(DTN) - Ken Ostlie fears he may have seen the "tip of the iceberg" in Bt corn rootworm trait failure.

During the recent 2010 Commodity Classic, Ostlie, a University of Minnesota Extension entomologist, discussed fields of surprise rootworm damage to Bt corn seen during the 2009 season. One of the early images in his presentation was an aerial photo of a corn field in southern Minnesota. The image was striped with thin bands of lighter green that bordered broad swathes of dark.

The thin bands, Ostlie explained to a sparse crowd of farmers and seed industry representatives, were the outside four rows of a planter pass. Those thin bands of rows were the grower's refuge corn, a hybrid without a rootworm trait that was treated with a soil insecticide. The 20 rows in between were a triple-stack hybrid, which should not be damaged by rootworm feeding, he said.

"The reason you can pick out those four (refuge) rows, is that they're standing. The 20 rows of triple-stack are not." He paused to let the statement hang in the air like a poised hammer.

Ostlie said there were pockets of damage to corn carrying a corn rootworm (CRW) trait across southern Minnesota, Iowa, Wisconsin and in South Dakota in 2009. He stressed that pest experts had yet to point any definitive fingers at reasons that those fields were damaged. Yet he peppered his comments with the ongoing issue of farmers not fully complying with corn rootworm refuge requirements. Entomologists have been warning for several seasons that the lack of adequate refuge could lead -- some say will lead -- to rootworms becoming resistant to Bt traits.

"Are we dealing with resistance, are we seeing a problem with (Bt) protein expression in that hybrid, or are we seeing some complication from the unusual weather we had in 2009? I don't know. But the real question is, if you were the farmer that had this field, what are you going to do in 2010?"

While a National Corn Growers Association news release lauded the fact that plantings of Insect Resistance Management refuges had "remained stable through the period 2007 through 2009," that stability means as much as 30 percent of farmers are not planting an adequate refuge. Official numbers, from the consortium of seed trait companies charged by the Environmental Protection Agency with stewarding Bt refuge compliance, are based on surveys of corn farmers. Some seed dealers say the lack of refuge is significantly higher in areas with heavy rootworm pressure.

Even with adequate refuge, stopping rootworm resistance to Bt traits isn't a sure thing, Ostlie said. The field he highlighted had refuge. But it, and many other problem fields, were in their fifth or sixth season of continuous corn, with continuous use of the same Bt trait, whether the Monsanto VT trait or the Herculex rootworm trait from Dow AgroSciences.

Ostlie said a Missouri study showed a 12-fold increase in beetle survival after just six generations of insects were exposed to one Bt rootworm trait.

Other reasons for the corn damage are possible, he said. Poor fertility or other stresses on the damaged corn field which could have reduced the amount of Bt protein the plants expressed. Research has shown that volunteer corn plants from the previous season's CRW Bt corn expressed lower amounts of the Bt protein that the parent hybrid. "The only thing we know that's different between a corn field and a soybean field is that most growers don't put nitrogen on soybeans. So could low nitrogen fertility cause low protein expression?"

Bill Hendrix, biology team leader for Dow AgroSciences, told DTN after the presentation that the company has not seen issues of Bt protein expression under low nitrogen or other stresses. He's also unsure of what could be happening in those problem fields.

"Nobody knows if these are resistance issues or not. There are a lot of different scenarios possible in each of those fields."

Part of the problem could simply be the way Bt rootworm traits work, Ostlie said. Unlike the "high-dose" toxin produced by Bt traits aimed at the European Corn Borer, toxins produced by Bt traits developed for rootworm are "low-dose" proteins, the equivalent of a reduced rate of insecticide. Years of crop production have shown that reduced rates can lead to earlier formation of pest resistance, whether that pest is a weed, a disease or an insect.

"And many of these corn areas have incredible amounts of larvae present," Ostlie said. "Even adding an insecticide over the top of the trait only gives us slightly more control. We still have a lot of beetles surviving."

The seed industry hopes that new SmartStax hybrids, which have two types of Bt toxins against rootworm in the stack, and a lower, 5 percent refuge requirement, will increase the number of farmers planting refuge. Ostlie has been uncertain of that, noting that the biggest issue in refuge planting is the hassle of switching seed in the planter. "That hassle is there whether it's for 20 percent or for 5 percent of the field," he told DTN.

Both Dow and Monsanto also have submitted plans to the EPA to create "refuge in a bag,"(RIB) or a mix of Bt and non-Bt seed in the same seed container. "RIB would guarantee compliance 100 percent," Hendrix said.

Such a system would help, Ostlie said. "But the RIB idea also puts the Bt and non-Bt seed closer together for larvae to move back and forth." An insect could get enough of a dose of Bt toxin to move on, but not enough to die, then survive feeding on roots of a nearby non-Bt plant.

"Right now the big debate in EPA is how much of a refuge to allow," in an RIB mix, Ostlie said. Seed companies have said farmers wouldn't notice damaged plants with a 5 percent refuge seed level scattered out across a field. With a 20 percent rate of intermixed non-Bt seed, any damage would be much more noticeable, to the eye and to the combine yield monitor.

Ostlie also told the crowd he worries that if resistance develops before the RIB idea is approved, likely for the 2012 season and then with no guarantee farmers would pay for the expected higher cost of RIB seed, it may be too little too late.

"If we actually have resistance or tolerance to one of the traits in that (SmartStax) hybrid, then everything that's stacked with that trait is only going to be slightly more effective" than one trait alone, he said.

Greg Horstmeier can be reached at greg.horstmeier@telventdtn.com.

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