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The one thing certain with CRW is that nothing is certain. While western CRW resistance to the Cry3Bb1 trait has been established in multiple areas within the Corn Belt, it continues to be spotty. Even in those areas, other traits appear to provide control, though the low dose rate (offers less than 99.9% control) of CRW traits, including pyramid traits, suggests resistance will eventually develop. Careful use of these tools in conjunction with integrated pest management techniques and best management practices can extend their useful life.
Crop rotation and scouting defense
Other than crop rotation, Steve Pitstick agrees with Gray on the importance of scouting, and he certainly "mixes it up." This year the Maple Park, Ill. corn and soybean grower added pyramid-stacked traits to an every-other-year rotation of the three available single CRW traits on his 2,600 acres. After running some plots in 2012, Pitstick also applied Aztec soil insecticide as a first line of defense on all single-trait hybrids except where rotating into 2012 soybean fields or in check plots in select fields. Even with two modes of action, he reports root feeding, regardless of treatment. However in the checks, lodging and root feeding were extensive. In one field where he used only a single-trait hybrid with no overlay, 25% of the field is flat.
"The rootworms just overwhelmed the traits in the checks," says Pitstick. "This was especially true in areas that were high yielding in 2012. I think those areas were more succulent and attractive last year and became a trap crop for beetles laying eggs."
He also suspects last year's beetles laid eggs deeper due to the drought, resulting in a prolonged hatch this past spring. Unlike many growers, Pitstick did not have delayed planting. As a result, later emerging larvae missed the first nodal roots with the highest expression of Bt protein. Scouting fields throughout the season, Pitstick noted feeding was primarily on later emerging, higher nodal roots with less protein expression.
Even with late season feeding, the difference between insecticide overlay with single traits and no insecticide was noticeable. "Leaving the check showed we did the right thing," says Pitstick. "You could see the difference with a significantly larger root mass where an insecticide was used. We also noticed that hybrids with a naturally large root mass were better able to handle the late feeding than those with a smaller root mass."
He warns growers where delayed planting produced late, succulent "feeding traps" this year to expect similar pressures. Noting extremely heavy adult populations feeding on his family's pumpkin patch as late as early September, Pitstick expects equally high rootworm pressure in 2014 and will continue and perhaps expand his overlay protection.
"Next year we may use an overlay with pyramid-trait hybrids too," says Pitstick. "I want the trait as backup in case it is too dry to activate the insecticide beyond the furrow so we get control outside the zone."