The Canadian “Bt” Corn Trait Tables for 2024 are now available:
English: Canadian Bt Corn Trait Table for April 2024
French: Maïs exprimant des protéines insecticides disponibles au Canada (Avril 2024)
Bt is in quotes because RNAi (RNA interference) technology, which is not a Bt trait, is now offered in some of the packages for rootworm protection. Plants with RNAi tech produce fragments of RNA that interfere with a gene (Dvsnf7) that produces of an important protein in the gut of rootworm larvae. Without that protein, the larvae slowly die. However, the RNAi tech needs to be paired or pyramided with Bt proteins that the rootworm populations are not already tolerant to. Otherwise, resistance to RNAi can develop very quickly.
Those considering just switching to RNAi tech to solve their resistant rootworm issues need to implement other rootworm management strategies first. If your rootworm populations have developed resistance to any of the Bt proteins that are used in your “go to” hybrid packages, pairing RNAi tech with those same ineffective Bt proteins will place all the burden on the RNAi tech to provide protection. Rootworm will be able to rapidly develop resistance to RNAi in the absence of other effective modes of action against it.
Instead, consider rotating the problem field out of corn for one year to knock back rootworm populations. Applying biocontrol nematodes in the non-corn year can give the nematodes a year or two to build up in numbers to be ready to help knock back any rootworm that return once corn is back in that field for a few years. First year corn doesn’t require rootworm protection, as not enough eggs (if any) were laid in the non-corn year. So by rotating out of corn for one year, and applying biocontrol nematodes, the field won’t build to levels needing rootworm protection until at least the second, more likely third year of corn. Monitor adult rootworm populations in the first, second and third years of corn using sticky traps to know how quickly the adult populations are building. Free traps are available, thanks to GFO and ABSTC as part of the Corn Rootworm Trap Network. If traps reach 2 or more beetles per trap per day, then the next years corn crop needs rootworm protection. Targeting Bt or Bt+RNAi hybrids for the third year of corn will reduce the risk of resistance. Especially if followed again by rotating out of corn by the fourth year. Switching up the tactics used against rootworm (rotation, biocontrol nematodes, and limiting Bt or Bt+RNAi hybrids for the high risk third year) will delay resistance development and prolong the effectiveness of the few rootworm traits we have left.
Rootworm is not the only pest that is developing resistance to Bt corn. Additional reports of unexpected injury or confirmed resistance of European corn borer in Canada and the US are included in the trait tables. European corn borer populations resistant to Cry1F were found in New Brunswick, Manitoba and Quebec in recent years. In 2023, unexpected injury by ECB to Cry1Ab and Cry1A.105 was found in a field near Truro, Nova Scotia and on plants containing Cry1Ab, Cry1A.105 and Cry2Ab near New Haven, Connecticut. We will be ramping up ECB monitoring and research to determine the extent of this resistance and find ways to mitigate or delay the spread of these populations.
Regardless of the target pest, growers should avoid repeated use of the same management tool every year to reduce the risk of resistance. Implement sustainable best management practices and scout and report any injury found by pests that should be controlled by the Bt or Bt+RNAi hybrids being used. If injury has been found, contact your seed agronomist, provincial entomologist and/or Tracey Baute, OMAFRA, Chair of the Canadian Corn Pest Coalition.
For information on which hybrids or products have obtained EU approval, visit the Canadian Seed Trade Association’s corn hybrid database at: https://seeds-canada.ca/corn-hybrid-database/
More information on resistance management can be found at the Canadian Corn Pest Coalition and Manage Resistance Now websites.
Any edits or questions can be sent to Tracey Baute, OMAFRA and Chair of the Canadian Corn Pest Coalition.