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Cutworm

Source:  Cutworms--Entomology Leaflet 69, University of Vermont Extension
by G.R. Nielsen, Former Extension Entomologist, Plant and Soil Science Department

The larvae or caterpillars of some moths are called cutworms* because of the way
they eat, cutting down young plants. The adults are night-flying moths that feed
on nectar, if at all, and do no damage.
Damage: There are a great many species of cutworms. While they all feed on
plants by chewing, they vary as to damage done and host plants preferred.
Generally they destroy more of the plant then they eat. Their numbers vary
greatly from year to year and when numerous may destroy 50 to 75% of a crop.
Cutworms injure plants in four major ways:
Solitary surface cutworms cut off young plants just at, or slightly above or
below the soil line, sometimes dropping the severed plants into their burrows.
Because most of the plant is not eaten, these cutworms do great damage
attacking and felling new plants nightly. The black, bronzed, clay-backed,
dingy cutworms are in this group.
Climbing cutworms--usually the variegated and spotted ones--climb the stem of
trees, shrubs, vines, and crops and eat the leaves, buds, and fruit.
Subterranean cutworms--such as the pale western and glassy--remain in the soil
and feed upon roots and underground parts.
Army cutworms occur in great numbers, consuming the tops of plants and then
marching on to other fields (see EL #56).

Description and Life History: There are many species of cutworms. Many are
stout, smooth, soft-bodied, plump caterpillars. These vary from brown or tan to
pink, green, or gray and black. Some are all one color, others spotted or
striped. Some larvae are dull, others appear glassy. The adults are generally
very robust brown or black moths showing various splotches, blotches, or stripes
in shades of gray, brown, black, or white.

Most cutworms pass the winter as partially grown larvae. Thus they already are
large voracious feeders at the time transplants and seedlings are set out in the
fields. A few species pass the winter as pupae or hibernating moths.
Overwintering cutworms may live under trash or bark, in clumps of grass, or in
earthen cells in the soil. These cutworms become active and begin feeding as the
weather warms in spring, remaining hidden under debris or in the soil and
feeding at night. Many species continue to feed well through June, then pupate
in the soil and later emerge as the moths. Normally there is only one generation
per year. The moths crawl from their brown pupal case in the soil and climb up
through the soil, following the tunnel made by the earlier descending larva.
If this tunnel is blocked, the fragile moth cannot escape the soil. Cutworm
abundance and development is greatly affected by weather, especially rainfall.

The moths mate and lay eggs in late summer, beginning the next generation. The
moths often seek out grassy or weedy areas to lay their eggs, which are usually
deposited on plant stems or in the soil. One female may lay hundreds of eggs.
The hatching larvae feed until cold weather and then hide for the winter in a
sheltered, dry place.

Control: Several cultural practices may offer some degree of control.
Mid- to late summer plowing and fallowing of fields often results in no eggs
being laid in these fields.
Fall plowing exposes larvae or deeply buries the pupae.
Cultivating fields in spring after vegetation has appeared and grown a few
inches, followed by delayed seeding, often starves cutworms.
Planning rotations to avoid row or hill crops following a grassy sod may help.
Plow sod fields in late summer or early fall the year before planting.
Cultivating frequently injures and exposes hiding cutworms to predators.
Constructing ditches and dusty furrows may interrupt armyworms.

In addition gardeners may try the following:
Place foil or paper wraps or cardboard collars around transplants; extend a
few inches into the soil and several inches up the stem.
Dig in the soil around damaged or adjacent plants in the row; find and destroy
the cutworm.
Plant a thick "trap crop" of sunflower, a favored host, around the perimeter
of the garden; find and destroy attacking cutworms daily.
Use tanglefoot on trees being attacked by climbing cutworms.
Other suggested home remedies include the following:
Catching and placing toads in the garden.
Wrapping onion stems around the stems of transplants.
Placing a ring of moist wood ashes around the plants.
Placing a toothpick or 16d nail alongside each transplant stem.
Chemical treatments are available as either homemade or commercial poison baits
or as insecticide treatments directed to the soil surface or on and around the
plants. Granular insecticide treatments applied to protect the seed and
developing seedlings from soil insects are of little, if any, value in
controlling cutworms.
For currently recommended insecticide controls, refer to a current issue of BR
1158, "Insect and Disease Control in the Home Vegetable Garden."

*Cutworms, (Agrotis, Amathes, Peridroma, Prodenia spp. and others, Lepidoptera,
Noctuidae).

Before using any pesticide, read the label and follow all precautions!
Edited in June 1997, based on material developed in 1985.
Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30,
1914, in cooperation with the United States Department of Agriculture. Lawrence
K. Forcier, Director, University of Vermont Extension, Burlington, Vermont.
University of Vermont Extension and U.S. Department of Agriculture, cooperating,
offer education and employment to everyone without regard to race, color,
national origin, sex, religion, age, disability, political beliefs, and marital
or familial status.
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Last reviewed April 10, 1998.