Soybean Looper Thresholds and Insecticide Recommendation
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Soybean loopers have already shown up in coastal counties in higher numbers than usual. As this generation cycles through, we are seeing the next generation showing up in full force as we slide into September. Almost without exception, the fields where I have seen loopers at high levels have been behind pyrethroid or organophosphate sprays (bifenthrin and Orthene being the most common examples). Be sure to watch these fields carefully.
To properly treat loopers you must 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. I get worried when there is more than one looper per swoosh of the sweep net.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 (see graphs below for how loopers can be flared with bifenthrin and Besiege). This year, as in previous years, the most consistently effective insecticide we have tested is Intrepid Edge. Be sure to use 5 or more ounces.
Loopers numbers were clearly flared in certain plots with pyrethroids (Brigade or Besiege). While this isn’t always the case (numbers were lower in other plots), broad spectrum insecticides more often than not will flare loopers.