Soybean loopers are a migratory pest that we sometimes see in soybeans late in the season. Numbers really picked up in our research plots in the Sandhills region of the state and we’ve picked up more and more in the Blacklands region. Remember that the threshold for soybean loopers (and all defoliating pests) is 15% defoliation throughout the canopy. Loopers generally defoliate from the bottom of the canopy up so peel back those plants when you scout.
Although pyrethroids will knock loopers back initially, they will often resurge because they are tolerant to these chemicals and because natural enemies are removed. My top choices for soybean looper are Belt, Prevathon and Steward. There are premix products that will also work, such as Besiege, but these should only be used if you need the non-worm portion of the premix (such as stink bugs or kudzu bugs at threshold). Remember that you want to preserve natural enemies if possible. Tracer/Blackhawk and Intrepid are also good effective chemicals for loopers.
Dominic Reisig, North Carolina State University Extension Entomologist