Insects and Mites

Black Cutworm

Scientific name: Agrotis ipsilon
Order: Lepidoptera
Family: Noctuidae

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Info

Biological Description
  • Moths: Brown forewings with dark brown to black leading edge. Forewings also have a dagger mark two-thirds of the way towards the outer edge, and a white band across the width near outer wing edge. Hind wing is white with dark veins.
  • Larvae: Black to pale gray and look greasy. Larvae curl up into a tight c-shape when disturbed. Mature larvae are 1½ inches long and have a grainy or pebbly texture.
  • Pupae: Dark brown and ¾ - 1 inch long and ¼ inch wide.
  • Eggs: Laid singly or in groups up to 30.
  • Larvae confused with: other cutworms
Economic Importance
  • Damage is not common in field corn but heavy infestation can occur.
  • Primarily an early season pest.
  • Outbreaks:
    • During an outbreak, late-planted corn is more susceptible to damage.
    • Economic damage is more common when weeds are destroyed at or immediately before planting.
    • There is an increased risk of infestation if there is heavy spring weed growth, newly broken sod, and previous crop and plant debris
  • Susceptible crops:
    • Corn
    • Vegetables, cotton, tobacco, turf grasses
    • Some weeds
Life Cycle
  • A small population of black cutworms overwinters in Wisconsin, however damaging populations come from moths that migrate to Wisconsin in May.
  • Females lay eggs either singly or in clusters.
    • Preferred hosts: Low-growing vegetation such as chickweed, curly dock, mustards, or plant residue from the previous year's crop. Corn planted after soybeans is often a preferred oviposition site.
    • Generally adults will not lay eggs in fields that have already been planted
  • Larvae pupate in soil ¾ - 4 inches deep. Pupation time varies depending on the temperature. At 60°F pupation takes 34 days, while at 74°F only 12 days are required.
  • Generations:
    • There are three generations per season.
    • The first larval generation, active during May and June, is the one that causes the most damage.
    • Peak adult flights are in June/July, July/August, and September/October.
Damage/Symptoms
  • Cutworms are most problematic in low, wet, grassy areas.
  • Damage is a result of larval feeding.
  • Young larvae feed on leaves and cause a "window pane" appearance on the leaves because they cannot chew entirely through the leaf surface.
  • As larvae mature, signs of feeding are pinholes in the leaves and often complete defoliation.
  • When larvae are at the "cutting" stage they are ½ inch long and cut the stem at, or just below the soil surface. This type of injury is common during extended periods of dry weather.
  • When corn is in V3-V4 stages, larvae may not be able to cut plants, and instead burrow into the plant from below ground level. The resulting symptom is wilting of newly emerged leaves referred to as "wilted whorl" or "dead heart."
Scouting Procedure and Economic Threshold
  • Timely detection is critical in order for post-emergence insecticide treatment to be effective.
  • Corn is most susceptible during the first ten to fourteen days after corn emergence.
  • Scout as soon as corn emerges from soil. Examine 50 plants in each of 5 locations (250 plants total) in a field.
  • Threshold 1:
    • When damaged plants are found, dig around the base of the plant for live cutworms.
    • Collect at least 10 larvae and determine their age by the size of their head capsule.
    • Consider treating when approximately 5% of the plants show damage AND cutworm larvae are sixth instar or smaller.
  • Threshold 2:
    • Consider treatment when 6-8% of seedlings are fed upon or cut above ground, or when 2-4% are cut below ground. If plant population is low, use the lower percentage; if plant population is high, use the higher percentage.
  • Pheromone traps are useful for monitoring moth activity, but do not correlate well with whether damage will occur.
  • Degree days can be used to determine when larval feeding will occur if a population is present. The start date for accumulating degree days (or "biofix") is determined by the number of moths caught in a pheromone trap. Start accumulating degree days when eight male moths are caught in a two night period. Plant cutting begins when the cutworms are in their fourth instar, which occurs at 300 Farenheit degree days (FDD) (167 Celsius degree days (CDD)) after the biofix, and continues through pupation, which occurs at 641 FDD (356 CDD). For more information on calculating degree days click here.
Integrated Control
  • Natural control: Heavy rainfall may disrupt egg-laying. Flooding may force larvae to soil surface during the day where they are attacked by parasites or predators.
  • Cultural control: Keeping weeds controlled will lessen the possibility of problems, since adults prefer to lay their eggs in weedy locations. Removing winter and early spring vegetation at least 1-2 weeks before planting can help reduce problems by causing larvae to starve before planted corn becomes available. Avoid planting susceptible crops in low wet areas or in rotations following sod. Any practice that encourages rapid seedling growth would also help reduce damage because larvae only cause damage to seedlings smaller than the 6-leaf stage. When possible, avoid planting into corn with a history of cutworm problems, or after fields have been in pasture, meadows, alfalfa, or red clover for multiple years.
  • Biological Control: A number of braconid parasites wand predaceous ground beetles help keep cutworm numbers down. Birds also feed on cutworms. Some Bt corn hybrids offer partial control of black cutworms.
  • Chemical Control: For current Wisconsin recommendations, consult University of Wisconsin-Extension Bulletin #A3646, Pest Management in Wisconsin Field Crops.

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