Insecticide usage down, herbicides not so much after GE crops in Nebraska

Date:06-16-2011

Using genetic engineering to endow corn with protection against pesky weeds and insects was supposed to cut back on use of agricultural chemicals and the risk they pose to the environment.

But the recently released report on 2010 Agricultural Chemical Use from the National Agricultural Statistics Service carries at least one major twist on the pesticide pattern in Nebraska.

Even as use of the popular weed killer atrazine held close to the level it was at for corn in 2003, the glyphosate option more commonly known as Roundup has gone from about 1.25 million pounds in 2003 to almost 3 million pounds in 2005 and to 7.1 million pounds last year.

The major spike means more farmers have been choosing corn varieties that carry resistance to Roundup and other products with glyphosate as their active ingredient in the seed sack.

That makes them a biotechnology tool in a weed-killing approach in which the chemical can then attack both grass and broad-leaf invaders without hurting the corn.

But as McCool Junction crop consultant Bill Dunavan and other weed-wise observers in Nebraska know, Roundup has not held on to its reputation for being the only herbicide treatment farmers would need for the whole growing season.

In fact, resistance to glyphosate has been showing up in such common invaders as mare's tail, and atrazine remains a prominent second treatment in the weed arsenal to combat resistance -- and to keep more weeds from becoming resistant.

Dunavan is careful to note that atrazine -- now under special review by the Environmental Protection Agency because of cancer and other health concerns -- is in a secondary position.

In this decade, "rates have been reduced, as well as entire large farms that don't use any."

And even as the EPA has cut back maximum applications, "farmers have cut back even further."

That's not to say that atrazine is on its way out.

The 2010 report put total Nebraska pounds at about 5.5 million, down from 7 million in 1997. But atrazine use on corn was as high as 7.4 million pounds as recently as 2005.

Ben Pinkelman of Hartington, current president of the Nebraska Independent Crop Consultants, isn't surprised by those numbers.

"Insecticide use has definitely come down," Pinkelman said. "Herbicide use has shifted. We use a heck of a lot more glyphosate and less of other products."

He mentioned lambsquarter and water hemp as other common weeds in Nebraska that seem to be standing up more to the glyphosate punch.

Another reason herbicide use runs into the millions of pounds in Nebraska each year is because more farmers are using no-till and minimum-till approaches to keep soil residue in their fields, thus lessening erosion and evaporation.

Lowell Sandell, a weed science specialist at the University of Nebraska-Lincoln, said earlier claims that biotechnology would dramatically cut chemical use have not proven especially true on the weed side.

"I would suspect that the whole level, the total level of use, would be roughly similar," Sandell said. "The biggest shift has been from non-Roundup ready crops to Roundup ready crops."

The university strongly backs the idea of using more than one strategy to control weeds, he said.

Roundup is "a very good product, but with the development of glyphosate-resistant weed species, one of the things the university always tries to promote is an integrated management approach -- which is multiple effective means of action."

Randy Pryor, based in Wilber as an NU Extension educator, said Nebraska is certainly not the only place where resistant weeds are turning up. "Other states are documenting other weeds that are now truly resistant to Roundup," Pryor said.

But that shouldn't be taken to mean that atrazine eventually will be used again at the levels it was in the 1980s and 1990s.

He cited "new products on the market for pre-emerge or post-emerge weed control that are ounces per acre as opposed to pounds per acre."

Still, progress with insecticides might be easier to measure.

"We're seeing less pesticide use on insects via airplanes or ground-rig spraying." He cited more insect-resistant seed and "reduced corn borers, corn earworm and cutworm problems compared to years ago."

That's a gain for the public and for farmers, "because they're not having to handle insecticide when they plant now."