Sendero herbicide tested in brush sculpting study
VERNON – Because brush invasion can reduce forage availability by two-thirds on rangeland, finding an economical control is critical, according to a Texas A&M AgriLife Research range scientist at Vernon.
Dr. Jim Ansley, AgriLife Research rangeland ecologist, has been working on brush management treatments for many years and has determined mechanical treatments to grub out mesquite are tremendously expensive, and fire can be used as a maintenance tool, but not to kill mesquite.
“We estimate that forage or livestock production can be reduced by as much as 60-70 percent because of brush invasion,” Ansley said. “It reduces forage production that much. And in particular, it affects the best grasses that cattle use in our mixed-grass region of the Southern Great Plains – the warm-season mid-grasses. That’s because mesquite and those grasses are growing at the same time.”
Ansley is working with Dow AgroSciences to study their product, Sendero herbicide, and determine how the product will work in brush sculpting for wildlife habitat, preserving secondary shrubs favorable to wildlife, while controlling mature and regrowing mesquite.
“What tends to happen when we get mesquite invasion is we maintain some grass cover, but the grass community usually shifts to the cool-season Texas wintergrass, because it is growing in the spring before mesquite trees leaf out,” Ansley said. “Once mesquite leafs out, wintergrass goes dormant – the leaves roll up to almost like strands of wire and it is very unpalatable.”
All the warm-season mid-grasses are gone because they have been outcompeted due to the shading and competitive water use by the mesquite, he said. Cool-season annual grasses like cheatgrass have the same effect as Texas winter grass on reducing the production of the warm-season mid-grasses.
Ansley said there are varying levels of effectiveness and expense, when it comes to mesquite control.
“We know fire can be used as a maintenance treatment, but it cannot reduce the density of mesquite because it does not kill many plants. Even if a severe fire is able to top-kill large mesquite trees, you won’t kill them outright and you will get resprouting. So we think one of the most viable alternatives for killing mesquite is aerial herbicide work,” he said.
In the agreement with Dow to evaluate Sendero, Ansley said the goal is to look at the product in more of a total ranch management context, “where we are spraying patches and using what we call brush sculpting to manage the whole system for the benefit of both livestock and wildlife.
“We want to knock back the mesquite and enhance the growth of the secondary shrub species for wildlife, such as lotebush, which we believe will be pretty much unaffected by this spray.”
Ansley said the Sendero treatment was applied to areas where roller chopping work was done eight to nine years ago and resprouting was occurring, as well as to areas of old-growth mesquite.
Application was made in early July using a helicopter, which provided a high degree of precision as to where the spray was applied, he said. Already sharp lines of contrast between treated and untreated areas can be seen.
Using a helicopter to spray was not that much more expensive than fixed wing: $14 per acre by helicopter versus $9 per acre by fixed-wing plane, Ansley said. That’s just the application cost; the chemical is around $20-$25 per acre.
“Sendero is designed to cause high root-kill in mesquite, so we can create clear patches of mesquite vs. mesquite-free areas in a brush sculpting mindset,” he said. “We think this provides the best opportunity for developing long-lasting vegetation diversity – both in terms of species and structurally – on a ranch that is going for multiple uses.”