Surveys of Mississippi rice growers indicate that nearly 40 percent believe they have herbicide-resistant barnyardgrass in their fields, says Jason Bond.

In screening of barnyardgrass samples from 2007-2009, “we found 45 percent were resistant to propanil, 20 percent to Facet, and 15 percent with multiple resistance to propanil and Facet,” he said at the annual Delta Ag Expo at Cleveland, Miss.

“This does not mean that 45 percent of barnyardgrass in the Mississippi Delta is propanil resistant — it just means that these are the percentages we’ve observed in the samples we’ve collected, all of which came from problem fields.”

Bond, who is associate research professor at the Delta Research and Extension Center, Stoneville, Miss., says control of barnyardgrass with Clincher herbicide is “variable, from 58 percent to 97 percent in greenouse studies,” and that resistance is suspected for Newpath, Beyond, and Grasp.

“About seven to eight years after a new herbicide comes out, we usually find resistance somewhere.”

Over the years, Bond says, as growers have widely adopted Roundup Ready and Clearfield production systems, many have paid less attention to timing of herbicide applications.

“Timing is important; herbicides work better on small weeds than large ones every time. In one study at Stoneville last year, for each day herbicide application was delayed beyond optimum the yield loss was 2.4 bushels.”

For best results with barnyardgrass, Bond says, growers should start with clean fields, and “treat early and often,” using Command, Facet, Prowl H20, RiceBeaux, along with Newpath in Clearfield rice.