Superweeds pose GM-resistant challenge for farmers    The so-
called "superweeds" have arisen because of the success of
genetically modified crops, which now account for the vast
majority of US corn, soya and cotton.  GM essentially means that
crops are protected from one type of chemical weedkiller. But
because farmers have become over-reliant on this one product,
weeds with natural resistance have spread rapidly and have
strangled production on millions of acres.  Scientists say the
solution to the widespread resistance problem is a new type of
GM that uses a powerful weedkiller that was once part of Agent
Orange, the defoliant widely used during the Vietnam war.
Produced by the BBC's Matt McGrath and Franz Strasser.