Alabama Cooperative Extension System entomologists have been watching soybean looper numbers rise for several weeks. The major outbreak entomologists warned against earlier in the summer is happening in soybean fields in south and central Alabama.
Soybean loopers are also increasing in number in many north Alabama soybean fields. These are the key species triggering treatments during the third week of August in some fields in the Tennessee Valley for the complex of foliage feeding and pod feeding worms infesting double-cropped soybeans. The most recent year in which the soybean looper was a serious pest of north Alabama soybeans was 2012 when treatments were initiated the first week of September.
Extension researchers have pest traps scattered at locations throughout the state. High soybean looper trap counts in July gave entomologists reason to believe the looper numbers would be higher than average in early August.
Extension entomologists Dr. Ron Smith and Dr. Tim Reed saw moth counts grow rapidly along the Gulf Coast in June and July. There were high counts in some Elmore County traps as well.
Scouting for Soybean Loopers
Reed and Smith are encouraging farmers to diligently scout soybean fields.
“The occurrence of soybean loopers is widespread in soybean fields in south and central Alabama at this time,” Smith said. “With widespread pest pressure, if a grower does not have a commercial scout, it is important to actively look for soybean loopers themselves.”
Farmers in the Gulf Coast area of Alabama began adding insecticides to their fungicide sprays for some fields during the first half of August to slow the increase in soybean looper numbers.
Herbicide Resistance Info
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Soybean looper larvae feed primarily on foliage. They will normally start feeding in the lower half of the plant canopy and move upward over time. Reed said scouts should try get their sweep nets into the lower half of the canopy if possible to get a more accurate estimate of soybean looper numbers. Soybean loopers are more difficult to dislodge from soybeans than other foliage feeding caterpillars.
“Early on, farmers will see leaves with a window pane effect,” Reed said. “The very small soybean looper larvae eat only the green portion of the leaf leaving behind the transparent cuticle layer. As larvae mature, they become more aggressive feeders and once soybean loopers begin feeding on the upper canopy, they can soon consume more than 50 percent of the foliage when numbers are high.”
Soybean Looper Control
Smith said soybean loopers are the most expensive pest to control. While there is more than one option, there are a limited number of control options available for soybean loopers–ranging from less than $10 per acre to nearly $20 per acre. Intrepid, Intrepid Edge, Belt, Besiege, Prevathon and Steward are the only four products available to farmers for soybean looper control.