In many crop fields across the United States, one notorious pest poses a significant economic threat to corn: the black cutworm (Agrotis ipsilon).This insect wreaks havoc on corn crops, causing substantial yield (and financial) losses for farmers. 

Recognizing the black cutworm’s distinct characteristics and behaviors is paramount to combat its detrimental impact. With the right knowledge, farmers can implement targeted management practices — and protect corn crops from the destructive forces of black cutworms.

Black cutworm life cycle

Because of black cutworms’ relatively short life cycle, one year could see three generations of the pest. That life cycle spans two to three months (depending on temperatures and the availability of host plants), and includes four stages:

Egg Stage: In the fall, black cutworm moths deposit their eggs on vegetation or crop debris in Midwestern fields before migrating to the southern U.S. Throughout the winter, these eggs patiently wait for spring, then hatch when soil temperatures reach around 50ºF.

Larval Stage: As the soil warms up, the tiny larvae emerge from their eggs and begin feeding. Initially, they sustain themselves on weeds or cover crops until their preferred host plants, such as corn and soybeans, become available. Recognizable by their black to gray bodies, these larvae can grow to 2 inches (50 mm) long. They often feed on plant stems at or just below the soil surface, which causes plants to wilt and perish.

Pupal Stage: After completing their voracious larval phase, the cutworms retreat into the depths of the soil, where they form pupae. This pupal stage lasts approximately two weeks, during which significant transformations occur within the soil. During this time, black cutworm worm-like larvae will turn into winged moth-like adults that are dark gray, black, or brown color with black circular markings on the outer edge of their forewings.

Adult Stage: Finally, the adult black cutworm moths emerge from their pupal cases, ready to take flight. Equipped with robust wings, these moths can traverse long distances. However, they can’t withstand harsh winter conditions, and eventually migrate back to southern climates. In spring, they return to the northern regions, where they seek suitable locations to lay their eggs and repeat the cycle.

In-field damage

To identify black cutworm infestation, check emerging corn or weeds for leaf damage. In certain scenarios, the larvae first feast on and sever weeds before progressing to corn. Larvae pose a significant threat to corn crops, particularly during early growth stages. The damage’s extent depends on several factors, including the larval population, the plants’ growth stage, and the duration of feeding. 

Cutting typically begins around the fourth instar, as the larvae mature. At this stage, the cutworms can clip the plant at or below the soil surface, leading to stunted growth and wilting. A single cutworm can decimate three to four plants. 

For plants that have been severed by black cutworms, assess potential recovery during the V6 stage, where the growing point emerges above the ground. In most cases, if the corn plant has been cut off after this stage, it will not survive. This can reduce stands and yield potential in the field. 

Scout early. Scout often.

Maintain a vigilant watch over fields, particularly during a corn crop’s initial growth stages, where black cutworms do the most damage. Telltale signs of cutworm damage can include wilting plants, cut stems, and distinctive feeding holes in the leaves.

Cutworms seek protection beneath the soil surface during the day and emerge to feed on plants at night. So don’t be surprised to come across the culprits themselves when inspecting soil during daylight hours.

Conduct weekly scouting for three to four weeks following full corn emergence (VE). On extensive acreage, prioritize highly susceptible areas, such as weedy or residue-rich fields. Sampling multiple locations will provide a comprehensive assessment of cutworm activity. Keep records of field observations, noting the number of cutworms and the extent of damage in each area of the field(s). 

Should leaf feeding damage reach 3-5% of total leaf surface area, or the count of cutworms exceeds two per 100 plants, a targeted insecticide application may be warranted.

Remember, early detection is key to mitigate severe black cutworm damage. Maintain regular field monitoring and implement necessary measures to minimize these pests’ impact.

Control methods:

One rescue strategy for fields with black cutworm history could be intensified tillage practices. This can minimize weed presence, which can contribute to an elevated black cutworm risk. (Those weeds provide a readily available food source for the pests.) Defense against the pest can also be bolstered by an insecticide or seed treatment during planting, such as PONCHO® VOTIVO® and PONCHO® 1250 VOTIVO®, or AgriShield® MAX.

While these measures can help reduce insect pressure and feeding, they do not guarantee complete control over the pest. During the growing season, implement pheromone trapping to gain insights on black cutworms’ presence. Comprehensive scouting also remains highly recommended. 

Combining two or more of these management strategies is best, as you can fortify your defenses and make informed decisions to protect yields.

The bottom line

• Black cutworm poses a significant threat to corn crops across most parts of the United States. These pests can be identified by their dark gray to black larvae, grainy skin, and a dark brown head.
• The life cycle of black cutworms spans approximately 2-3 months and progresses through 4-6 instars. They begin causing damage at emergence (VE) and continue until the approximately eighth leaf collar stage (V8).
• To mitigate black cutworms’ impact, scout early and frequently. Focus on highly susceptible areas and diligently record your observations. These efforts will help determine the need for a rescue insecticide application.

If you suspect black cutworm feeding or detect their presence in your fields, don’t hesitate to seek assistance from an AgriGold agronomist. They can help identify the issue and provide guidance on whether an insecticide treatment is necessary. 

With vigilance and expert advice, you can effectively manage black cutworm infestations — and protect your corn crop.