Weeds Acquiring Herbicide Resistance from Crop Rice, Study Shows

Researchers from Washington University in St. Louis sampled weedy rice, a relative of cultivated rice, from fields in Missouri, Arkansas, and Louisiana. They found that 57% of 201 samples were resistant to the imidazolinone family of herbicides. Rice growers began planting cultivars that were engineered to be herbicide-resistant, to help them manage the problem of weedy rice in their fields depressing crop yields. These cultivars were also hybrids more prone to shattering in the field, leading to more volunteer crop rice in fields throughout the year. Researchers believe this led to crosses with weedy rice that allowed the weed to “steal” the genes for herbicide resistance over the course of just a few years. Testing in Arkansas rice fields in 2018 found that 98% of weedy rice samples showed genetic markers for some level of herbicide resistance. The study’s senior author notes that problem weeds have “grabbed the best defense we’ve had against them — herbicide resistance — right from our own high-yielding rice cultivars.”