Problem type: Insect

Name of problem: Cutworms

Plant name(s): Field crops, vegetables, lawn, home garden plants

Symptoms / Characteristics:
Cutworms feed on the base of plants, cutting off the stems near the ground. Damage on grass plants may appear like sunken pocket marks and seedlings or other herbaceous plants may show signs of wilting. Short stems may be left or they may be cut off below the soil line. Holes and notches may be chewed in leaves, as some cutworms will climb the plant.

Their life cycle consists of an egg, larva, pupa and adult stage. Generally there is one generation per year. Adult moths can lay hundreds of eggs on host plants. They can overwinter in any stage but eggs are most commonly laid in late summer and overwinter in this stage. The eggs then begin to hatch around May and larval feeding begins by June. This spring generation of larvae is the most damaging as plants are just starting to grow. Larvae feed for a couple of months growing from 3-5 cm long. Cutworm larvae usually have a variegated appearance being dull in color with reddish, brown or pale stripes along the entire length of the body. Cutworms are nocturnal, feeding at night and hiding during the day making them hard to detect. Cutworm larvae are known for their C-shaped, curled position, especially when disturbed. Larvae tunnel in the soil to pupate, and emerge shortly as adult moths in August.

On the prairies, strawberry cutworms may be of particular concern. The larvae of strawberry cutworms are whitish-yellow with a pair of thick, brownish-purple stripes running lengthwise along the back. They can reach a mature length of approximately 30 mm. Immature larvae begin feeding on leaf and fruit stems. Once mature, they begin boring into the crown of the plant. This activity typically results in plant death. Wilting symptoms associated with strawberry cutworm feeding are often confused with winterkill. Damage is most severe in older, more mature plantings where larger populations of cutworms have become established.


Control / Preventions:
Inspect plants starting in May through to July. Look for the larvae just below the soil line, down to about 2 inches. Look for signs of feeding on stems, petioles and leaves. Plants may appear wilted and will pull out of the ground quite easily. Adult moths are nocturnal and attracted to light. Light traps can be used to reduce adult populations. Small populations of larvae can be controlled by digging them up and removing them from the soil. A single larvae can destroy many seedlings in one night, so only a few cutworms per square meter can destroy thousands of seedlings in a week. In instances of high population levels, insecticides are available. An application of a commercially available cutworm dust can be applied. Spraying with insecticides are most effective against young larvae. These should be applied in the late day or evening when cutworms are most active. Spot applications should be made where damage is confined to one area.

Proper cultural practices can help to prevent cutworm infestations. Removing weeds and mowing grass low in the fall can prevent egg-laying sites for the adult females. Cutworms can feed on vegetables and fruit, so keeping branches from touching the ground and keeping the ground mowed under the plant will reduce the chance of invasion. Remove all debris, mulch and till the soil 4 inches deep in the fall and spring as they overwinter in the soil. To protect individual plants, placing containers into the soil about 2 inches deep around the base of the plant can prevent larval feeding. Inspecting plants early and catching cutworm larvae while they are young and few will provide the most effective control.


Photos:
cutworms


Relevant web sites:
www.gov.mb.ca/agriculture/crops/insects/fad06s00.html
www.pfc.cfs.nrcan.gc.ca/diseases/nursery/pests/cutworms_e.html