Cutworms are a destructive pest insect of a wide variety of plant material. Many home gardeners have encountered them in the vegetable garden, where they chew through the stems of their seedlings, cutting them off near the soil line. There are hundreds of species of cutworms and appearances can vary, as well as habitat, food preferences and life cycle. There are however several general characteristics, and common methods of controlling and managing this pest.

Meet The Pest

Adults: moths are commonly variations of brown, black and grey with unique patterning on their wings which helps to identify the species. Forewings are often darker than the hindwings and may be a different colour all together, such as the Yellow Underwing moth with its bright yellow-orange hind wings. Size wise their bodies are about 2.5cm in length with a wingspan of about 3-4 cm, although they can be double that size, again like the Large Yellow Underwing moth. They have hairy bodies and fly at night. Adults of a few species migrate south during the winter and return in the spring to lay their eggs such as the black cutworm and the variegated cutworm.

Larvae: are short, fat, mostly hairless, caterpillars measuring between 2.5-5cm (1-2″) in length. Colouring can vary appearing brownish, greyish, blackish, greenish, pinkish or yellowish. The colouring is usually dull although some are brighter. They may be 2 toned, variegated, and usually have distinctive markings like dots, stripes or dashes that help to identify the species. They are nocturnal, living in the top 5 cm of the soil or under debris during the day and come out to feed at night. They feed on a wide variety of plant material with each species having its preferred hosts. They commonly feed just above the soil line, by chewing through stems until they are cut right off. Some species, like black cutworms and turnip moth caterpillars also feed on roots, and a few species such as variegated and dingy cutworms are known as “climbing” cutworms and will feed on leaves, flowers and fruit, higher up on the plant. When disturbed, they curl up into a “C” shape. The pest may overwinter as larvae, pupae, eggs or the adult moths may migrate south to warmer zones for the winter.

Pupae: are varying shades of brown measuring about 2cm (3/4′) in length and found in the soil.

Eggs: are laid in clusters on dead plant material, on or near low-growing plants, commonly weeds, or on dry soil. Egg colour varies according to species but may be white, brown, black or yellowish. The eggs commonly overwinter and begin hatching in spring but a couple of species like the Black cutworm and the Variegated Cutworm, lay their eggs in the spring. They take about 4-10 days to hatch, depending on climate. In Canada there is usually just one generation per year, but Ontario can see two generations of some species, and warmer climates may see three or four generations.

Management and Control

Monitoring:

• Regularly examine plants for damage, especially in spring. If you find a plant that has been cut off near soil level dig down in the soil a couple of inches in search of culprit. In the ornamental garden monitor for chewed leaves and damaged buds and again shallowly dig around in the soil to see if you can find the cutworm(s).
• Monitor for the adults and prevent egg laying.

Cultural practices:

• Control weeds, many of which attract cutworms.
• Remove plant debris, as cutworms not only like to hide under garden debris the adults also often lay their eggs there.
• Till the soil in early spring and again in late fall to kill or expose them.

Physical control:

• Hand picking the caterpillars at dark, with a flashlight, when they are actively feeding.
• Install Protective barriers
  1. Place protective collars around transplants and young seedlings. Tin cans with both ends open work well as do the cardboard toilet paper or paper towel rolls. Plastic collars can also be used. Insert them about 5cm (2″) into the soil leaving 5cm-8cm (2″-3″) above the soil.
  2. Tie transplants and young seedlings to a short stake. This prevents the caterpillar from completely encircling the stem.
  3. Raised beds with floating row covers over them will help to keep caterpillars away as long as there are no eggs or pupae in the soil. The floating row covers are also useful when the adult moths are flying, to prevent them from laying their eggs in your garden.

Natural predators:

Help to attract natural predators of cutworms such as: toads, ground beetles, rove beetles, spiders and parasitic wasps.

Chemical free sprays

• Bacillus thuringiensis (Bt) sprayed at the caterpillar stage is quite effective, especially for species that feed on leaves and buds of ornamental plants. Spray in the evening, closer to the time they will be actively feeding.

Cutworm Species Commonly Found in Canada Include:

• Large Yellow Underwing aka. Winter Cutworm (Noctua pronuba); caterpillar larvae are greenish or brownish with two rows of black dashes that run down their back. They are very cold tolerant and will even feed during the winter, on milder days. The larvae actively feed from August to early spring. They pupate between May and July. The adults begin emerging in July and are in flight until September, when eggs are laid. The adult moths are quite attractive with bright yellow-orange hind wings that have a blackish band running across them, near the tip of the wing. The forewings range from light brown to dark brown with a black dot on the edge of each wing and another kidney shaped spot, called a reniform spot, further up the wing. Their wingspan is about 5-6 cm. Their bodies are similarly light brown to dark brown and are hairy. The larvae feed near ground level and can also be found higher up on the plant feeding on the leaves and buds of a wide variety of vegetables, ornamentals, weeds, grasses and hay. Photos

• Black Cutworm (Agrotis ipsilon) larvae caterpillars are fairly uniformly grey to black in colour, with a pale streak that runs down it’s back. Distinguishing markings include tiny black dots, called tubercles, that appear on each body segment, consisting of 2 larger dots and 2 smaller dots. Their skin appears greasy and highly textured. At maturity the larvae are about 4-5 cm (1 1/2″- 2″) in length. The young larvae feed on a large variety of weeds then moves into the soil by day and feed on most vegetable plants by night, cutting them off near ground level; they also feed on the roots. The adult moths are brownish to greyish with distinctive dark markings on their forewings, including a dagger-like marking towards the bottom of each wing. Their hind wings are generally lighter than the forewings. They have a wingspan of about 4-5 cm (1 1/2″- 2″). In the fall the adults fly south to over-winter then return to their northern homes in early spring to lay eggs, usually on weeds. There are 2 generation per year in Ontario but in warmer zones there are 3 or more. This is a common and highly destructive pest of vegetable gardens.
• Pale Western Cutworm (Agrotis orthogonia), is a common pest of the Prairies. The larvae are a pale yellowish colour at the beginning, with dark heads but they gradually turn a pale, brown or pale grey colour, with no distinctive markings and measure about 4 cm at maturity. They feed on herbaceous plants, grasses and occasionally winter wheat and small grains. The larvae start becoming active typically in late winter, early spring, when the soil surface reaches about 21 C (70 F) (Agrobase Canada, (n.d)). The adults are pale greyish or light brown and white, with darker markings, including a kidney shaped spot on the forewings. Hindwings are usually lighter than forewings and have a darker band running along the tip. The under surface of the wings are uniquely, white. Their body length is about 19 mm (3/4″) with a wingspan of about 35 mm (1 3/8″). Moths are in flight from late August until early October.
• Variegated Cutworm (Pedridroma saucia) along with Dingy Cutworms are unique in that they do not cut the plant stems down near soil level like the other species. Instead, this species climbs the plants at night and feeds on the leaves, fruits and flowers, leaving irregular shape holes behind. For this reason, they are known as “Climbing Cutworms”. Ornamental plants such as hostas and petunias, are particularly prone to their damage, as are vegetables, fruit trees and grapes. The larvae’s colouring can be quite variable with variegated shades of grey, black, brown, white and/or gold. They usually appear darker on the upper surface (backs) and creamy coloured on the lower surface (bellies). Down their back and sides, they have some unique markings including a row of yellowish dots down their back, and a narrow, orangish stripe that runs down their sides. At maturity they measure 4-5 cm (1 1/2″ to 2″) in length. This species tends to feed more in groups, rather than solitary. The adult moths often called Pearly Underwing, have grayish brown forewings with 3 distinct marking that help to identify the species: a pale oval marking with a kidney-shaped marking below it (when wings are closed) and 7 small dark marks running along the edge of the forewing. The hindwings are white with brown veins. Bodies are brown and hairy. There are two generations per season in Ontario with some warmer regions seeing up to 4 generations. The moths fly south to over-winter and return sometime in spring (later than other species) to lay their eggs on grasses and weeds, second generation in Ontario is late July to August. Photos
• Dingy Cutworm (Feltia jaculifera) like the Variegated Cutworm above are known as “Climbing Cutworms. They feed on the leaves, fruits and flowers, leaving irregular shaped holes behind. The larvae caterpillars are quite a dingy looking grey/brown colour with a band that runs down the length of the back, with a thin light coloured line running down the middle of the band. Also, within the band there is a “V” shaped marking in each body segment, along with 4 black dots in the 4 corners. At maturity they measure about 2.5 to 3 cm (1 to 1 1/4″). The larvae overwinter and are already a good size when they start feeding in early spring. The adult moth’s forewing is a dark gray/brown colour with attractive markings that almost look like stain glass windows, in a collage of browns. One of the distinctive marks is a white edged, triangle shape with a wavy line running down it; one side is baize, the other side is dark brown and at the bottom of the triangle is a cashew looking shape. The hind wing is lighter in colour, slightly darker towards the tips. Both sets of wings have a fringe of hairs along the bottom. The thorax is hairy (the area below the head) with a “W” marking on the upper surface. They have a wingspan of about 3 to 4 cm in length. The adults lay their eggs in the fall in composite flowers like asters, sunflowers, ragweed, goldenrod or others. Photos
• Black Army Cutworm (Actebia fennica) feeds in groups unlike most of the other species and can reach epidemic proportions if conditions are right. In Canada outbreaks have mostly occurred in B.C. to young tree seedlings of burned sites especially conifer seedlings like western larch and to low-bush blueberry crops in Newfoundland; but they occur elsewhere in Canada especially wooded areas. The larvae caterpillars start off velvety black with faint white striping and as they mature their colour becomes brown/black with a pair of creamy coloured lines on each of their sides running down the length. At maturity they measure about 4cm (1 1/2″) in length. The adults are blackish brown in colour with narrow forewings that have 2 distinct markings, a pale oval marking with a cashew-shaped marking below it (when wings are closed); male forewings also have a yellow/brown hind margin. The hind wings are creamy coloured with dark veins. Both forewings and hind wings have fringed borders along the bottom. Wingspan is about 4cm (1 1/2″). There is one generation per year and the pest overwinters in the larvae stage.
• Glassy Cutworm (Apamea devastator) is a North American native pest of grasses. The caterpillar larvae are greenish-white or greyish white in colour with a semi-translucent glassy appearance and a reddish/brown head. There are no prominent markings. At maturity they measure 3.5-4 cm in length. The larvae feed on the roots of grasses from Sept. through to April, when the temperatures are mild enough. The adults fly from June through August laying their eggs on the soil surface of primarily established grasses. The adult moths are grayish brown with several dark markings on their forewings and a wingspan of about 3.5-4 cm. Photos
• Bronze Cutworm (Nephelodes mimian) is another native cutworm that is a pest of grasses such fine and tall fescues and all species of bluegrass as well as cereal crops, corn and occasionally fruit tree buds and leaves. The larvae caterpillars start off bright green and gradually become a blackish/brown colour with a bronzy sheen and a lighter coloured underside. Distinctive markings include 3 lighter coloured stripes that run down the length of the caterpillars back. At maturity they measure about 3.5 to 4.5 cm (1 3/8″ to 1 6/8″). The adult moths can range in colour from a light tan to varying shades of reddish/brown, gray/brown, even rosy/brown tones. Their forewings appear to have a series of wavy bands running across the width with a distinctive darker coloured band-like marking running across the middle. They have a wingspan of about 3-4 cm (1 1/8″ to 1 1/2″). The adults lay their eggs in the fall, and they overwinter either as eggs or larvae (that are capable of feeding during the winter if it is mild enough). Photos
• Red-backed Cutworm (Euxoa ochrogaster); caterpillar larvae have 2 broad reddish-brown, translucent stripes that runs down its back. At maturity they measure about 3.5cm. The adult moths have four colour forms.  Photos is primarily a pest of cereals, sugar beet, canola, mustard, and flax in the prairie provinces. It also feeds on most vegetables, sunflower, sweetclover, alsike, alfalfa, various tree seedlings and garden flowers.
• Dark-sided Cutworm (Euxoa messoria) Photos
• White Cutworm (Euxoa scandens)
• Sandhill Cutworm (Euxoa detersa) 
• Army cutworm (Euxoa auxiliaris) Photos

Photo credits: all photos taken by the author.

References:

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