Agent Orange chemical in GM war on resistant weeds

Farmers all over the US are facing a growing challenge from weeds that are resistant to chemical sprays

Dow Agrosciences says its new GM product is based on a chemical that was once a component of the Vietnam war defoliant, Agent Orange.

It is needed they say because so called "superweeds" are now affecting up to 15 million acres of American crops.

Dow argues the new approach is safe and sustainable.

For a farmer like Jeremy Leech who grows corn and soybeans near Humboldt, Nebraska, resistant weeds are a constant threat to his farm and his family.

Last year he spent around $7,500 on chemical sprays to combat the threat to his crops.

The herbicide failed to kill the giant ragweed that had grown on his land, strangling his soybeans and his income. Worse, the pungent pollen from the towering pests exacerbated his eight year-old daughter's asthma.

"When that stuff is pollinating it makes it hard for her to breathe outside and when you live on a farm you know the kids play outside all the time and they love it and when that pollen gets really bad she gets choked up," he says.

Farming revolution

Thousands of farmers across the US now face similar problems with weeds that can withstand powerful herbicides. Scientists say it is because of the success of GM crops that were introduced in the mid 1990s.

Monsanto became a world leader in the field thanks to the introduction of Roundup-ready corn and soybeans. These crops were engineered to be able to survive spraying with glyphosate, a chemical marketed as Roundup.

Jeremy Leech has battled resistant weeds on his Nebraska farm.

Farmers just needed to use this one spray on their fields and it killed all the weeds but left the crops intact. Growers rapidly adopted the new technology as it cut their costs substantially.

"Roundup was the one that was supposed to do wonders," says Jeremy Leech's father, Van.

"And it did for the first few years; anybody could raise clean beans. Obviously over the last few years, bean fields are beginning to look more and more like this," he says, pointing to a field where weeds tower over shrunken crops.

To see how bad the weed problem can get, I travelled to an experimental plot near David City run by the University of Nebraska with Prof Stevan Knezevic.

We stand in a cornfield surrounded by towering green plants. But there is not an ear of corn in sight. The stalks that surround us are Giant Ragweed, one of the "dirty dozen" weeds that have acquired resistance to Roundup.

Harvesting corn on the Leech farm in Nebraska

So powerful have these monster weeds become become that even spraying them with 24 times the recommended dose of Roundup fails to kill them.

These plants suck the light and the life from the crops. Just one resistant weed every 10 square metres can reduce the yields from productive plants by 50%.

"Over the past 15 years I said that if we continued using roundup, roundup roundup, we're going to have a problem - now we have that problem," says Prof Knezevic.

"The reason why we are here is that we all mismanaged this technology."

Back to the future

Recognising the scale of the problem, the biotechnology industry believes that newer more effective forms of GM are the solution. Dow Agrosciences is now seeking US government approval for the Enlist weed control system.

Instead of the crop being resistant to one chemical, it is engineered to resist two. Dow says this is a more effective solution because it allows farmers to mix and match their sprays more effectively, making for a far more sustainable system.