Corn rootworm (CRW) larvae and adults cause economic loss every year. The impact of CRW larvae on yield varies greatly depending on:
Plants with damaged root systems are more susceptible to drought stress and lodging. Adult CRW feeding on corn silks during pollination can cause poor seed set and subsequent yield loss.
This pest’s ability to evolve has made crop rotation ineffective in many areas. The soybean variant western corn rootworm has evolved to lay eggs in non-corn fields. The northern corn rootworm has shown extended diapause, in which eggs remain viable in the soil for several years before hatching. Additionally, resistant populations have now been documented for all four commercially-available Bt proteins for CRW control.
Figure 1. Corn rootworm larvae.
Figure 2. Severe corn rootworm feeding damage.
Figure 3. Northern (left) and western (right) corn rootworm beetles.
Figure 4. Left: Gravid female western corn rootworm beetle. Right: Western corn rootworm eggs squeezed from the abdomen of a female beetle.
A yearly scouting program is the first step to effective management, because corn rootworms can rebuild their populations rapidly. Monitor larvae and adult beetle numbers to predict potential egg laying and future problems. The level of rootworm feeding and beetle activity will determine the best management options. Incorporate several of these options to effectively control CRW with an integrated approach.
"Consider an insecticide treatment if the number of beetles averages 0.75 or more per plant and 10% of females are gravid with eggs."
Be sure to alternate modes of action when using insecticides. When using corn hybrids that contain Bt traits for corn rootworm control, it is essential that refuge acre requirements are followed. Failure to comply with refuge requirements and lack of control of adult beetles within the refuge acres will only accelerate the pest’s ability to develop resistance.
Areas with high numbers of adult corn rootworms should consider incorporating a beetle suppression program that utilizes foliar-applied insecticides. This should help reduce the amount of egg laying and potential problems in the future.
Table 1. Insecticide treatments for adult corn rootworms. Always read and follow product label directions.
IRAC Mode of Action Classification:
Group 1 = Acetylcholine esterase inhibitors: 1A = Carbamates, 1B = Organophosphates
Group 3 = Sodium channel modulators: 3A = Pyrethroids, Pyrethrins
Group 4 = Nicotinic acetylcholine receptor (nAChR) competitive modulators: 4A = Neonicotinoids
Group 22 = Voltage-dependent sodium channel blockers: 22A = Oxadiazines
R = Restricted-use product
* Resistance to the pyrethroid insecticide bifenthrin has been documented in corn rootworm in southwest Nebraska.
1Data based on average yield advantage in efficacy trials 2019-2020 with moderate to high corn rootworm pressure. Four hybrid backgrounds per treatment per location.
Qrome® products are approved for cultivation in the U.S. and Canada. They have also received approval in a number of importing countries, most recently China. For additional information about the status of regulatory authorizations, visit http://www.biotradestatus.com/. Agrisure® is a registered trademark of, and used under license from, a Syngenta Group Company. Agrisure® technology incorporated into these seeds is commercialized under a license from Syngenta Crop Protection AG. YieldGard®, the YieldGard Corn Borer design and Roundup Ready® are registered trademarks used under license from Monsanto Company. Liberty®, LibertyLink® and the Water Droplet Design are trademarks of BASF. Herculex® insect protection technology by Dow AgroSciences and Pioneer Hi-Bred. Poncho® and VOTiVO® are registered trademarks of BASF.
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