Green Cloverworm Identification in Soybean

Green cloverworm (GCW) can be found in most soybean growing regions of the United States. Alfalfa and soybean are their preferred legume crops for feeding; however, dry beans, clover, cow peas, and many common weeds are also hosts. Though common in soybean, economic damage is rarely seen.¹

Green cloverworms are often confused with looper caterpillars. The difference being GCW has four abdominal prolegs and loopers have three (Figure 1). In addition to the four abdominal prolegs, they have three legs near the head and have a narrow white strip on each side of their body (Figures 1 and 3). Another interesting GCW trait not found with other soybean caterpillars is the dramatic jumping action the larvae do if touched. 

The life cycle includes the pupal overwintering in leaf litter and crop debris. As temperatures warm in the spring, the adult moths emerge in two to three weeks, mate, and lay single eggs on the underside of the soybean leaves (Figure 2). The caterpillars emerge and feed for approximately four weeks. Young larvae skeletonize the leaf underside while older larvae eat the entire leaf except for the large leaf veins. Usually feeding occurs in the top third of the plant (Figure 3).

After this feeding period, they crawl to the ground, burrow under the liter, spin a cocoon, and pupate. There are usually two to three generations per year depending on the length of the growing season.

Assessing the economic damage to a soybean crop can be done by a two-step evaluation starting with a sweep net. Using the net, sweep at least five areas of the field, making twenty sweeps per area. The five areas should be considered a minimum. With more sweeps the population evaluation in the entire field becomes more accurate. Once the number of GCW have been counted per area, obtain an average per area across all the samples taken.

Control measures are not recommended if fewer than twelve to thirteen larvae per row foot are found. If the number exceeds this treatment threshold, then a determination of the percent defoliation of the plants should be made.¹ If plant defoliation reaches 40% in pre bloom stage, 20% during bloom and pod fill, or 35% from pod fill to harvest then treatment is warranted.³

Green cloverworm populations are usually kept in check by fungal diseases, viruses, parasites, and predators. Beneficial insects feed on GCW; therefore, proper assessment of economic thresholds are important before control measures are implemented because the beneficial insects can be killed too.

Channel Agronomist
Steven Troesser

Sources:

¹Johnson, D. 2001. Green cloverworm in Kentucky soybean. ENTFACT-142. University of Kentucky. https://entomology.ca.uky.edu/ef142/.

²Green cloverworm identification. CROPWATCH. University of Nebraska-Lincoln. https://cropwatch.unl.edu/insect/geencloverwormid

³Obermeyer, J. Green cloverworm. Hypena scabra Fabricius. Integrated Pest Management. IPM Field Crops. Purdue University. https://extension.entm.purdue.edu/fieldcropsipm/insects/green-cloverworm.php#:~:text=Green

Green cloverworm. Soybean Pests. Soybean Research & Information Network. https://soybeanresearchinfo.com/soybean-pest/green-cloverworm/.

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