Published on Monday, August 19, 2019
Corn rootworm (CRW) is a pest that, if left unmanaged, can cause economic damage in most of the Corn Belt. Damage can result from root-feeding while they are in larval form and from adult beetles clipping silks during pollination.
Root damage due to larval feeding may cause plants to show signs of nutrient or drought stress. In severe cases, the plant will remain short and enter reproductive growth early. Pollen shed and silk elongation take massive amounts of water, and the reproductive efficiency of corn suffers, ultimately reducing yield. After the third instar, the larvae go through pupation, then adult CRW beetles emerge from the soils.
Adults feed on the silks of corn plants and can reduce pollination, resulting in reduced kernel set and lower yield. The corn plant will continue to push silks out until the kernel is pollinated for up to about 10 days. Treatment of adult CRW beetles is usually not an effective method for reducing CRW populations, but severe cases of silk clipping occasionally warrant control. Silks clipped back to ½ in. or less with less than 50% pollination complete is cause for treatment.
Assess Damage: Three Methods
These are three strategies to assess how your rootworm control program is currently working and whether or not to make changes.
Assign a Two-Digit Nodal Root Injury Score
The Traditional Scale (Rating and Damage Description)
Rootworm traits (Bt) in corn make control straightforward. Bt genes produce a protein that is toxic to CRW — the larvae must feed upon the roots to be affected by the protein. In cases of extreme pressure, consider rotating to products with a different protein, or products that express multiple proteins that control CRW.
Control methods beyond Bt traits include soil-applied insecticides and changing crop rotations to include a non-host crop.
Author: Nate Mayer
Categories: Agronomy, Agronomy Talk
Tags: corn, Agronomy, Beck's Agronomy, corn rootworm, corn pests, beetles, corn root damage