Feb 21, 2017, 9:00 AM
Every year, we see corn root worm issues moving further and further north. Some farmers have been dealing with this for years, while others are just experiencing it for the first time. I don’t see any region as “off limits” to this yield robbing monster. Corn root worm is considered to be the most damaging of all corn pests, causing more than $1 billion in annual lost revenue in North America.
Option 1: Washing the Roots and Flotation
Option 2: Hand-Sorting of Soil
Two randomly selected plants in each of at least 20 areas of the field should be checked. As you carefully approach each plant, watch for and record any rootworm beetles that drop from the plant or fly away. Grasp the silks in one hand to keep any beetles from leaving them while you inspect the remainder of the plant. After sampling the whole plant, slowly open your hand and count the number of beetles on or within the silks. Examine the silks thoroughly since beetles may be deep in the ear tip area. If there is a second ear on the plant, look through it’s silk as well. Repeat the procedure for the second plant that is within 10 feet of the first plant. After sampling all plants, determine the average number of beetles per plant.
Conduct beetle counts in fields planted to corn consecutively for two or more years. Next season, rotate to another crop or treat for rootworm larvae at cultivation or planting, if the average beetle count per plant equals or exceeds the number listed below for your average number of plants per acre.
Chart 1: Treatment Threshold Chart for In-Season Beetle Counts
Information and chart source: https://extension.entm.purdue.edu/fieldcropsipm/insects/corn-rootworms.php
Example of larvae.
Example of infected ear of corn with corn root worm beetles.
Right plant shows healthy root system. Left plant shows weak, small root system of a corn root worm infected plant.
Example of “goosenecked corn” that’s blown over and then begun to try and regrow upright.