By Darren Hefty

It wasn’t too many years ago when Brian and I were talking on Ag PhD about how incredibly awesome it was going to be to have corn rootworm resistant Bt hybrids available.  We thought they would take the market by storm, and they have.  Sure, there was a little sticker shock to begin with, but we’ve never seen a better tool for fighting corn rootworms.  Insecticides were pretty good, often killing 80% to even 90% of the rootworms that came close to our corn roots.  The new Bt’s were close to 100%.  What an improvement!

Well, after a few short years of bliss, single trait corn rootworm Bt’s are starting to fall apart in numerous areas across the country.  The stacked trait with 2 corn rootworm genes, SmartStax, is still holding up just fine.  Not every hybrid out there is SmartStax, though.  There are new stacked corn rootworm Bt traits coming soon from other seed providers, but they won’t be out for this year.  So what’s your plan for protecting your corn plants, your yields, and your bottom line?

First of all, don’t worry about corn rootworms.  Oh, they WILL try to rob your yields, and they ARE a serious pest.  Worrying is a waste of time, though.  Instead, take action.  Here are some things you can do this year to fight back against Bt rootworm resistance on your farm:

  1. Rotate crops.  Corn rootworms are obviously not a concern in soybean fields, so go back to your normal rotation rather than planting corn every year.
  2. Control volunteer corn in soybeans.  Planting soybeans is not going to help you as much if you let volunteer corn live in your fields.  Corn rootworms can use volunteer corn as a host crop from late May to June or early July.  That’s long enough for them to complete the larvae portion of their life cycle and emerge from the ground as adult beetles ready to lay eggs for your next crop.
  3. Use a corn rootworm Bt hybrid.  Obviously it would be best if you could find a SmartStax hybrid that fits your soils and your geography.  However, if you can’t find the right genetics to maximize yield in a SmartStax hybrid, I’d still recommend using a single trait corn rootworm Bt product to at least control some of the rootworms in your field.
  4. Use a soil insecticide at planting time.  Here are some qualifiers:
    1. SmartStax corn – We’re using a half rate of insecticide on our farm to try to kill some of the rootworms before they take a bite out of our roots.  With all Bt traits, the insect has to actually take a bite out of the plant in order to ingest the Bt.  Keep in mind that the Bt protein is safe for humans and livestock, but insects are unable to digest it.
    2. Single trait corn rootworm hybrids – We’ll be using a full rate of a planting time insecticide whenever we’re planting a single trait rootworm hybrid now.  We’ve seen consistent yield improvement on our farm by doing this, and university data from your area will support it, as well.
    3. Non-rootworm traited hybrids – Yes, there’s still a place for hybrids without a corn rootworm Bt trait, like refuge areas for starters.  In this case, you for sure will need a full rate of a planting time insecticide, and you may consider a stronger than normal rate of a seed treatment insecticide, as well.  Note: the seed treatment insecticides are not great on corn rootworms.  They are merely good.  So by using a soil insecticide plus the seed treatment insecticide, you are taking two shots at the rootworms, giving you the best chance at success.
  5. Spray foliar insecticide applications as needed to control adult corn rootworm beetles.  This goes for any crop you raise because corn rootworm beetles move to soybean fields and other crops, too.

Corn rootworms are a serious problem for corn production and especially continuous corn production.  There are rootworms that have become resistant to single trait corn rootworm Bt’s.  Use crop rotation to your advantage.  Use SmartStax products where possible.  Use soil insecticides on every corn acre.  Spray foliar insecticides when needed to control adult beetles, and you’ll protect your yields and your bottom line.