South Carolina Cotton: Thrips – Seed Treatments and Foliar Applications

We continue to focus on management of thrips. Hopefully, you have been able to get some of your crop planted. It has been wet for a couple of weeks, and the rains are not letting up again to end this week. Weed control passes will be delayed, as will sprays for thrips.

Remember, applications of insecticide for thrips after the 4-5-leaf stage are almost always “revenge killing” sprays that don’t pay for themselves. Our research has shown that the best time to spray for thrips is when they meet or exceed threshold during the 1-2-leaf stage.

When cotton is planted after May 20, seed treatments have proven to be effective in limiting thrips damage to seedling cotton plants. Avicta (with abamectin) and Aeris (with thiodicarb) have some activity on nematodes. The high rate of aldicarb should also provide some protection against nematodes and suppress early populations of aphids and spider mites.

Generally, a preventative insecticide used at planting will protect seedlings from severe stunting characteristic of thrips injury. Occasionally, however, conditions will be unfavorable for proper uptake of systemic insecticides (too cool, dry soil, excessive moisture, etc.), and plants can be severely damaged.

Foliar treatments will be most effective when applied to cotton seedlings prior to unfolding of the second true leaf. A foliar insecticide treatment may be needed when two or more thrips are found per plant. Shake each plant (randomly select 25 or more) into a coffee cup or a similar utensil to facilitate counting. When most plants have severely damaged growing points and immature thrips are present, one or more foliar treatments may be needed to allow the plants to resume normal growth and development.

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Examine plants 5-7 days after the initial treatment, and treat again if immatures are still present on most plants. When the newly unfolded leaves of infested plants are free of damage, and plants appear to be growing at a normal rate, further applications of insecticides will have little benefit.

Treatments applied beyond the four-leaf stage of growth may actually be counterproductive, as these would likely reduce beneficial populations and result in early-season problems with other pests. Although effective, acephate can flare populations of spider mites and aphids.