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Green cloverworm (Hypena scabra Fabricius) is one of several insects that feed on soybean leaves. Additional hosts of green cloverworm include alfalfa, clover, vetch, strawberry, and various other legume and weed species.1
Adults. Green cloverworm moths are dark brown to black with speckled wings and a wingspan of around 31.5 mm (approximately 1.25 inches) wide (Figure 1). Female moths are typically more brown and silver in coloring than male moths.2,3
Eggs. As temperatures warm in the spring, females will lay eggs on the undersides of leaves. Eggs are hemispherical in shape, light-green in color, and about 0.5 mm in diameter.2
Larvae. Larvae grow from pale yellow, 0.5 mm long catepillars (first instar) to light green, 30.5 mm (about 1.25 inches) long catepillars (sixth instar). They often have two white stripes that run the length of their body, and may move violently when touched. They can be confused with soybean loopers, but can be distinguished by having four sets of prolegs, three sets in the middle of their body and one pair at the end of their abdomen (Figure 2).2,3
Young larvae will feed on the underside of soybean leaves, leaving the leaf tissue above untouched. As the larvae mature, feeding will continue to include all interveinal leaf tissue, leaving a skeleton-like appearance. Damage is typically found on the upper half of the plant, and in severe cases, can lead to complete defoliation.3.4
To assess defoliation of a soybean crop, begin by selecting at least 20 to 25 plants that are randomly selected throughout the field. Green cloverworm prefers to feed on the upper half of the plant, so defoliation will likely be concentrated in the top. Percent defoliation should take the whole plant into consideration.3 To sample, take a minimum of 20 sweeps with a sweep net in 5 different locations of the field. Record any larvae that appear to be diseased or parasitized, and if any other leaf feeders, like bean leaf beetle, are present.4
Typically, the use of insecticides to control green cloverworm is not necessary because of several natural predators of green cloverworm. Parasitized green cloverworms may be cigar-shaped and look mummified. Diseased green cloverworms may be sluggish and light in color, or covered with powder with half of their body in the air.3
Insecticides are recommended if defoliation is 40% prior to bloom,15% during bloom and pod fill (R1-R4), and 35% after pod fill to beginning maturity (R5-R7). Treatment is not recommended once the crop reaches maturity (R8). Green cloverworm is one of many insects that feed on soybean leaves. Application decisions should be based on a complete analysis of insect populations and damage.3