Figure 1. True armyworm feeding on wheat beards. Courtesy: Christopher Nelson
We have received quite a few reports of true armyworm caterpillars being an issue in Northern South Dakota wheat. These insects are capable of causing a lot of defoliation during the growing season. Furthermore, they will also clip heads when wheat is ready for harvest. The threshold for true armyworms in wheat is 2 caterpillars per square yard. However, if the caterpillars are feeding on the beards, developing seeds, or clipping the heads off the plants, they should be treated immediately. For more information on how to identify true armyworms, please refer to this article.
Insecticides for use in wheat can be found in the 2018 Wheat Pest Management Guide.
Table 1 contains a list of insecticides labeled for true armyworm management in wheat. Remember to double-check pre-harvest intervals to ensure that harvest is not greatly delayed by the insecticide being used.
Table 1. Insecticides for true armyworm management in wheat.*
|5-18 fl oz||7 days for harvest 30 days for straw|
|Coragen or Prevathon
|2-20 fl oz||1 day|
|1.3-3.9 fl oz||14 days|
|Mustang or Mustang Maxx
|1.28-4.3 fl oz||14 days|
*This is list is not comprehensive. Insecticides that are listed were chosen based on having pre-harvest intervals of 14 or less days.