How To Manage Corn Rootworm: The Billion-Dollar Bug

July 15, 2020

Corn rootworm (CRW) is a serious pest that can cost U.S. farmers around $1 billion every season due to their feeding, which leads to costly root damage and stalk lodging. In this article, we asked Channel Seedsmen to provide real advice from the field to help you learn the when, how and what behind these bugs:

When to expect CRW emergence

How to scout in your field and what to look for

What you can do to prevent an infestation

When to Expect Corn Rootworm Emergence

You may have heard that CRW eggs start hatching around the same time that fireflies start to come out. But a more accurate way of estimating is to look at the accumulation of growing degree units (GDUs). Research has shown that about 50% of CRW eggs may hatch from 684 to 767 accumulated GDUs.

“We’re starting to see CRW earlier than usual this year because we had an early planting season and our growing degree units are ahead of schedule. So timing-wise, we’re seeing more damage than usual — plus we’re pretty dry over here, so that compounds the issue.”
-Brandon Moe, Channel Seedsman, Iowa

These are the three developmental stages that CRW go through:

  • Larval: Slender and cream-colored with brown heads and a dark plate on the top side of the tail. Depending on the maturity, larvae can be between 1/8 inch and 1/2 inch long. The larval stage has three developmental phases that last between seven and 10 days before pupation.

  • Pupal: White, somewhat translucent and is sessile and dormant.

  • Adult: Also known as CRW beetles. Yellow or green with a black stripe along the sides of the wing covers. Adults will be about 5/16 inch long.

If you can catch CRW larvae before your plants are too large to cultivate, you can try to maintain control by applying an insecticide ahead of cultivator shovels during a layby cultivation. But if you wait until midseason (June-July), it’s almost always too late to do anything about root damage.

How To Scout and What to Look For

Suppressing adult CRW beetles with insecticide applications can help reduce the overall larval population the following year. However, adult control methods should only be viewed as one piece of your overall management strategy. Sticky traps are a good way to scout for adult CRW beetles and estimate future populations in your fields.

Be sure to also evaluate your plants for silk clipping. Although there are no thresholds in place for silk clipping damage based on beetle numbers, an average of at least 10 beetles per ear can usually affect pollination. Severe silk feeding (silks clipped within 1/2 an inch of the ear) at 25%-50% pollen shed may indicate a need to apply an insecticide, especially in seed production fields.

“If you start seeing four or more larvae per root, there’s a higher likelihood of root damage for that plant.”
-Brandon Moe, Channel Seedsman, Iowa

Digging roots too early can underestimate the amount of root injury, but roots dug too late can be more difficult to wash and rate due to root regrowth. There’s usually an ideal two-to-three-week window for conducting root digs, which depends on region, planting date and crop stage.

This type of scouting for CRW is just one example of how Channel Seedsmen deliver value during their Field Check Up Series visits. Ask your Seedsman for more information about how they can bring their expertise to your farm.

What You Can Do to Prevent an Infestation

The best way to fight CRW is to be proactive and know their life cycle. Adult beetles lay eggs in the soil at the base of the corn plants, and their newly hatched larvae feed on corn roots at the beginning of next season. So changing your crop to soybeans the next season is one way to reduce the likelihood of CRW issues.

“A lot of our Field Check Up Series visits start as a way to get ahead of any potential issues and find out what’s going on underground with the roots — especially for our continuous corn growers.”
-Dan Kallem, Channel Seedsman, Iowa

In addition to crop rotation, choosing the right products can dramatically reduce the risk of damage caused by CRW. Consider preventing damage to roots all season by planting products with SmartStax® technology to help maintain maximum control over above- and below-ground pests.

“SmartStax® technology is still by far the best choice out there for corn rootworm control.”
-Brandon Moe, Channel Seedsman, Iowa

There’s no denying that corn rootworms are a devastating pest. But with the right planning and tools, you can cut down their potential damage significantly. For the best way to fight CRW in your fields, consult your local Seedsman.