AgriLife Extension helps test new mesquite control herbicide

Texas AgriLife Extension Service range specialists have been working with Dow AgroSciences LLC since 2007 on a joint project to develop a new herbicide mix for mesquite control.

The result of the AgriLife Extension-led study is Sendero herbicide (active ingredients: aminopyralid + clopyralid) from Dow AgroSciences. The company is calling the product the "new standard for mesquite control in Texas,” said Dr. Charles Hart of Stephenville, Texas A&M University associate department head for ecosystem science and management and an AgriLife Extension range specialist.

The recommended use rate of Sendero at 28 ounces per acre has been approved through the Herbicide Use Committee as an official recommendation from AgriLife Extension and Texas AgriLife Research, Hart said.

The AgriLife Extension Herbicide Use Committee approves Texas herbicide recommendations for rangeland weed and brush control used by AgriLife Extension and the U.S. Department of Agriculture Natural Resources Conservation Service, he said.

The chemical comes with a high, 56-75 percent, control rating and is approved for use in the Natural Resources Conservation Service Environmental Quality Incentives Program brush control program as a broadcast application on mesquite, Hart said.

Timing for mesquite control has not changed with this new herbicide, and everything that applies to the old standard of the Reclaim/Remedy Ultra mix also applies to Sendero, he said.

Two important points, Hart said, are that it is approved only for a broadcast application rate at this time, and it will not be used as a basal bark or stem application as the product will not mix with diesel or basal bark oils.

"We are still working on rates for individual plant foliar treatment,” he said.

AgriLife Extension’s study, which involved five range specialists across Texas, looked at varying rates and mixes of three herbicides: clopyralid, triclopyr and aminopyralid, Hart said. Fourteen different herbicide treatments were evaluated with a total of 164 aerial plots, each 10 acres in size, over the period of 2007-2011 as part of this study.

All treatments were made in June or July at 4-5 gallons per acre total spray volume and applied by either helicopter or airplane, he said.

In 2009, the mixture of aminopyralid plus clopyralid at a 1:4.6 ratio, which is the formula for what is now Sendero herbicide, was first evaluated and has proven to be effective at controlling mesquite in annual trials conducted through 2011, Hart said.

"The new mixture showed higher average mortality and more consistent control across sites during the study,” he said.

Across three years and 14 sites, apparent mortality of mesquite averaged 66 percent one year after treatment on plots treated with 0.61 pounds active ingredient per acre of the new herbicide, compared to 57 percent on plots treated with the current standard of 0.25 pounds active ingredient per acre of Reclaim plus 0.25 pounds active ingredient per acre of Remedy Ultra.

After two years post-treatment, Sendero plots averaged 77 percent apparent mortality compared to 60 percent for the Reclaim/Remedy Ultra on all but 2011 treated plots, which are yet to be evaluated two years after treatment, Hart said.

He said the new herbicide has several advantages including: “one jug” premix herbicide for mesquite, no tank mixing of herbicides required; the product is non-restricted use, meaning a pesticide license is not needed to purchase or apply; no livestock grazing restrictions associated with the product; and it appears to be very specific to mesquite, leaving desirable shrubs unharmed.

Hart said those with questions or comments regarding Sendero herbicide can contact one of the AgriLife Extension range specialists located around the state.