How To Read Your Roots for Corn Rootworm Damage

March 31, 2018


There are a lot of risks and pressures when growing corn, but none are more expensive and frustrating than dealing with corn rootworm (CRW) pressure. Scouting is an important part of assessing CRW pressure, but how do you assess the effectiveness of your control tactics? That’s where the root node injury scale comes in.

The root node injury scale ranges from 0.00 (no feeding damage) to 3.00 (three or more nodes have been eaten). Damage to nodes eaten is expressed as the percentage of the node missing (e.g., 1.50 means one full node and 50% of another node pruned within 1.5 inches of crown).

Source: Tinsley, N.A., Estes, R.E. and Gray, M.E. 2012. Validation of a nested error component model to estimate damage caused by corn rootworm larvae. Journal of Applied Entomology. DOI:10.1111/j.1439-0418.2012.01776.x

While there are many ways to scout for CRW, the standard for reviewing the efficacy of corn rootworm control measures is to use the root node injury scale. Root ratings are fairly reliable and efficient indicators of CRW presence and damage. They are able to show a linear relationship between the scale and amount of root injuries, providing greater accuracy while assessing corn root damage.


1. First, you must dig up your corn roots. Roots should be taken from several different locations in your field for a more accurate representation of the entire field.

When CRW larvae feed, they eat away at the roots and leave a brown scarring color. Be sure to dig away from the plant so that you are able to observe that any trimming or pruning of roots you see is from CRW damage and not accidentally from your shovel.

2. Shake off the dirt and clean the roots so you can judge them for an accurate score.

3. Score your roots based on the table above.

Want to see what this looks like in the real world? See examples when you read up on identifying root node injuries.

If you’re finding CRW pressure getting to you, consider investing next season in a corn trait designed to take on the billion-dollar bug: SmartStax® PRO with RNAi Technology. Built on the strong foundation of SmartStax® Technology, SmartStax PRO Technology offers three modes of action for improved corn rootworm control, providing the strongest biotech defense* available today.

ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

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​*69 2021 & 2022 Bayer Trials in the corn belt (KS, CO, NE, IA, IL, ND, SD, OH, MN, & WI) vs SmartStax® RIB Complete® Corn Blend, Agrisure Duracade® E-Z Refuge®, and Qrome® products in the 95-115 RM range with comparable trait packages.