California rice farmers face a critical production problem with no easy solution as they find that the remarkably effective herbicide Londax is losing its punch against some important weed species. "Londax gave the industry the best control of broadleaf weeds and sedges of any herbicide ever used," says Jim Hill, a UC Davis Cooperative Extension agronomist. Late in the summer of 1992, however, weeds that should have been controlled cropped up in four rice fields. The following season the same weed species showed signs of herbicide resistance in 72 fields. Last year the problem grew dramatically as more than 4,000 rice fields were affected. "It doesn't bode well for the long-term use of Londax and we don't see many alternative herbicides on the horizon," Hill says. The loss of Londax also has important water-quality ramifications because the herbicide is so compatible with California irrigation systems. Hill and the county Cooperative Extension farm advisors who work with the rice industry suggest growers adopt strategies, such as crop rotation and alternative herbicide practices, that may delay the onset of weed resistance in their fields. Their advice is summarized in a fact sheet available from the UC Davis agronomy and range science department or from Cooperative Extension offices in rice-growing counties.