Don’t expect more than a few days of residual control with these treatments, but you will see downstream benefits by reducing populations of immature thrips. The immature stages of all thrips are light colored, but so are the adults of several other species including onion thrips, eastern flower thrips and western flower thrips. 

My observations indicate that tobacco thrips are the predominant species present, but this may vary across the state.

So how do you know if you are dealing with western flower thrips? Because immature thrips are nearly impossible to tell apart, you must rely on adult ID and some detective work. You will need a good hand lens.

• Adult tobacco thrips will be nearly black. Adult western flower thrips will be light colored… sometimes described as having an orangish tint. Look for wings to confirm you are looking at the adult stage.

• The presence of immatures, lacking wings, on cotyledon or 1-leaf cotton is a sign of western flower thrips because this species is not well controlled by insecticide seed treatments. Cruiser will typically look a little better than Gaucho if western flower thrips are the predominant species.

• The presence of immatures within a few days following an application of Acephate, Bidrin or Dimethoate is also a sign of western flower thrips. However, finding adults within a few days after an application is not uncommon if there is a large migration occuring, and thus, not necessarily a sign of western flower thrips.

Radiant, which is more expensive, does not seem necessary based on what I’m seeing and reports from the field. However, there may be an advantage to using Radiant for follow-up applications if thrips pressure continues: 1) it is relatively soft on beneficial insects and less likely to flare secondary pests compared with multiple applications of other insecticides, and 2) thrips surviving a first application are more likely to be western flower thrips because Acephate, Bidrin and Dimethoate do not work especially well on this species.

What about soybean? Soybeans are not nearly as susceptible to thrips as cotton, which is good because populations are also typically higher on soybean. 

Do not use cotton thresholds!  Treatment is only occasionally needed in soybeans (and very unlikely if an insecticide seed treatment was used). Exceptions prove the rule, and there are examples where foliar insecticides or seed treatments have improved yields when thrips were the only obvious pest present. 

I am not morally opposed, but I would only treat soybeans for thrips when plants are small (prior to the first trifoliate), plants are growing poorly, and thrips are very common.

Leaf cupping, as seen with cotton, is not a typical response to thrips injury in soybeans unless populations are extremely high. Indeed, leaf cupping in soybeans often indicates herbicide injury (e.g., dicamba).