Loopers are a common defoliating caterpillar found in soybeans. They do not feed on pods. Both soybean looper and cabbage looper may be present. However, in Tennessee, economically damaging infestations are uncommon until mid-August and September, and these infestations are often composed mostly of the soybean looper. Larvae of both species are light green and have two pairs of prolegs (excluding the pair on the last abdominal segment). The caterpillars move with an inch-worm or looping fashion when crawling. The body is thickest at the rear and tapers to the head, reaching a length of about 1.3 inches. Populations are often held in check by beneficial insects and diseases. For more information visit the Soybean Insects Loopers Fact Sheet (W199).
In an average sized field, take 25 sweeps with a sweep net and count the number and kinds of larvae that are found at 4 locations. Increase the number of sampling sites in large fields (> 50 acres). Also, visually estimate percent defoliation at each sampling point. It is important to document what other pests are present and may also be contributing to defoliation.
Treat at 30% defoliation until bloom (R1), 20% from bloom to full seed (R1-R6), and 30% after R6 to R6 plus 7-10 days. Alternatively, an insecticide application can be made when infestations average 19 loopers per 25 sweeps, but it is generally suggested not to count larvae less than ½-inch long because small larvae do not cause much defoliation and natural mortality is often high.
|Insecticide (Trade Names) for LOOPERS||Lb Active Ingredient per Acre||Amount Formulation per Acre||Performance Rating Soybean/ Cabbage|
|chlorantraniliprole (Prevathon 0.43 SC)||0.047 - 0.067||14 - 20 oz||8/9|
|chlorantraniliprole, λ-cyhalothrin (Besiege)||See label||10 oz||8/9|
|indoxacarb (Steward 1.25)||0.055 - 0.11||5.6 - 11.3 oz||8/9|
|methoxyfenozide (Intrepid 2)||0.063 - 0.125||4 - 8 oz||8/9|
|spinetoram (Radiant SC 1)||0.016 - 0.031||2 - 4 oz||8/9|
|spinetoram, methoxyfenozide (Intrepid Edge)||See label||4 - 6.4 oz||9/9|
|spinosad (Blackhawk 36% WDG)||0.034 - 0.05||1.1 - 2.2 oz||8/9|
- Late maturing varieties are much more likely to be infested with soybean loopers.
- Soybean looper is more difficult to control with insecticides than the cabbage looper. Although many pyrethroid insecticides are labeled for soybean looper control, they are not recommended because resistance is well documented. Indeed, use of pyrethroid insecticides can worsen infestations of soybean looper.
- Soybean loopers often, but not always, have black true legs (those behind the head) and/or black spots on the bodies.
- Treatable infestations of loopers prior to August, although uncommon, are likely to be cabbage looper and can often be controlled with pyrethroid or other insecticides. It is generally best to assume late season infestations are composed mostly of soybean looper and to use the recommended insecticides listed above.
- Do not confuse loopers (2 pairs of prolegs) with green cloverworm (3 pairs), which are easier to control with insecticides.
- For more information see https://extension.tennessee.edu/publications/Documents/W199.pdf.