Manitoba Agriculture, Food and Rural Initiatives
Cutworms I
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Cutworms can be a serious problem in many field crops.
There are many different species involved but two of the most common ones are the
redbacked cutworm and the army cutworm.
Host Crops
The redbacked cutworm feeds on practically all field crops, vegetables, and home garden plants. It is best known for its feeding on cereals, flax, sugar beets, canola and mustard.
The army cutworm feeds on the foliage of wheat, oats, barley, mustard, flax, alfalfa, sweetclover, field peas, cabbage, sugar beets, corn, oats, potatoes, various weeds (notably stinkweed) and grasses. Almost any crop, present during the early spring, could be a potential host.
Biology
Cutworm larvae (Figure 1) have four sets of abdominal prolegs and curl up when disturbed. Red- backed cutworms are dull-gray to brown in colour and have a pink, red or reddish-brown top-stripe that extends the entire length of the body. The top-stripe is divided by a dark line and bordered by darker bands. The head is yellowish-brown. Army cutworms are pale greenish-gray to brown in colour. They have pale stripes down the back and a mottled pattern. They also have a lighter band along the sides.
Cutworm moths may lay several hundred eggs in or on the soil. After the eggs hatch, the larvae feed on the host plants. They moult several times, eventually reaching about five centimetres (two inches) in length. The larvae tunnel into the soil to form earthen cells where they pupate. The new moths emerge, exiting through the soil using the old larval tunnels. Some species overwinter as eggs (eg, the redbacked cutworm); others, as larvae or pupae. Still others do not overwinter in the Prairies but rather re-invade annually from the U.S., aided by southerly winds. Most of our pest species have only one generation per year.
| May | June | July | August | September |
| Overwintering eggs begin to hatch | Larval feeding begins | Larval feeding continues, pupation begins | New moths emerge, lay eggs | Eggs overwinter |
Scouting Techniques
Inspect the seedlings on at least a weekly basis, from mid-May to mid-June. Feeding by cutworms results in notched wilted, dead, or cut-off plants (weed or crop seedlings). Plants may be missing from rows and bare patches may appear in fields as a result of cutworm feeding. Often cutworms will be close to the cut of shriveled plants they have just damaged and can be found by digging around these plants. Cutworms will sometimes be most abundant in patches or a specific area of a field. A garden trowel and a soil sifter are useful tools for collecting cutworm larvae. Cutworms may be found down to about five centimetres (two inches) below the soil surface. The small, worm-like larvae curl up or attempt to hide in the debris. Pupae may also be collected in this way.
Economic Thresholds
Treatment is warranted when cutworm densities exceed 10/m2. Insecticides are available to control cutworms. Consult the Guide to Crop Protection for product information.
Control Tips
Best results occur if insecticide applications are made in the evening. Sometimes it is most economical to just treat infested patches and not entire fields.
Young cutworm larvae may be starved before spring seeding by allowing volunteer growth to reach three to five centimetres (1.2 to two inches), cultivating and then seeding 10 to 14 days later.
Many predaceous insects, parasites and birds prey upon cutworms and reduce their populations.
For further information, contact your GO representative.
