Cutworms & Wireworms
As soil temperatures are heating up and crops are beginning to emerge across Manitoba, it’s time to start scouting for cutworms and wireworms. Agronomists in north central North Dakota have been finding wireworms feeding on newly planted wheat seed. Cutworm damage has also been reported in central MB as well as north central ND.
Wireworm larvae are slender, hard and smooth worms that can vary in length from 1.5-2 inches in length. They tend to be either white, yellow or brown in color and have three small pairs of legs behind the head. Moist soil conditions are favorable for larval movement in the soil, and as the soil heats up, wireworms will move to the surface and begin feeding on seeds and plant tissue.
Wireworm damage can reduce plant stand and vigour, ultimately resulting in yield loss. Reports from North Dakota indicate that wireworm activity has been increasing in recent years, especially in reduced-till fields.
Image courtesy of Manitoba Agriculture
- Know the history of wireworm population levels in your fields. Larvae can survive for 3-5 years in the soil, so if populations are high, that field will remain at risk for several years.
- Chemical control options include a neonicotinoid seed treatment or an in-furrow pyrethroid insecticide. It should be noted that neither of these chemical control options provide high ‘kill’ levels in the field. In a study of sunflower, no additional benefit was seen when both a seed treatment and an in-furrow insecticide were used.
- Control grassy weeds to prevent egg laying by wireworms.
- Increase seeding rate to account for wireworm stand loss.
The best time to scout for cutworms is during the evening, as they hide underneath soil and surface residue during the day, and feed at night. Small grains tend to be less affected by cutworm damage, as they can compensate with increased tillering. Cutworms will often move down the row as they feed on plants and can do significant damage during the early growth stages (seedling- 4-6 leaf stage) of the crop. In small grain crops, threshold levels are between 4-5 larvae per square foot.
- Insecticides are available to control cutworms. See the Guide to Field Crop Protection for product options. Efficacy tends to increase if applied in the evening.
- Cutworms have many natural enemies (insects, parasites, birds) that naturally reduce populations.
Article written by MWBGA Agronomy Extension Specialist, Mallorie Lewarne
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