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Last updated at 12:35 BST, Thursday, 20 September 2012

American superweeds


20 September 2012

Farmers all over the US are facing a growing challenge from so-called 'superweeds' that are resistant to chemical weed killers. Because genetically-modified crops are designed to be protected from one type of weed killer, farmers have become over-reliant on using this chemical on their crops. However, some weeds have developed a natural resistance to it and are spreading rapidly. Scientists have designed a new type of GM crop which has resistance to more than one chemical, to aid farmers in killing the weeds.


Matt McGrath

A field of genetically-modified crops

What happens when weeds become resistant to weed killer?


Click to hear the report


Nebraska farmer Jeremy Leech is happy to be harvesting his corn this year. In 2011 he spent around $7,500 on herbicides that completely failed to stem the weeds strangling his crops.

To overcome the problem of resistance, Dow Agrosciences are now seeking a licence to plant a new type of GM that has resistance to Roundup, and another older chemical called 2,4-D. 2,4-D is best known as a component of Agent Orange, a defoliant sprayed extensively during the Vietnam war. But farmers like Jeremy Leech are worried that if the new GM is overused, weeds might well become resistant to it as well.

Jeremy Leach, farmer:
I think 2,4-D will work fine but I’m afraid, nervous, of what’s going to happen, four or five years down the road now if we keep using 2,4-D like we’re going to have the same problem we are now with Roundup.

Dow are likely to get the go-ahead to plant the new GM next spring. But, surprisingly, the company stresses that chemicals alone won't beat the weeds. As well as sprays, they say, growers now need to incorporate older weed control techniques often used by organic farmers.


Click to hear the vocabulary





toxic chemicals used to kill weeds

to stem

to stop or restrict


ability of an organism to protect itself


applying for

a component

a part of


chemical that removes the leaves from trees and plants


over a wide area

get the go-ahead

be allowed to start