Scouting for Corn Rootworm (CRW) Damage


When: During the first two weeks of July, when feeding damage will be most evident.

Bring: Two containers to collect corn roots (pails or feed bags large enough to hold 15 root balls), one clearly labelled “Refuge” and the other “Bt.”

 

Step 1: Dig Up Corn “Root Balls”

a. Collect 15 root balls each from the refuge and Bt areas, beginning with the refuge. Using a shovel, pry the plant out of the ground ensuring not to cut or break off any roots. Cut the stalk of the plant 6 inches above the root ball, shake off the excess dirt, and place the roots in the correct container labeled “Refuge” or “Bt”. Severe feeding by corn rootworm may result in above-ground symptoms such as stunting, wilting, lodging and goose necking. If these symptoms are found in the field, include some of these plants in your sample, or take 15 random plants.

b. Draw a map, GPS the location, or tag plants in these suspect areas for relocation if future sampling is needed

 

Step 2: Wash the Roots

a. Soak the roots in a pail of water for 5-10 minutes to soften the dirt.

b. A garden hose may then be used to remove the soil, with careful attention not to cause further damage to the roots, and being careful not to mix the root balls from the refuge and the Bt corn.

 

Step 3: Rate the Damage

a. Starting with the refuge roots, rate each root ball using the Iowa State Nodal Injury Scale (0.00-3.00) and calculate the average damage from all 15 roots. Repeat this for the Bt corn roots.

b. On a clean root, undamaged tissue will be white to creamy white, damaged tissue is light to dark brown.