Black Cutworm Fact Sheet - Penn State Entomology Department Fact Sheet

BLACK CUTWORM
Agrotis ipsilon (Hufnagel)

The black cutworm occurs throughout much of the United States. Although it has been present in Pennsylvania for many years, it had not caused extensive crop damage until 1980. The black cutworm, then, is not a new pest, but rather an old one that raised havoc in a new area.

During June 1980 damage was abrupt and severe. Cutworms caused serious plant damage in many localized areas. No region of the state completely escaped its damage; however, losses were highest in the south-western quadrant.


Black Cutworm Larva © Marlin Rice Iowa State University		Black Cutworm Damage Dennis Calvin Collection Penn State University

We could not establish any characteristic pattern that related to the infested fields. Neither the type of ground cover nor the lay of land seemed to have any influence on the targeted fields. We do not know if the 1980 outbreak was a transient problem or if the black cutworm will continue its devastation in Pennsylvania in future years.

The surprise invasion of the black cutworm in 1980 left 50 to 80 percent of the plants wiped out in at least 5,000 acres of corn. Losses to other crops were minimal compared to corn.

Description

Newly hatched larvae are about 1/4 inch in length and when fully grown are nearly 2 inches long. Their color ranges from gray to nearly black. There is a pale rather indistinct narrow stripe along the center of the back. The texture of the skin is characteristic and distinguishes them from all other cutworms. The skin texture consists of convex, rounded, coarse granules with smaller granules interspaced between. Magnification to five times or more is needed for this characteristic to be readily seen.

The moths are similar in size and shape to other species of the cutworm family. There are no distinguishable markings that easily separate black cutworm moths from other cutworms. They are brownish in color with black slashes near the outer edges of the front wings.

Eggs are laid in clusters of 10 to 20. They are white, globular, and sculptured with numerous vertical ridges.

Black cutworm adult moths
expanded and folded.

Dennis Calvin Collection
Penn State University

Life History

There are three generations per year. The insect overwinters as pupae in the soil and also as adult moths. Eggs are deposited in April and May for the first generation. Development from egg to adult requires approximately two months, of which one month or more is in the larval stage.

The number of black cutworms that overwinter in the state is relatively small and does not seem sufficient to trigger outbreaks of infestation. Rather, outbreaks of black cutworm appear to originate from moths that migrate into the area on storm fronts during April and May. As the moths drop out of the storm systems, they deposit their eggs in the area where they alight. The majority of eggs are believed to have been laid before the crop is planted.

Damage

Black cutworms exhibit two types of feeding patterns depending upon the amount of moisture in the soil and size of plants. Where soil moisture is adequate and plants are small, the larvae hide in the soil during the day and move to the soil surface at night where they cut off plants just above the soil surface. This is typical of most species of cutworm damage. One larvae will cut off an average of five corn plants during its development. In situations of dry soil conditions, the larvae do not move to the surface to feed, but instead, they chew into the plant just below the soil surface. This causes the corn plants to wilt and usually die.

Loss of plants in infested fields will vary from 10 to 80 percent. Seldom is a field completely destroyed, but rather, severe damage is usually confined to portions of the field.

Black cutworm damage to corn from early feeding on leaf.

Black cutworm damage to corn
from early feeding on leaf.
© Ed Rajotte
Penn State University

Control

Methods used to prevent infestations can not be relied upon to prevent damage. "Rescue treatments" with an insecticide or poisoned bait application appears to be the most reliable alternative. This treatment should be implemented as soon as cutworm activity is noticed and before substantial losses occur. Insecticide treatments applied to dry soil can not be expected to provide effective control because of the subterranean habits of the larvae under dry conditions. Rescue treatments for black cutworms on vegetable crops are limited.

Check the Agronomy Guide or consult with your pesticide supplier or county agent for details of pesticide use.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

*** Disclaimer ***

Authored by: Stanley Gesell, Extension Entomologist, 1980

Dennis Calvin, Professor of Entomology

Placed on web April 19, 2000

© The Pennsylvania State University 2002
This publication is available in alternative media on request.
Penn State is committed to affirmative action, equal opportunity, and the diversity of its workforce.

Return to Entomological Notes Listing