A growing problem

摘要

Palmer pigweed (Amaranthus palmeri) is not a weed to trifle with. It can reach more than 2.5 metres tall, grow more than 6 centimetres a day, produce 600,000 seeds and has a tough, woody stem that can wreck farm equipment that tries to uproot it. It is also becoming more and more resistant to the popular herbicide glyphosate. The first such resistant population was confirmed in 2005 in a cotton field in Georgia, and the plant now plagues farmers in at least 23 US states. It is just one of many resistant weeds marching through the world. The US Environmental Protection Agency (EPA) is trying to learn from the pigweed experience, and wants to limit the damage caused by the latest wave of weed control. It deserves credit and support. There is broad agreement that the spread of these resistant plants has its roots in the widespread adoption of crops engineered to be resistant to glyphosate. By the time these genetically engineered crops were released in the mid-1990s, farmers had been battling herbicide-resistant weeds for decades. But glyphosate was thought to be a particularly challenging herbicide for weeds to overcome. Few cases of resistance had been seen.