In Louisiana and the cotton belt, thrips are considered the No. 1 early-season pest of seedling cotton. Tobacco thrips compose the primary species infesting Louisiana cotton, while western flower thrips are often present at lower numbers. With the absence of Aldicarb (although we now have a commercially available Aldicarb replacement named AgLogic), insecticide seed treatments now dominate the early-season cotton insect pest management landscape.
As of 2020, there are only two seed treatment options: acephate and neonicotinoids. Imidacloprid and thiamethoxam are the two most commonly used neonicotinoids. These treatments are offered alone and in combination with nematicides.
Based on bioassay data generated in the past eight years, the LSU AgCenter does not recommend thiamethoxam alone as a seed treatment for cotton. This is due to the formation of resistance by tobacco thrips. However, imidacloprid is still effective, and when used in conjunction with the insecticide-nematicide thiodicarb (Aeris), it provides very good control of thrips.
If Aeris is not an option, imidacloprid overtreated with acephate (6.4 oz/cwt) is another viable option. Acephate alone will control thrips; however, acephate has a significantly shorter residual period than imidacloprid. The probability of having to return with a foliar application is very high. Also, if you elect to overtreat cotton seed with acephate, the seed cannot be returned.
In-furrow applications of imidacloprid also work very well controlling thrips. Four-pound imidacloprid at 9.2 oz/acre or 2 lb material at 19.0 oz/acre provide excellent control of thrips. AgLogic has demonstrated satisfactory control of thrips at the 3.3 and 4 lb/acre rate.
Lastly, foliar rescue treatments are also an option. Foliar treatments should be made when immature thrips are present and/or when large numbers of adults are present and damage is occurring. Seedling cotton will typically always have a few adult thrips, but the treatment trigger is the presence of immatures.
The presence of immature thrips often signifies the insecticide seed treatment has lost its efficacy and reproduction is occurring. Avoid spraying solely based on plant injury because the damage has already occurred. Be aware that residual herbicides and sandblasting injury can mirror thrips injury.
Below are some considerations when deciding what foliar insecticide to use.
Positives: Relatively inexpensive, decent efficacy at high rates, less likely to flare spider mites and aphids than acephate.
Negatives: Less effective on western flower thrips, less effective than acephate or bidrin when applied at lower rates.
Positives: Relatively inexpensive, effective on western flower and tobacco thrips.
Negatives: May flare spider mites and aphids if present.
Positives: Effective, less likely to flare spider mites and aphids than acephate.
Negatives: More expensive, less flexibility with applications early season.
Positives: Effective, unlikely to flare spider mites and aphids. Intrepid Edge is a mix of Radiant and Intrepid. Activity is similar to Radiant.
Negatives: Requires the application of two modes of action but only gets the benefit of one.
Insecticide choice depends on a number of factors such as cost, impact on secondary pests and spectrum of thrips species present. If a foliar thrips treatment is justified, do not wait for a herbicide application and only spray when necessary to avoid flaring spider mites and aphids.