Find out if you need to scout corn for Western Bean Cutworm

Category: Grow Grain

Western Bean Cutworm moths are flying. If your field matches these conditions, you could be at risk. Here’s what to watch for.

As part of our Growing Series 2016-17 season, we’re bringing you timely agronomic advice to help you achieve your yield goals. More and more corn growers in Ontario are facing the threat of Western Bean Cutworm (WBC) in their crops. Peak moth flight is approaching fast. If you’re in a hotspot, it’s time to plan your control strategy.

Photo showing a cluster of white Western Bean Cutworm eggs on a corn leaf.

When to scout for Western Bean Cutworm

Adult WBC moths lay their eggs on the crop during the last half of July. Typically, this is when corn comes into tassel. Within a week, the egg masses turn from white to purple and then hatch. New worms feed their way into the cob through the side or the silks. The best time to control Western Bean Cutworm is once eggs have hatched and worms have started travelling down towards the cob. 

Scout for egg masses on upper leaves if you have these field conditions:

You’ve had Western Bean Cutworm in that field in the past.

WBC can overwinter as larvae in soil chambers and put pressure on your crop year after year.

You’re farming in one of the WBC hotspots in Ontario.

Moths can fly into new fields, so hotspots are spreading. Even if you haven’t had Western Bean Cutworm in the past, scout fields this year if you’re near a hotspot. Check out the Canadian Corn Pest Coalition’s website to view an interactive map of WBC moth trap counts in Ontario.

Your crop’s tassels emerge after or during peak moth flight.

Moths prefer to lay their eggs on corn before the tassels are out. In late-planting years like 2011 and 2014, tassels emerged near August long weekend, which was later than peak moth flight. Moths laid a lot of eggs and we saw high damage from WBC. 

If tassels have not emerged by mid-July this year, scout fields.

You crop’s tassels emerge later than neighbour’s field.

If neighbouring corn fields are maturing ahead of yours, scout for eggs. Moths will be attracted to your field if it’s one of the few still at the pre-tassel stage when they start laying their eggs.

You’re growing corn on sandy soil types.

WBC larvae can overwinter in a field, and entomologists have found that they prefer sandy soils.

You have a corn on corn rotation.

You may already have WBC pressure in your field from last season, and since the pests can overwinter, you can expect to see them again this season.

Tips to control Western Bean Cutworm in corn

You can spray insecticide from the pre-tassel through to the full tassel stage. Scout affected fields and watch for WBC eggs to turn purple – a sign that they are about to hatch. Aim to control the worms in the 5-7 day window where they travel from the top leaf down to the tassel. That window can be tricky to obtain due to crop height. Unless you can secure an aerial applicator at a guaranteed time, I encourage you to consider a product with residual activity and ground application.

Matador® offers good knockdown of young WBC larvae. Coragen® has good residual activity, will control the larvae still in the egg masses, and is relatively safe. There’s a good product called Voliam Xpress® that is a combination of the actives in Matador and Coragen, giving you both good knockdown and good control.

If you can’t spray every acre, focus on areas of the field that are slightly behind in tassel emergence and on sandy areas.

Conveniently, WBC control timing lines up with corn fungicide timing. Most disease-control products can be tank mixed with your insecticide. Check out our blog post on corn fungicides for disease management tips.

The economic threshold of WBC: 5% of plants have egg masses on upper leaves

Some corn hybrids offer suppression of Western Bean Cutworm feeding and will protect you from yield losses. However, you may still run into quality issues if there are open cobs at harvest along with rain or delayed combining. If 5% of plants in the field have egg masses (one in 20 plants), spray an insecticide.

I encourage you to reach out to me or your local Cargill agronomist if your field meets any of the conditions I mentioned above. We want to help you protect your corn yield and quality, so let’s talk about a Western Bean Cutworm control strategy for your farm.


Coragen® is a registered trademark of E. I. du Pont de Nemours and Company or its affiliates. Matador® and Voliam Xpress® are registered trademarks of a Syngenta group company.

Tags: Ontario, crop protection, corn, insecticide

1 Comment

  • Eric Richter said Reply

    You forgot to mention if the grower planted Viptera traited corn hybrid, the grower is completely protected. This is the best solution for your growers to control this pest with least environmental impact. Growers also have full grain marketing options. ER

Add a Comment