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CropTalk: Corn Rootworm: 2020 Reflections for 2021 Solutions

October 2020

Published on Thursday, October 1, 2020

Corn rootworm tends to be a measurable issue every year, but 2020 corn rootworm incident reports have been higher than normal. Although farmers across Beck’s marketing area experienced higher rootworm populations, northern Iowa has the most documented reports. Iowa Field Agronomists NATE MAYER AND JON CASPERS have been in the trenches, evaluating corn rootworm damage, trait integrity, and measuring beetle populations to provide proactive recommendations for 2021 success.

Why did we see higher corn rootworm feeding?

CASPERS: A perfect storm — excellent egg laying conditions last fall followed by a winter that provided sufficient snow cover to act as an insulation blanket, preventing cold temperatures from reducing egg populations. Optimal conditions for egg hatch and larval survival paired with good early planting conditions resulted in an confluence of timing that increased the potential for feeding injury. In addition tothese factors, warm nights and maxed out growing degree units (GDUs) caused an explosion in populations.

How did traits/insecticides impact corn rootworm feeding?

MAYER: High reports of corn rootworm damage yielded a lot of inspections, digs, and trait tests. When populations reach numbers like we experienced this year, it can be hard to determine whether it is a resistance issue, insecticide performance, or overwhelming pressure. The rootworm larvae must eat the root tissue to ingest the protein expressed by the trait(s) that will kill them. High populations per plant of larvae eating even one bite can cause a significant amount of damage. Dry conditions in 2020 didn’t assist our fight with corn rootworm. Dry conditions cause smaller root development, increases stress conditions which can reduce the expression of traits, and can prevent soilapplied insecticides from working to their full potential. The damage is evident, but the time needed to evaluate true resistance can be lengthy.

What concerns do you have for 2021?

CASPERS: A lack of moisture can cause significant cracking, cracks as deep as 12 in. This is important because the beetles have a head start in moving deeper into the soil, making survivability favorable for the next growing season. The depth of these cracks affect populations in two ways: first, the beetles have more favorable conditions to survive the winter and second, the deeper the beetles go, the more spread out the emergence is. Thus, the beetles are below the major root zone at a susceptible stage of the corn crop.

MAYER: Other environmental conditions that will affect the populations for 2021 are: fall moisture, frost depths, snow cover, spring moisture, soil temperatures, and accumulated GDUs. That said, there are many unknowns as to what the exact numbers are, but so far, the environment is favoring high populations in 2021. Remember, when corn rootworm is an issue, first year corn-after-corn is just as susceptible as multi-year corn-after-corn.

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Author: Nate Firle

Categories: CropTalk, 2020

Tags: CropTalk, corn, corn rootworm

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