Grasshopper damage from outbreak due to grassy residue: Sometimes, soybean is not the primary host for an insect. In this case grasshopper numbers were increased greatly by the presence of the weed, yellow foxtail, in this field the previous cropping season where females laid their eggs. The following spring the yellow foxtail was killed off with an herbicide, leaving soybean as the only food source for the grasshopper nymphs. The grasshoppers were thus driven off of the yellow foxtail and onto soybean by the weed-management practice in this case. The yellow areas of the field are the dead stems of yellow foxtail showing through the defoliated soybean plants. (Photos Marlin E. Rice)
Grassoppers and locusts have a long, and notorious history in Iowa (Drake and Tauber 1945) and, fortunately, Iowa growers no longer experience plagues of grasshoppers as in the late 1800s. However, localized outbreaks of differential and redlegged grasshoppers can still occur that cause damage to both soybean and corn on a small scale (Rice 2001). Defoliation is usually most severe during late summer when adult grasshoppers do most of their feeding, but significant defoliation can occur on seedling soybeans during the spring if grasshopper populations are large.
Grasshopper and grasshopper damage to soybean pods: A redlegged grasshopper, Melanoplus femurrubrum, and an injured soybean pod. In high populations grasshoppers can cause considerable injury to soybean pods. They will chew through the pod wall to feed on the mature soybean seed inside. (Photo Marlin E. Rice)
When late summer grasshopper damage does occur, it usually is related to drought conditions and is frequently, but not always, restricted to field edges. However, some management practices, such as allowing weedy grasses to proliferate throughout a field where females will lay their eggs during late summer, can aggravate grasshopper problems in a field the following year. (Add photo from Loess Hills grasshopper damage as example).
Differential and redlegged grasshoppers will feed on a wide range of plants including soybeans, corn and alfalfa, but they prefer grasses (USDA-APHIS 1989). As soybeans start to mature during late summer, grasshoppers will feed on soybean pods by chewing through the pod wall and eating the developing seed. This feeding injury may be distinguished from that caused by bean leaf beetles, which only scrape the outer pod tissue and do not penetrate the pod wall to feed on the developing seed.
Grasshopper damage to soybean: The bare areas in this field (both foreground and background) were caused by grasshopper nymphs hatching in the field and feeding on seedling soybeans [top]. Grasshopper nymphs may completely strip seedling soybeans of all leaf tissue as shown on several plants [lower left]. They will eat most leaf tissue except for the tougher leaf veins [lower right]. (Photos Marlin E. Rice)
Grasshopper injury to soybean: Grasshoppers will eat most leaf tissue except for the tougher leaf veins. (Photo Marlin E. Rice)
Soybean pod damage from grasshoppers: Grasshopper damage soybeans by chewing through the pod and biting into the developing seed. (Photo Marlin E. Rice)
Grasshopper cornstalk damage: Large populations of grasshoppers also can defoliate corn. (Photo Marlin E. Rice)