and generally declining thrips levels in the two to three weeks following this late planting.
  • All Clear: In essentially all of our research trials, when the cotton plants have an average of approximately 5-6 true leaves with adequate moisture levels and reasonably warm weather, thrips control should no longer be necessary.
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