Watch Fields for Black Cutworm Activity

DECATUR, Ill. (DTN) -- Black cutworm (BCW) moths don't need a Real ID to gain entry to crop fields. They catch a free ride on spring storms coming out of Southern states to arrive in the northerly corn and soybean fields with the purpose of starting a large and very hungry family that dines on young plants.

Illinois Soybean Association Outreach Agronomist Stephanie Porter has been finding significant captures of moths on sticky traps over the past few weeks in central Illinois. "It's a heads up we need to watch fields closely as larvae begin to develop," said Porter.

Most years, early planted crops grow quickly enough to escape black cutworm feeding. However, cool and wet conditions in late April and early May not only kept planters idled in some areas but also slowed the growth of the crop already planted. Add early moth flights, and it sets up a more cautious scouting scenario than normal, Porter said.

The challenge with cutworm is it is a sporadic pest, said Nick Seiter, University of Illinois extension entomologist. "Just because you get significant moth captures does not mean there will be crop injury from larvae. What it does signal is the need to scout and not be complacent," he told DTN.

Seiter won't go so far as to say black cutworms are "smart." He prefers to think of them as crafty or sneaky -- adapting their habits to avoid predators. They also often show up when farmers are busy with other operations, so it's easy to get caught off guard. Here are a few things to know to keep ahead of this pest.

MONITOR PEST REPORTS

Farmers can place sticky traps in fields to monitor activity, but there are other ways to determine if moths are present or if they might threaten, Seiter said. Networks of volunteers tackle the job of reporting moth captures in many states. Check with your specific state pest laboratory or reporting network to get alerts. Here are a few examples:

The IPMPipe website tracks moth flights and projected cutting dates for Iowa, Illinois and Wisconsin: https://corn.ipmpipe.org/….

Iowa: https://crops.extension.iastate.edu/…

Minnesota: https://swroc.cfans.umn.edu/…

Nebraska: https://cropwatch.unl.edu/…

Missouri: https://ipm.missouri.edu/…

Ohio: https://agcrops.osu.edu/…

Wisconsin: https://datcp.wi.gov/…

WATCH MODEL PREDICTIONS

A significant flight of black cutworm is generally defined as the capture of eight or more BCW moths over a two-night period.

Entomologists use historical growing degree day (GDD) data and the occurrence of these significant flights to determine when larvae might start feeding on crops.

For example, the most recent report from the University of Minnesota indicated scouting for leaf feeding from early April flights should begin around May 11 for corn. Larvae from mid-April flights were projected to reach 4th instar and to be large enough to cut small corn the last week of May. Read the most recent report from Minnesota https://swroc.cfans.umn.edu/….

Even if there's a reporting network, not every region has a trap, so it's important to scout ahead of predicted cutting dates, noted a recent Iowa State University release (https://crops.extension.iastate.edu/…).

Corn is most susceptible to black cutworm damage from V1 to V4 (one leaf to four leaf stage). Young larvae, generally less than three-quarter-inch long, will feed on leaf tissue. Older larvae, generally greater than three-quarter-inch long, can cut corn seedlings above or below the soil surface, depending on soil conditions. Cutting rarely occurs once plants reach V5, according to the Iowa release.

Black cutworms can cut soybeans below their growing point, but this is often less of a threat because of the crop's ability to compensate for stand loss. For more information on feeding in soybeans go to: https://extension.umn.edu/…

NOTE SUSCEPTIBLE FIELDS

Black cutworm moths tend to lay eggs in fields that might have had heavy vegetation such as henbit, chickweed and other winter annual weeds or in cover crops prior to planting, noted Seiter. "However, they also seek out grassy areas and waterways for egg laying.

"Fields where you have the potential for large black cutworm larvae to be present when seedling corn or other crops are emerging are likely most vulnerable," he added. Black cutworm infestations can be scattered within a field or found throughout the field.

He recommended scouting in areas where infestations have been found in the past or near these grassy/weedy areas. Low areas within fields are also a good place to focus scouting, he added.

TIME SCOUTING TRIPS

"Black cutworm larvae are nocturnal," Seiter said, observing that this habit is a survival tactic to avoid being consumed by birds.

"If you want to catch them in the act, get out early or when it is cloudy. Otherwise, you might need to do a little digging to find the actual larvae," he added.

If you miss that early or late scouting window, look for wilting, leaf discoloration or missing or cut plants. Black cutworm larvae sometimes drag cut plants under soil clods or into the furrow to continue feeding during the day.

If weeds are being fed upon or disappear without herbicides, it's not just good fortune. Black cutworms may be feeding.

Don't rely on Bt traits to completely protect your corn fields, Seiter added. While some Bt traits supply suppression of these pests, they cannot necessarily withstand a heavy infestation. See more on Bt traits and their target pests here https://www.texasinsects.org/….

Pamela Smith can be reached at pamela.smith@dtn.com

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