Determination of accase tolerance in Italian ryegrass ( Lolium multiflorum) in Northeast Texas

Northeast Texas wheat producers have observed that pinoxaden, recommended for controlling ryegrass in winter wheat (Triticum aestivum), is not effective. The Hunt county (feral) ryegrass seed was collected from a local producer with ryegrass control problems. The winter wheat was cleaned for feral ryegrass, and Gulf ryegrass was used as a comparison.;A factorial experiment was set in a randomized complete block design with four replications. The growth stages evaluated were two-three leaf and two-three tiller. Diclofop, pinoxaden, and mesosulfuron-methyl herbicides were used for confirmation of tolerance. The herbicides were applied at four rates: 1/2x 1x, 2x, and 4x of the labeled rates.;The feral ecotype exhibited tolerance to all rates to pinoxaden with 25% control two weeks after treatment (WAT) at the 4x rate. Feral ryegrass expressed tolerance to diclofop with 14% control at two WAT at the 2x and 4x rate. The feral ecotype expressed tolerance through all rates of pinoxaden with 12-17% control at six WAT. Pinoxaden at the 4x rate controlled the feral ecotype 28% at 8 WAT compared to the 100% control in the susceptible ryegrass ecotype. The feral ecotype eight WAT was controlled 12-17% with mesosulfuron-methyl compared to the susceptible ecotype control of 49-75%. Mesosulfuron-methyl reduced wet weight (Wwt) in the feral ecotype 13-37% at the 1/2x to 4x rates compared to the susceptible ecotype reduction of 54-82% at the same rates. The feral ryegrass Wwt reductions of 7% at the 4x rate of diclofop while the susceptible ecotype Wwt reduction of 77%. Pinoxaden reduced the feral ecotype Wwt 13% at the 1x rate compared to the susceptible ecotype 87% reduction. The feral ecotype dry weight (Dwt) reductions of 19-31% with mesosulfuron-methyl at the 1/2x-4x rates had less control compared to the susceptible ecotype with 63-81% Dwt reduction. Diclofop reduced the feral ecotype Dwt 0-20% with a 50-75% Wwt reduction in the susceptible ecotype. Pinoxaden reduced the feral ecotype Dwt 60-73% at 2x-4x rates when the 1/2x-1x rates reduction was 0-20% compared to the susceptible ecotype with 86% reduction at all rates.