Swart also discussed herbicide trials and noted that the old standard sulfonylurea materials are no longer effective on resistant ryegrass. Axial XL and Hoelon showed typically acceptable levels of control in the Gulf ryegrass plots but mostly unacceptable control in resistant ryegrass.  “The two-step program was the best control in the study,” he said.

Swart said trials also included several combinations and options of standard herbicides, including double applications of Axial XL and stand-alone trials with Axiom. Even with two Axial XL treatments, control in resistant ryegrass was not acceptable, he said.

Axiom, at the 6-ounce rate, provided suppression of the resistant ryegrass, and higher rates, 10 ounces, tended to injure some wheat varieties. Swart said injury is mostly stunting and probably would not affect grain yield. Forage production could be reduced, however.

A new pre-emergence herbicide, Zidua, from BASF, “looks promising but might not be a stand-alone product on the resistant ryegrass,” Swart said. Registration could come as early as 2014.

Swart said wheat farmers in the area who are seeing resistant ryegrass this spring have no effective control options this late in the year. “But next year, they can incorporate the two-step program and clean them up.”