A controversial new biotech corn developed by Dow AgroSciences will be delayed at least another year as the company awaits regulatory approval amid opposition from farmers, consumers and public health officials.

Officials of Dow Chemical's agricultural arm said Friday they now expect the first sales of Enlist for planting in 2014. Previously officials had set the 2013 planting season as a target, but U.S. farmers are already buying seed for planting this spring, and Dow has yet to secure U.S. approval for Enlist.

Dow has wanted to roll out Enlist corn, followed by Enlist soybeans in 2015 and then cotton, to be used in combination with its new Enlist herbicide that combines the weed-killers 2,4-D and glyphosate. The Enlist crops are genetically altered to tolerate treatments of the Enlist herbicide mixture.

The hope is that Enlist will wipe out an explosion of crop-choking weeds that have become resistant to glyphosate alone.

Opponents have bombarded Dow and U.S. regulators with an array of concerns about Enlist, which is intended to replace Monsanto's successful Roundup Ready system. Genetically altered Roundup Ready corn and soybeans now dominate the U.S. corn and soybean market.

But as Roundup Ready crops have gained popularity, millions of acres of weeds have developed resistance to Roundup herbicide, causing farmers to use higher quantities of Roundup and other herbicides to try to beat back the weeds.

Critics have said adding more herbicides to already resistant weed populations will only expand and accelerate weed resistance. Some have likened the problem to a "chemical arms race" across farm country.

"Weed resistance to chemical herbicides is one of the biggest problems farmers now face, and that is a direct result of converting so much of our farmland to herbicide-resistant GE (genetically engineered) crops," said Marcia Ishii-Eiteman, senior scientist at Pesticide Action Network.

Earlier this month, Kansas State University scientists said they have found evidence that some more weed types have developed resistance to glyphosate. Researchers said they sprayed two common weed types, waterhemp and Palmer amaranth, with up to four times the typical field use for glyphosate and the weeds would not die.

Next month the Weed Science Society of America will examine the weed resistance problems at a meeting in Baltimore.

Furthermore, several medical and public health professionals have sent a letter to the U.S. Department of Agriculture warning of health threats that could accompany an increase in 2,4-D use.

But Dow officials said Friday that its product is needed soon as market research shows that cropland acres infested with glyphosate-resistant weeds increased 80 per cent over the past two years.

As it awaits regulatory approval, Dow said it would showcase the Enlist system in five technology centres established in the U.S. Midwest and U.S. South to train farmers and seed sellers on Enlist's application and management. It also said it will offer more than 100 small Enlist field plots at seed company and retail locations and it is hoping to also set up on-farm "experience plots" to demonstrate the product.

Dow said it plans on receiving U.S. regulatory approval this year and will "ramp up" seed production and its supply of Enlist herbicide to support commercial sales starting in late 2013 for 2014 planting.

Canada granted regulatory approval in October for Enlist corn and soybeans; approvals are also being sought in Brazil and Argentina.

"We are committed to introducing this technology responsibly and sustaining it for the long term," Dow AgroSciences U.S. commercial leader Damon Palmer said in a statement.

Critics said they hoped the U.S. Department of Agriculture and Environmental Protection Agency are taking a hard look at the potential problems associated with Enlist.

"Those of us who have concerns about this are all kind of holding our breath... wondering one way or other what is going to happen with this," said Doug Gurian-Sherman, senior scientist in the food and environment program with the Union of Concerned Scientists.

Many also worry that the new biotech crops will contaminate conventional and organic crops. "There are just some huge questions that Enlist and some of these other crops have," he said.

Related stories:
Dow's 2,4-D-tolerant corn, soy traits get federal approval, Oct. 25, 2012
Alta. fields host Prairies' first glyphosate-resistant weed, Jan. 11, 2012
2,4-D-tolerant Canadian corn, soy a few years away, March 4, 2011