True Armyworms in Corn

Angus Catchot, Extension Entomologist
By Angus Catchot, Extension Entomologist, Whitney Crow, Don Cook, Research Entomologist and Jeff Gore, Research and Extension Entomologist April 9, 2020 07:34

True Armyworms in Corn

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We have gotten numerous calls over the last week about true armyworms in seedling corn. Although this is not extremely unusual, the widespread occurrence of high true armyworm numbers across the southern region in wheat and corn (and grass in general) is not as common of an occurrence. Many have reported high numbers moving off ditch banks or other grassy areas after a burndown into corn in the V1-V2 growth stage. In at least one instance in Mississippi, they completely defoliated a stand of V1 corn (RR only).

Bt corn will have an effect on true armyworms, however, many of these worms are moving into the crop as large late instars. These later instar larvae can tolerate the Bt better, which may result in high levels of defoliation. While defoliation may appear alarming on very small corn, yield loss associated even with high levels is likely near zero on very small corn (based on work done by others assessing hail damage on seedling corn). In a study by a former graduate student of our looking at impact of fall armyworm defoliation on yield of seedling corn, at the V3 growth stage 65% average defoliation had no impact on yield as well. We did not look at V1 or V2 stage defoliation in those trials.

The growing point does not emerge until about the V5 growth stage so the corn will continue to grow despite the extreme defoliation (however, it will be slightly delayed). In the event you have a furrow that has not sealed well, it is possible they may move into the opening, chewing the stem below the soil surface resulting in a much greater issue. If treatment is needed, true armyworms are easy to control with pyrethroids. Just remember to keep an eye on your fields.

Special thanks to our consultants and retailers for providing pictures

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Angus Catchot, Extension Entomologist
By Angus Catchot, Extension Entomologist, Whitney Crow, Don Cook, Research Entomologist and Jeff Gore, Research and Extension Entomologist April 9, 2020 07:34
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