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Cutworms are one of the most damaging pests threatening U.S. corn production. In 2023, Western bean cutworms alone reduced overall corn yield in the U.S. by 87.4 million bushels, a degree of damage second only to that caused by corn rootworm.¹
Different cutworm species pose threats in different geographic locations, but learning how to spot cutworm damage can help you manage this pest and limit its impact on yield.
📸: BASF employee/Featuring an example of a damaged corn crop due to cutworm.
The term “cutworm” is a generic name for multiple species of moths at the larval stage. This pest invades cropland via moth eggs that hatch into ravenous larvae that feed on seedlings. Cutworm damage to young seedlings can be devastating. Adult moths typically do not damage plants, with the exception of Western bean cutworm which feeds on corn ears and causes damage during ear development. Despite the name, this pest has moved further east into the Corn Belt in the past 10-15 years.
Cutworms are active throughout the summer, but aside from Western bean cutworms they are rarely a problem after spring as plants mature. The most severe crop damage due to most species of cutworms occurs early in the season when young plants are small and their tender tissue can easily be cut.
Most cutworm species follow the same general life cycle. However, the timing and length of each lifecycle stage varies from species to species.
For example, black cutworms mate and lay eggs in early spring, whereas dingy cutworms lay their eggs in late summer or fall. The incubation periods of different cutworm species also varies, ranging from two to 14 days depending on species and weather conditions. Furthermore, some species lay a single egg while others lay rows of over 600 eggs.
These factors account for why some cutworms develop rapidly, producing three or four generations per season while others may only produce one generation per season.
Additionally, cutworm populations are affected by weather patterns (especially rain and wind), during migration, resulting in different levels of cutworm damage from year to year. In warmer regions, some cutworm species can overwinter in the soil under crop residue as larvae and pupae, but in colder regions, cutworms migrate north to south each year. These moths rely on the spring southern winds to migrate north. If wind patterns aren't in their favor, or rain events occur during migration, you may see a reduced infestation. Once they make the trip north, most cutworms will go through a few life cycles, but the first generation is the one that will do the most significant damage to corn (the second generation will usually feed on corn that is already too established to damage).²
Tracking migrations with cutworm traps can be a useful tool to gauge the upcoming season's infestation.
📸: ~User3280de91_975, Mediterranean, Vinícius Rodrigues de Souza via Canva and Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org/BASF internal graphic featuring examples of the typical lifecycle for four major cutworm species.
Cutworm larvae emerge and start feeding in early spring. They feed on leaves or small roots until they reach about 0.5" long, then move on to seedling stems, cutting or burrowing into them.
Fields with substantial plant cover or crop residue are an ideal habitat for moths, making no-till fields with winter annual weeds, unsprayed fields or cover crop fields more susceptible to a cutworm infestation.
Cutworms are most prevalent in fields with the following conditions:
Scouting for cutworms every 7-10 days until corn reaches the V5 growth stage is recommended.
Cutworms typically feed in the evening or at night, so you may find evidence of cutworms (damaged or cut plants) without actually seeing the cutworm larvae itself. They tend to hide in plant debris or just under the soil surface during the day.
If you do go scouting for them, look for the following features:
The most significant cutworm species include:
📸:Merle Shepard, Gerald R.Carner, and P.A.C Ooi, Insects and their Natural Enemies Associated with Vegetables and Soybean in Southeast Asia, via Bugwood.org/Image of black cutworm.
📸: James Kalisch, University of Nebraska, Bugwood.org/Featuring an image of a claybacked cutworm
📸: Adam Sisson, Iowa State University, Bugwood.org/Featuring image of a Western bean cutworm
Cutworm damage can easily be confused with damage from other common pest threats to Midwest corn. Know what to look for when identifying which pest you’re up against.
Cutworm larvae begin feeding in spring and continue until early summer, with damage becoming most apparent in June through August. Cutworm larvae begin wreaking havoc on crops by feeding on leaf tissue, resulting in irregular holes in plant tissue. Fourth instar (about half-grown) cutworms can severely injure or cut stalks by feeding at the base.
Different species can cause damage at different parts of the plant:
Corn rootworms are damaging at both the larval and adult stages, with peak damage occurring from mid-June through mid-July. Plants with larval rootworm damage will have root tips that appear brown and are often tunneled into and/or chewed back to the base of the plant. Plants turn yellow and wilt, and if root damage is severe, growing plants can lodge. Around R1, adult beetles start feeding on corn silks. In severe infestations, leaves may be chewed also.
Most damage caused by common stalk borer occurs in June and July. If the stalk borer burrows into the stem of the plant and tunnels upward, damage will appear as wilt and deformities including twisting or stunting. In severe cases, the entire plant may bend over. If the stalk borer enters the leaf whorl, leaves will unfurl with irregular holes where the borer has chewed.
Billbugs feed below the ground or within the crown of the plant. Most damage to corn plants occurs during May. Similar to cutworms, billbugs leave telltale feeding slits on lower stems, creating wilted leaves in the center of the leaf whorl as billbugs clip leaves off from within the stem. Billbugs can cut off leaves and entire seedlings if seedlings are very young. Larger plants may be twisted and as leaf blades unfurl, you will notice a line of holes (often a series of three to four) across the leaf.
Southern corn leaf beetle larvae are typically most damaging to corn from May to July. The larvae may eat into the side of the plant about 1" above the soil surface and the plant may bend over, hindering new leaves from unfurling and growing. Adult beetles feed on the stem and leaves of seedling corn plants. These beetles create distinct notched holes in the leaves as they chew on the edges of leaves and stems.
Wireworm damage is typically exacerbated by cool, wet, early-spring weather. Wireworms feed on seed prior to germination. They destroy seeds by creating holes and tunnels in them. Wireworms also feed on the underground portion of the stem and roots leading to death of seedlings or wilting, poor stand establishment and stunted plant growth. Stunted plants typically are dark or purplish in color.
Partially cut seedlings may recover without major yield consequences, provided they are cut above the growing point. Many times young corn plants are completely cut and will die.
📸:Clemson University - USDA Cooperative Extension Slide Series, via Bugwood.org/Featuring an image of a cutworm at work cutting a seedling.
The chances of a crop recovering from cutworm damage are impacted by:
Going on the defensive is probably the best strategy for managing cutworms. Two defensive strategies to consider are selecting corn seed with Bt traits or using a seed treatment for cutworm.
To manage an existing cutworm infestation, post-emergence rescue insecticide treatments such as Fastac® CS insecticide are also effective if the application can be made quickly while the cutworms are still actively feeding.
Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent, or a professional like your regional BASF representative.
Learn more about how to protect your crop from pests.
Always read and follow label directions. Fastac and Grow Smart are registered trademarks of BASF. Copyright 2024 BASF Corporation. All rights reserved.
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