The species Plathypena scabra is widely known as the green clover worm, which commonly infests dry bean crops. In general, green clover worm infestation is not necessarily a major threat, especially if a given crop is able to compensate for the foliage damage; however, with high infestations occurring in a short time, severe crop losses can occur, thus requiring an insecticide treatment.
Adults are dark brown or black moths with spotted wings. The larvae are pale green, approximately 2.5 cm in length and have two white longitudinal stripes running along the length of the back.
Young larvae can ‘skeletonize’ the underside of the leaf, whereas older larvae eat all of the leaf except for large veins. Generally, they first feed on the top third of the plant and continue descending as they develop in the crop. This can give the plants a damaged appearance long before economic damage is sustained. When scouting, a common practice used is a shake cloth placed between the rows to sample the level of infestation.
At several locations in the field, place the shake cloth on the ground and shake the plants over the cloth. Shake two feet of row on each side of the cloth. Once you have visited several locations in the crop, average the numbers you collected at each site. An average of several sites will provide you with a good understanding of the level of infestation. A nominal (empirical) threshold has been determined, and according to the experience of farmers and extension professionals, more than 12 worms per row-foot is close to the approximate economic threshold to make decisions on applications.