Field Guide    Pest Management  Western Bean Cutworm

Family: Noctuidae

About Western Bean Cutworm

Although it’s similarly named, the Western Bean Cutworm cannot be considered a true cutworm since it feeds on the reproductive parts of corn ears and bean pods, rather than the stems of plants. The species was first discovered in the Great Plains region but migrated eastward into Ontario in 2008.

Western Bean Cutworm Reproduction and Life Cycle

Only one generation of Western Bean Cutworm occurs each year with adults emerging from the soil in mid July. Female moths will mate and lay eggs during July and August, preferring cornfields that are late in whorl stage (near but not past pollination). The females lay eggs in masses of 5-200, averaging 50 eggs per session. These eggs are attached to the upper surface of corn leaves, close to the tassel. Once hatched, the larvae feed on mature ears of corn and by late August, they burrow into the soil where they lie dormant until springtime when they pupate.

Western Bean Cutworms Identification and Habitat

Identification

These moths are typically greyish-brown in color and at full maturity have a wingspan of 1-1/2”. Their primary identifier is the white stripe at the front of the forewing, immediately followed by two cream-colored shapes: a circular spot halfway along the length of the forewing and a crescent moon shaped mark along the same line approximately 2/3 of the way to the wingtip.

Habitat

The Western Bean Cutworm is typically found on farms that grow corn or dry beans as a crop. The female will lay eggs on the upper leaf surfaces on the upper part of the plant. Areas with sandier soils allow for larvae to penetrate deeper into the soil and increase chances of their survival until spring.

Western Bean Cutworm Management and Control Methods

Culture Control

This pest is a challenge for pest managers but there are a few effective alternatives to chemical control. Pheromone traps can be used to target scouting efforts but this method does not determine when the best time to spray. As moth flight begins in late June, pheromone traps should be in place by mid-June and should be checked weekly during the late afternoon and evening. Once multiple moths are caught and the frequency increases, scouting can begin. It is recommended to scout 20 plants in five areas of the field from early July to end of August when the crop is in the pre-tassel to full tassel stages. This will likely be difficult as infestations are very patchy and oviposition occurs over several weeks. As well, the treatment window is limited to the period surrounding the egg hatch because larvae will be difficult to find once they enter the plant.

Chemical Control

If eight percent of the plants have egg masses or small larvae then chemical control should prove to be economical. Insecticides can be effective in infested crops but it is important to observe egg hatch to know when the larvae will be active. Spraying too early or too late will not prevent the plants from crop damage. Insecticide application should be timed so that 80-90% of tassels have emerged and if tassels have already emerged than applications should occur when 70-90% of eggs have hatched. It is important to note that the larvae must encounter the insecticide before entering the ear otherwise the applications are not as likely to contact larvae and they will become difficult to control.

Sources

http://fieldcropnews.com/wp-content/uploads/2017/05/WBC-2017-Dry-Bean-Infosheet-2.pdf

https://extension.entm.purdue.edu/ fieldcropsipm/insects/western-bean-cutworm.php