Agronomy Blog

Scouting for Corn Rootworm Larvae

by Steve Crafton | Jun 30, 2017

Rootworm larvae hatch in May and June so the first couple of weeks in July is a good time to dig roots. The following is guidelines to following when digging roots.

  1. You will need a few 5 gallon buckets, tile spade and pressure washer.
  2. Walk 100 feet into plot and select 3 uniform plants evenly spaced plants.
  3. Dig 6-8 inches around circumference of plant and as deep as you can, try to keep the root mass intact.  If evaluating more than 1 hybrid or trait, make sure you label each plant with a water resistant marker.
  4. Soak roots in bucket for 15 minutes.If rootworm pressure is severe you will see them floating in the bucket.
  5. Wash the soil from the roots with a pressure washer. Stand back 3 feet when using pressure washer.We want to remove the soil to evaluate damage from rootworms, not the pressure washer.
  6. Inspect each node of roots accessing damage caused by rootworms.
  7. Use Iowa State Root Rating Scale to rate root damage.
Crafton Root Dig 1Crafton Root Dig 2Crafton Root Dig 3Crafton Root Dig 4
Crafton Root Dig 5Crafton Root Dig 7


Iowa State Node Injury Chart
(Oleson, J.D., Y. Park, T.M. Nowatzki, and J.J. Tollefson. 2005. J. Econ Entomology. 98(1): 1-8)

Crafton Root Dig 6 Chart

Rootworm feeding can cause yield loss with increased lodging, inhibit water and nutrient uptake to the plant, plus provides an entry point for secondary pathogen’s into the plant.  If more than one node is eaten off with each root on the node 1.5 inches or less, best management practices should be implemented the following year:

  • Crop Rotation
  • Genuity® SmartStax® – select a hybrid with a dual mode of action below ground
  • Genuity® VT Double Pro® plus an insecticide

 We have been lucky past few years with frequent timely rains to help roots regenerate if fed on by rootworm larvae. If we experience a dryer than normal year these roots will not have the moisture to regenerate and we will see very high yield losses and stand-ability issues as in years past.  If there is a field that has had issues in the past or multiple years of corn after corn, planting a Genuity® SmartStax® hybrid with 2 modes of action against rootworms in combination with LG Seeds high yielding hybrids will provide optimum protection and yield potential! 

Note: The information in this issue is based upon field observations and third party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions.
Genuity®, SmartStax® and VT Double Pro® are registered trademarks of Monsanto Technology, LLC.
All pictures are courtesy of Steve Crafton, LG Seeds.
LG Seeds and design are trademarks of SCA Limagrain.

Download a copy of this Technical Bulletin: Tech_340 - Scouting for Corn Rootworm Larvae