IN a new study from the University of Illinois, scientists document waterhemp’s resistance to yet another class of herbicides, known as Group 15s. The study provides the first documentation of a non-grass plant to be resistant to Group 15 herbicides. There are many herbicides on the market, but they all fall into one of 16 classes describing their mode of action (MOA), or specific target in the plant that the chemical attacks. Because of various regulations and biological realities, a smaller number of herbicide MOAs can be used on any given crop and the suite of weeds that goes along with it. Historically, about nine have been useful for waterhemp — and now the weed appears to be resistant to at least seven.