Loopers that we saw in late July and early August never went away, but more adults are picking up in our pheromone trap and small larvae are showing up in soybeans from this new batch. Here are two keys to managing late-season loopers:
1) Scout and use thresholds. Thresholds are easy post-bloom, with 15% defoliation throughout the canopy needed for a spray. Loopers eat only foliage and do not eat pods or seeds. Keep in mind that beans are more tolerant to defoliation as they mature, with the R3-R5 stages being the most sensitive and R6 much less so (you can probably can tolerate over 50 or 60% defoliation at this stage). R7 beans are safe from yield loss to defoliators like loopers. Loopers eat the most during the last three days of their life. So don’t wait to treat a borderline threshold field when loopers are small.
2) Insecticide choice, rate, and coverage is key to efficacy. Loopers start feeding on the bottom of the plant and move up. You must push insecticide down into the canopy. Pyrethroids kill natural enemies. Since loopers are tolerant of pyrethroids, when used alone, they can flare loopers after treatment. So a worm specific material must be used to manage them.
Examples include Belt, Blackhawk, Prevathon, Intrepid Edge, and Steward. Some pre-mixed products contain worm specific materials and a pyrethroid, such as Consero and Besiege. These are good choices if you need to pick up other things like stink bugs or bean leaf beetle. See this article for special insecticide recommendations for the Blacklands only. Finally, check the label and be sure to use the highest labeled rate for the best results.