How to Protect Your Conventional Corn from Rootworms

LeRoy Toohey

Sep. 24, 2019

Three species of corn rootworm—the western corn rootworm (WCRW) and northern corn rootworm (NCRW), which share a similar life cycle, and the southern corn rootworm (SCRW), also known as the Spotted Cucumber beetle—cost U.S. farmers around $1 billion every year when factoring in yield losses and input expenses.1

Corn rootworms can be found throughout much of the corn belt, and there is significant variability in rootworm feeding within individual regions. 

An individual corn rootworm can lay anywhere from 500-1,800 eggs, depending on the species. Fortunately, many eggs fail to hatch due to the presence of predators, soil factors, extreme temperatures and excessive rainfall. 

But the corn rootworms that do hatch can pose a significant threat to the health of your crop. All corn rootworm larvae prefer to feed on corn roots, causing the most damage and yield loss, and mature larvae inflict further injury by feeding on lateral roots and burrowing into roots.

Given the potential impact posed by corn rootworms, let’s discuss some options as you get ready for the next planting season so you can protect your crop and increase profit potential for your farm operation.

Is traited corn worth the investment?

One way to limit the effects of corn rootworms is to plant rootworm traited seed, but this can be a costly option. Is traited corn worth the investment? In many cases, the answer might be no. 

Rootworm traits won’t protect your corn from all soil pests. There are no known transgenic traits that control wireworm, white grubs or seed corn maggot--just to name a few. In response to this, some farmers use both rootworm traited seed and a soil-applied insecticide. 

But if traited seed is outside of your budget and cannot give you the control you desire, you may want to consider planting conventional corn instead.

Seed treatments and soil-applied insecticides

With conventional corn, you can manage corn rootworms and other below-ground pests using seed treatments and soil-applied insecticides without spending excessive amounts on traited seed. 

Insecticides are broad-spectrum and placed where they are needed in order to be effective. Soil-applied placement protects roots, and timely foliar applications can preserve above-ground tissue. Unlike traited corn, plant feeding doesn’t have to occur to kill the insect. 

To control or suppress corn rootworms and most below-ground pests, consider trying soil-applied granular products such as Aztec® 2.1G, Counter® 15G, Force® 3G, Fortress® 5G, Lorsban® 15G and generic equivalents.

If you are using starter fertilizer, in-furrow products like Annex® LFR, Capture® LFR or other Bifenthrin brands with either LFR or LFC formulation are a valid choice. Other liquid delivered products that work well for soil applications include Willowood Lambda-Cy 1EC and generic equivalents. 

When using any insecticide, always remember to read and follow label instructions. Also, be sure to do your homework through scouting and sampling to determine the right treatment strategy for your fields. 

Considerations for crop rotation

Crop rotation breaks up the life cycle of corn rootworms, and it is still considered one of the best cultural practices to limit the impact of the rootworm species. 

Keep in mind if you have heavy foxtail and/or volunteer corn in this season’s soybean crop, you may need to use a soil-applied insecticide before planting corn in that field next season. 

Certain NCRWs have developed a type of resistance to crop rotation known as extended diapause, meaning NCRW eggs may wait two or three years before the larvae hatch. In this scenario, if high populations of NCRW are noted in your soybeans, treat your corn with soil-applied insecticide when you plant corn-on-beans. 

Some WCRW rootworm variants also lay eggs outside of cornfields, particularly in soybean fields, making crop rotation less effective. Here again, use soil-applied insecticides to control larvae. 

Choose the best strategy to control corn rootworms on your operation 

Rootworm traited hybrids have their place, but their benefits come with a price. Keep in mind that not all corn rootworm pressure is the same from field to field, and you know your fields and crop rotations better than anyone. 

If you believe rootworm pressure is low to moderate or you plant in a soybean/corn rotation, consider planting conventional corn with a broad-spectrum insect management strategy to maximize your ROI next season.

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LeRoy Toohey

Sep. 24, 2019