Agronomy Talk

AGRONOMY TALK: BLACK CUTWORM

Published on Monday, May 11, 2020

Black cutworm (BCW) (Agrotis ipsilon) is an insect pest in many areas of the world. It can cause significant economic damage to corn, soybean, cotton, and other crop species. In the Corn Belt, BCW larvae are primarily known for the damage they cause to newly emerged corn plants. Their feeding can result in cut off seedlings near ground level, thus, the name “cutworm”.

DESCRIPTION AND LIFE CYCLE:

Black cutworm moths have a dark, brownish body with distinctive daggershaped markings on their forewing. Adult moths have a wingspan of approximately 1.5 to 2 in. The moths have a robust body and are strong flyers that can travel long distances. 

The larvae of BCW are light gray to black and their skin has raised bumps with a greasy appearance. When fully grown, BCW larvae are approximately 1.5 to 2 in. long. When disturbed, the larvae will curl into a C-shape. BCW larvae are distinguished from other cutworm species by the arrangement of the tubercles on their back. 

Black cutworm are unable to survive cold temperatures; therefore, it migrates to the Corn Belt from the South each year. The heaviest moth flights typically occur between April and May. After the moths have migrated north, the females lay up to 1,000 eggs starting late March and into April as nighttime temperatures begin to warm. Low-lying areas of fields with dense plant coverage are favored sites for egg-laying. Fields that had high winter annual weed pressure are primary locations to scout for BCW damage during corn emergence. Common winter annuals that are attractive to female moths include chickweed, shepherd’s purse, peppergrass, and yellow rocket. 

It typically takes 35 to 50 days to go from an egg to an adult BCW moth, and multiple generations occur each year. As the season progresses, damage from this pest becomes less important because crop plants become too large for the larvae to cause significant damage.

DAMAGE:

The most significant losses caused by BCW are stand losses early in the season. BCW larvae that are smaller than the fourth instar feed on plants, primarily the leaves; this damage is often called shot-holing. Once the larvae reach fourth instar, they are large enough to begin cutting plants. If soil conditions are wet, the damage may be above ground. If the soil conditions are dry, the larvae tend to stay below the ground and cause damage below the soil surface. Sometimes BCW will cut plants off and pull them into the ground to feed. As the larvae and plants become larger, BCW will sometimes tunnel into the plant and feed on the growing point, resulting in plant death. Most of the damage caused by BCW occurs on plants that are less than 15 in. tall. Larger larvae can cut off multiple plants in one night, so even low larval populations can cause significant reductions to crop stands. 

SCOUTING AND THRESHOLDS:

Scouting for BCW should begin at corn emergence and proceed three to four weeks after emergence or until the stand reaches the V4 or V5 growth stage. Evaluate approximately 25 plants in 10 widely scattered locations for a total of 250 plants. Focus on fi elds that were later-planted and fi elds that had signifi cant winter annual weed pressure near planting. Identify plants with leaf feeding, cutting, wilting, and missing plants. It is benefi cial to gently dig around the base of damaged plants to locate BCW larvae in the soil or under dirt clods. Some researchers recommend a rescue insecticide treatment when 2% to 4% of corn plants are cut below ground or 6% to 8% of corn plants are fed upon or cut above ground.

MANAGEMENT:

Moderate infestations of BCW can be controlled with high-rate insecticide seed treatments like Beck’s Escalate® with Nemasect® seed treatment. When a high-rate insecticide seed treatment is combined with BCW-controlling Bt traits, the level of activity increases signifi cantly. In severe infestation years, using a seed treatment and Bt traits may not provide complete control of BCW. In those rare instances, a rescue treatment with labeled insecticides may be required to protect your corn stands. 

There are a few cultural practices to consider:

  • Scout frequently and apply insecticides if populations exceed thresholds
  • Remove annual winter vegetation a minimum of 14 days before planting
  • Where tillage is feasible, fall or early spring tillage reduces weed cover 

 

Credits:
https://ipm.missouri.edu/pestmonitoring/bcw/identifi cation.cfm
https://www.farmanddairy.com/news/black-cutworms-are-on-their-way/255600.html?icn=top-links https://ipcm.wisc.edu/blog/2016/05/black-cutworms-in-corn/ http://blogs.cornell.edu/ipmwpr/black-cutworm-bcw-agrotis-ipsilon-in-fi eld-corn/ 

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Author: Scott Dickey

Categories: Agronomy, Agronomy Talk

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