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Illinois Pest Survey reports black cutworm cutting dates in five high-risk counties; fields at 1-to-4 leaf stage will be at greatest risk. Take a look at one agronomist's scouting tips.

Jill Loehr, Associate Editor, Prairie Farmer

April 22, 2016

3 Min Read

Early-season pest alerts are spreading as more seed goes in the ground and black cutworm counts are on the rise, says Kelly Estes, agricultural pest survey coordinator.

Estes explained volunteers throughout the state are trapping black cutworm flights. Scouts are looking for 9 or more moths over the course of 2 days.

“That is what we consider a significant flight and we use that to start calculating degree dates from that day forward,” Estes said. “And we know when we hit approximately 300 to 350 growing degree days, there is potential for larvae to be in those areas that are big enough to cut plants.”


That means farmers, especially in the high risk counties like Brown, Christian, McDonough, Piatt and Woodford, should be prepared to scout in early May. Stephanie Porter, Burrus sales agronomist, offers up the following scouting tips:

1. Green means go

Start in ‘green’ areas, where black cutworm will mate and lay eggs, such as weedy areas or fields next to wooded areas. Fields with purple henbit tend to be at higher risk, as well as fields tilled this spring or no-till fields.

2. Check cover crop fields

Porter believes the benefits of cover crops outweigh the negatives, but farmers who plant right into cover crops have a lot of green in fields. “That could be a potential area at risk for pests,” Porter explained. “That’s why researchers recommend killing cover crops 7-10 days prior to planting corn.”

3. Dig and ID


Areas of the field with pin holes in leaves, wilted or cut plants are a big red flag. “The first thing I will do is dig around for the cutworm and 9 times out of 10, in Illinois, it will be a black cutworm,” Porter noted. “Black cutworms cause injury because they cut below the growing point. Some other insects may look like black cutworm, but they don’t cause the same injuries and you may not need to treat.”

4. Verify protection

Fields planted with a Bt hybrid or treated seed may already have protection against black cutworm. “Farmers have already made investments in protection and they may not be aware of it,” Porter said. “So before we start pulling the trigger and spending more money, check and see what’s there.” Porter also noted farmers shouldn’t rely on Bt traits alone. “For Bt to work, cutworms have to eat the plants, so you’ll still get some damage,” Porter said.

5. Check crop stage

Plan to scout from corn emergence to three or four weeks after emergence. Then, factor in the stage of the seedlings. “Once that corn plant gets above 15 inches, we don’t need to worry about it anymore,” Porter said. “That corn plant is too big for the cutworm to cause injury.”

6. Do the math

To calculate a percentage, look at 100 plants per field. Identify 20 different plants in 5 different locations across the field. “With 3% damage, we may pull the trigger on a rescue treatment,” Porter noted.

As the season progresses, there is one more factor to consider. Porter recommended checking the head capsule of black cutworms found during scouting. The bigger the head capsule, the more mature the cutworm and the less feeding will occur.

To stay on top of pest alerts in Illinois, follow Kelly Estes @ILPestSurvey on Twitter. Or, check the IPM Bulletin website.

‘HOT SPOTS’: Estes said black cutworm is a migratory pest that moves north with warm southerly winds. That’s why some counties have ‘hot spots’ with higher counts. “Black cutworms favor areas where they can lay eggs, like fields with winter annual weeds, which seem to be everywhere this year,” Estes said.

About the Author(s)

Jill Loehr

Associate Editor, Prairie Farmer, Loehr

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