As recently as 2014, My top choices for soybean looper were Belt, Prevathon and Steward. These also included premix products containing pyrethroids, such as Besiege. However based on spray trials over a number of years, I have become concerned about the consistency of diamides (Belt, Besiege and Prevathon) for looper control in the Blacklands. Diamide-containing products have performed moderately in 3 out of 4 recent spray trials in this area (see graphs at the bottom of this article). Let me be clear that the diamides do appear to work well in many Blackland situations, but I have more confidence for consistency of performance with Intrepid Edge, Tracer/Blackhawk and Steward for loopers in this area of the state. As with all insecticides, be sure that you maximize coverage and penetrate the canopy.
Thresholds are 15% defoliation during the reproductive stages and 30% pre-bloom. These include armyworms, bean leaf beetle, green cloverworm, loopers, etc. Be sure to estimate defoliation throughout the entire canopy, not just on the top visible leaves. Loopers tend to defoliate from the bottom up.