Video: Why isn't weed killer working anymore?

Farmers used to worry about weeds. Then, herbicides solved that problem. At least for a while. In 1997, there were 432 new patents for herbicides; by 2009, there were only 65.

Developing broad-spectrum glyphosate and "Roundup Ready" crops worked so well that people basically stopped looking for new herbicides.

But then the weeds started fighting back.