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FMC Upside Hatchtrak
Insecticides & Miticides

The Effect of Cold Weather on Corn Rootworms

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our technical services team


It should come as no surprise that the country has been thrust into a significant cold spell. Mid-February brought significant snow fall and temperatures well below zero. The silver lining — according to many — is this may reduce overwintering populations of insects for 2021, right?

Research conducted in 1993 in South Dakota and Iowa confirms prolonged cold temperatures can increase the mortality of eggs in the soil profile. The figure below shows after 18-26 days at 25 degrees Fahrenheit, we can expect to see around 24% less corn rootworms. However, according to Rutgers University, 9 inches of snow can effectively keep soil 42 degrees above the air temperature.

Low Temperature Effects on Hatch of Western Corn Rootworm Eggs (Woodson et al. 1993)

Location 30.2°F 28.4°F 26.6°F 24.8°F
Sioux Falls, SD

61 d


47 d


39 d


26 d


Correctionville, IA

60 d


44 d


31 d


18 d


With snow cover effectively insulating the soil from these cold temperatures, we can expect no immediate relief from rootworms in 2021. In fact, based on trap and rotation data, Nebraska, Kansas, Iowa and Colorado could face heavier populations due to less rotation in 2020. With the prevalence of pyrethroid-resistance, Bt-resistance, long emergence windows and more continuous corn acres, a program approach is required for 2021.

Soil-applied insecticides can have a drastic impact on our plant stand, root health, rootworm populations and yields. FMC offers several different products to protect your crop your way.

When Steward® EC insecticide is applied at a minimum of 10 fl. oz./A with a properly timed application for control of adult corn rootworm and a second application is required within 21 days due to adult corn rootworm counts exceeding one beetle per plant (determination shall be made solely by an FMC representative and/or FMC authorized agent), FMC will reimburse up to $12.00/A or the cost of a respray product(s)*, whichever is less, for a second application to manage adult corn rootworm populations.


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Always read and follow all label directions, precautions and restrictions for use. Some products may not be registered for sale or use in all states. FMC, the FMC logo and Steward are trademarks of FMC Corporation or an affiliate. ©2021 FMC Corporation. All rights reserved. 21-FMC-1849 02/21


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