Cutworms are a pest in many crops. Although they are most often found in canola, peas and lentils, they will also feed on cereals and other crops as well. The three main species found in Saskatchewan are the Redbacked, Dingy, Army and Pale Western cutworms. It is important to scout for them in May and June as they can be detrimental to plant stands.
Scouting and Identification
When scouting, look for bare patches in field, holes in leaves, wilted plants, or plants that have been chewed off nearthe soil surface such as in Figure 1. Pale Western and Redbacked cutworms mostly feed below ground, whereas Dingy and Army cutworms are predominantly above ground foliar feeders. Cutworms curl up when disturbed.
Figure 1. Cutworm, damaged plant and bare patch
When scouting, pay attention to hilltops and compacted areas, pea or lentil stubble, fields with high trash, weedy patches, or canola on canola stubble. Cutworms move quickly, so if you suspect them in an area of a field but are having trouble finding them, flag or spray paint the damaged area and see if it has moved past after 24 hours.
Important considerations when determining if you should spray include: insect size, level of infestation, crop stage, environmental conditions and existing plant stand. Foliar insecticides include Coragen, Lorsban, Matador, and Pounce. Available seed treatments include Lumiderm and Fortenza.
Table 1. Economic thresholds in various crops
Cutworms bury below ground during the heat of day and come out when the soil temperature drops, so they need to be sprayed late in the evening or overnight.
It is common to spot spray for cutworms (e.g. hilltops) although severe infestations may require spraying an entire field. An important method of cultural control is to maintain weed free fields in the fall as the moths are attracted to weedy fields (especially flowering) and will lay their eggs there which will then hatch in the spring.
Summary
Cutworms are a pest of many crops and can cause significant losses if not controlled. Use of insecticide maybe needed where infestations are severe. Consider a seed treatment for high risk fields.
Hana Ruf, PAg
Precision Agronomist
hana@croprecords.com