Patchy emergence could be cutworms

From Canola Council of Canada

Seeding is the top priority right now, but take time everyday to scout emerged canola fields. Cutworms have been observed in some areas already and can wipe out huge patches of canola if they’re left unchecked for too long.

May 20, 2011

Cutworms are in a cycle of abundance on the Prairies, and canola damage has already been noted in parts of central Alberta. Growers across the Prairies need to check emerged canola crops for bare patches, holes or notches in foliage, and clipped plants — telltale signs of cutworm feeding.

If 25% to 30% of the stand is reduced, a spray may be necessary to stop further damage.

How to scout: Start with an above-ground scout of the canola stand. Look for signs of cutworm feeding. If you see bare patches, holes or notches in leaves, and clipped stems, then start digging. Cutworms come out at night to feed then go back underground during the day. In moist soils, cutworms will stay close to the surface. In dry soils, they may go down 8-10 cm (up to 4″).

Dig up one square foot of surface area to a depth of 10 cm in several spots near surviving plants and put that soil into a basin. Loosen the soil and shake it up.

What to look for: Cutworms have a large head capsule, 4 sets of abdominal prolegs, and the tendency to curl up when disturbed. Scouting is important to make sure cutworms are present and to make sure they are the likely cause of crop damage. Look for green material in the gut of the larvae to confirm they are actively feeding on the canola plants.

At least four cutworm species damage canola: dingy, redbacked, pale western and army. Each species has its own markings and colours, but all have the general cutworm features.

• Dingy are grey with light markings down the back that look like tire tracks or a series of “V”s. They are present across the Prairies, start feeding early in the season, and tend to feed on above-ground foliage. They often leave bare patches in the field.
• Redbacked have two reddish stripes down the back. They are more common in Manitoba and eastern Saskatchewan. Younger ones feed on foliage. Older ones will cut stems.
• Pale western are light colored with a dark brown head. They are more common in Alberta and western Saskatchewan. They tend to feed underground, making them harder to control.
• Army are yellowish with dark stripes. They tend to be more common in Alberta and eastern Saskatchewan. They feed on foliage.

Wireworms are another below-ground feeder and can cause similar bald patches to appear in canola fields. Wireworms are straw-colored, do not have a prominent head and do not curl up when disturbed. No products are registered (or effective) for wireworm control in canola. If wireworms are the culprit, put away the sprayer and make note of areas or fields where the damage was higher. Remember these areas when planning crops and seed treatments for next year. Canola may not be the best crop for fields with high wireworm numbers.

Control strategies: If 25% to 30% of plants in the whole field or, more likely, in a smaller area within the field are lost and cutworms are the leading suspect, a foliar insecticide spray can manage the threat. Many products are registered for cutworms in canola. Click your province for your guide to crop protection:  Alberta Saskatchewan Manitoba

• Spray as close to nightfall as possible. Since not all cutworms will surface on a single night, it may take several days before full effect of the insecticide is achieved.
• Use high water volumes to get good plant coverage. Cutworms need to ingest the insecticide, so the more surface area covered, the more likely that cutworms will take in the insecticide.
• Try patch spraying. If stand reduction is concentrated in small areas, a targeted application of a sprayer width or two around that area can be a lower cost and effective way to manage the pest compared to spraying a whole field. Scout the surrounding area to see how far beyond the patch to spray. Keep scouting after spraying (when it is safe to re-enter the field) to make sure you have the damage contained.