First Confirmation of Cry1F Resistant Fall Armyworm in North Carolina Corn

Fall armyworm can sometimes be confused with corn earworm.  Falls are smoothed bodied and have a square dot pattern near the end of their body.

Fall armyworm can sometimes be confused with corn earworm. Falls are smoothed bodied and have a square dot pattern near the end of their body.

The first discovery of fall armyworm in corn expressing the Cry1F toxin was made in Hyde County during August 2013.  Corn hybrids planted in North Carolina that express this toxin include Genuity SmartStax, Herculex, and Optimum Intrasect.  Both Genuity SmartStax and Optimum Intrasect also express other Bt toxins.  Widestrike cotton also expresses Cry1Ac in addition to Cry1F.  Implications that this may have in the future will be discussed in this article.

Fall armyworm is a migratory pest in North Carolina that cannot overwinter in the state.  Cry1F-resistant armyworms have been confirmed in Puerto Rico and Florida, where they likely reproduced and found their way into the state through migration.  They developed resistance because of continuous corn planting, a reminder of why planting our refuge is not only important, but required.  One reason fall armyworm is more common in the Blacklands is because this area falls within these normal migration pathways.  We do not know, from year to year, exactly when and where these moths will come from.  Migration is highly dependent on weather, with fall armyworms often being blown in by storms.  Therefore, it is not a sure bet that these resistant moths will be back in 2014, but it is a possibility.

Corn ear dropping to the ground from fall armyworm tunneling into the shank.

Corn ear dropping to the ground from fall armyworm tunneling into the shank.

Because of their migratory nature, fall armyworm is a late-season pest and is not often widespread.  Late-planted crops will be more at risk.  Thus, if a corn hybrid or cotton variety expressing the Cry1F toxin is planted, fall armyworms may not be a problem on crops expressing Cry1F, even if resistant moths are back in 2014. The field where fall armyworm was discovered in 2013 was a situation where the worms had caused a major yield loss.  Ears were dropping on the ground from tunneling in the shank and large worms were feeding on the ear.  However, surrounding fields with hybrids expressing Cry1F (both Herculex I and Optimum Intrasect) only had fall armyworms at low levels which were not economically damaging.  Finally, fall armyworms were not reported from Widestrike cotton in 2013.

With that in mind, we need to be cautious as we approach the 2014 season.  Make sure that you are informed and aware about the Bt trait package that you have planted in both cotton and corn.  If you have any suspicions of resistance, please get in touch with your county agent.  Finally, be sure to keep an eye on any late-planted crops.

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