The second BMP: employ two stages of defense against rootworms. For many, this means planting a hybrid with two pyramided Bt traits that protect against rootworms.
If rotation or planting a pyramided Bt hybrid are not options, Evans suggests a third BMP – using a soil- or foliar-applied insecticide in combination with a single-Bt trait hybrid.
In Gray's research, a pyramided hybrid has typically garnered better root ratings than a soil insecticide plus a single Bt trait. To date, research does not indicate that adding a soil insecticide to a pyramided hybrid, one expressing more than a single Cry protein targeting corn rootworms, makes economic sense.
Lastly, Evans urges growers to work harder at scouting for and controlling adult populations. This means getting in the field in early August and counting gravid female beetles. Those who find more than two pregnant females per plant should consider a late-season application to knock down the population for next year's growing season, he recommends.
"More than 90% of the performance-inquiry fields where best management practices were adopted in 2012 saw minimal feeding damage, and farmers who planted soybeans were able to reset the corn rootworm populations in those fields," Evans notes.
Gray says last year's test plots highlighted just how devastating an active rootworm population can be in hot and dry conditions. In DeKalb County plots, Gray and his Department of Crop Sciences colleagues, Ron Estes and Nick Tinsley, planted numerous hybrids, some with Bt rootworm protection, some without. They also applied planting-time soil insecticides to some Bt hybrids in plots and left others untreated.
The biggest yield difference cropped up between non-Bt hybrids (without a planting-time soil insecticide) and pyramided hybrids. The plot with no protection saw average root injury ratings of 2.32 (over 2 nodes of roots destroyed) with a yield of 23.2 bushels. In the same experiment, a pyramided hybrid, also without soil insecticide, had root injury ratings of only 0.33 (one-third of a node destroyed) and yielded an average of 145.4 bushels.
"You don't want to make a mistake with this insect, especially in hot and dry conditions," Gray notes.
Gray's recent surveys at the Corn and Soybean Classics suggest most folks are already protecting against rootworm resistance by planting a pyramided corn hybrid, i.e. one that includes two Bt traits to protect against rootworms.
More than 70% of the participants said they will plant a refuge-in-the-bag hybrid in 2013. Gray conducted the poll in five locations (Champaign, Malta, Moline, Peoria and Springfield). More than 550 farmers were polled. It shows this technology has caught on perhaps faster than many anticipated.