View Mike's presentation from Corn Congress
Most NY corn producers are familiar with the damage that cutworms can cause to seedling corn plants. We are most familiar with the black cutworm (BC). Most farmers have done battle with this beast at some point over the years. This moth (the adult of BC) does not overwinter here in NY. It flies north each spring to lay eggs on early green vegetation and stubble in fields. The BC is best known for its ability to cut down young corn plants by chewing through the stem at ground level. It is strictly a stalk and leaf feeder and plants are safe from damage once they reach the 6 leaf stage.
A Different Kind of Cutworm: Over the past couple of seasons you may have read a magazine or web article about a cutworm that is causing significant damage to corn grain in the Midwest. This new pest is the Western Bean Cutworm (WBC).
The WBC has been a recognized pest in Colorado, Nebraska, and Kansa since the late 50’s. However, starting in 2000, WBC populations really started to multiply in Iowa and move across the whole state. In 2004, this pest was first found damaging corn in NW Illinois and by 2006 it had mowed across WI, IL, IN and into MI and western Ohio. The adult moths are obviously good fliers and populations are moving rapidly eastward.
Biology: WBC overwinters in the soil as mature larvae inside a protective earthen cocoon. As soil temperature increases, the larvae pupate and emerge in early summer. Female moths lay their eggs on the upper third of the corn plant on the top side of the leaves. Eggs are white and usually laid in clumps of 50. Egg color will change from white to purple to black as they near hatching, which takes five to seven days.
Larval Description: The young larvae are dark brown with faint cross hatched markings on their back. As the larvae develop, they become light tan to pink in color and the cross hatch markings on their backs become more distinct. Third instar and older larvae also can be differentiated from other feeding caterpillars by three characteristic dark brown stripes immediately behind the head.
Feeding Habits and Damage: Newly hatched western bean cutworms move to one of two places on the corn plant depending on the stage of development of the corn. If corn has not tasseled, larvae feed on pollen in the developing tassel within the flag leaf. If corn has tasseled, larvae feed on silk in the ear.
Larvae feed for about 35 days and develop through five stages (instars) on the plant. Young larvae are quite mobile and may travel to adjacent plants. Second and third instar larvae continue to feed on the silks and begin feeding on the tips of the developing ears. Fourth instar larvae feed primarily on the ear tip. While one larva per ear rarely causes an economic loss, recent research has shown that a field average of one larva per plant at dent stage can reduce yield by 3.7 bu/acre. Western bean cutworm larvae are not cannibalistic, like corn earworms, which may result in multiple larvae per ear. Infestations averaging several larvae per ear can result in the reduction of grain yield by as much as 30 to 40 percent. Corn ears infested with more than twenty larvae have been recorded.
Management and/or Control: Western bean cutworm management has traditionally been through field scouting and application of insecticides. Much like corn earworms, WBC needs to be controlled prior to their movement into the ear. Natural enemies such as ladybird larvae and adults, nabids and spiders take their share of early stage worms. More recently, Bt hybrids containing the Herculex technology have been used as a management tool.
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