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45555

Skipping Bt Traits To Cut Costs

Economics of corn production are continueing to shift, and many farmers are trying to find ways to cut input costs. One option may be planting corn hybrids without Bt protection from the European corn borer, corn rootworm, or both. While this has the potential to reduce seed costs, it could also reduce crop revenues. Before purchasing those hybrids, make sure you're not cutting corners while cutting costs by considering yield potential and insect populations.

The first thing to consider when selecting a corn hybrid is yield potential. Bt traits only provide a yield benefit when targeted insects are above economic levels, according to a report from University of Minnesota Extension integrated pest management specialist Bruce Potter, and Ken Ostlie, Extension entomologist.

“When insect pressure is low, any potential yield gains of newer, trait-protected hybrids have to be balanced against their higher costs,” the specialists say. “A more important consideration may be limited availability of high-yielding non-Bt or single Bt trait corn hybrids for much of Minnesota.”

“European corn borer populations are in general low in Minnesota and much of the Midwest and have been suppressed for several years,” according to Potter and Ostlie.  “However, they may be locally higher in areas where significant amounts of corn without Bt corn borer trait(s) were planted in 2014. Reports of slight corn borer damage in non-Bt corn demonstrate corn borers are still around but a temporary increase in non-Bt corn acreage should not dramatically increase the risk of damage. Planting corn without Bt corn borer protection should be relatively low risk. Any risk can be reduced if you scout fields and apply a labeled insecticide where needed.”

Cold temperatures and saturated soils last year may have been the cause of less lodging damage from corn rootworms. In some fields, planting corn without a Bt-RW trait in 2015 won’t result in damage, but other fields may have high populations of beetles resulting in yield loss.

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Figure 1. Western corn rootworm beetles.

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Figure 2. Northern corn rootworm beetle.

“In many cases, beetle populations did not peak until September. In general, western corn rootworm beetles (Figure 1.) are less abundant this year but fields with high populations (> 1 beetle/plant) exist,” say Potter and Ostlie. “Additionally, northern corn rootworm beetles (Figure 2.) are more numerous than they have been in the past.”

There’s a potential for a rootworm problem in 2015, even if corn didn’t lodge in 2014. Evaluate your management practices that could influence populations.

“Unless fields were well scouted for corn rootworms in 2014, some
situations should be carefully pondered,” according to Potter and
Ostlie. “Fields with hybrids maturing late for the area, fields with
portions replanted or where crop development was delayed by flooded
soils this spring, corn fields with late season weed populations or
adjacent to weedy soybeans, or soybean fields with heavy volunteer corn
should be considered at some risk from corn rootworm in 2015.”

“In Minnesota, there is minimal risk for economic damage from western corn rootworms in 2015 rotated corn,” the specialists say. “While extended diapause issues have been suppressed over the last 10 years, a few reports of economic damage in rotated corn this year and the more numerous observations of northern corn rootworms this fall should be a warning not to ignore northerns. Rotated corn may still be at risk from extended diapause northern corn rootworm.”

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