A comparison of two herbicides from the same company shows vastly different results.
Larry Guy found two surprises in the test plots of aerially sprayed pricklypear on his ranch.
First, he noticed that one treatment was working significantly faster than the other. Second, native grass production in that treatment area increased substantially, even before the cactus was dead.
An experienced brush fighter, Guy has sprayed lots of pricklypear on his Rafter L Ranch northeast of Abilene.
Left alone, the cactus costs him valuable grazing, both through its competition for moisture and the physical barrier it presents.
Guy knows pricklypear has been notoriously slow to die — or even to show symptoms — after aerial spraying. The cactus has taken as long as three or four years to die after being sprayed with the old standard, Tordon® 22K herbicide. It could take two years for the sprayed pricklypear to start turning yellow, a sign the herbicide was working.
But in one of the test treatments, Guy was seeing yellowed pricklypear after just three or four months. Most of the pricklypear was dead within a year of application. “It is working in this first year,” he says. “It is working in all the soils.”
That treatment, Guy learned, was MezaVue™ herbicide, which became available in December 2018.
Faster signs, faster control
Early in 2016, researchers from Dow AgroSciences (now Corteva Agriscience™, Agriculture Division of DowDuPont) approached Guy about establishing test plots to compare the new pricklypear herbicide with the old standard. They were encouraged by early trials and wanted to showcase MezaVue herbicide under commercial conditions.
In April 2016, they aerially sprayed one set of plots with MezaVue at the rate of 32 ounces per acre. In another set, they sprayed Tordon 22K herbicide at the recommended rate of 32 ounces per acre. They repeated the tests in April 2017.
Guy’s results were similar to those at other sites. Across seven trials, 89 percent of pricklypear broadcast-treated with MezaVue showed significant yellowing (40 percent or more) within four months of application. Of the pricklypear treated with Tordon 22K herbicide, only 22 percent showed that level of yellowing.
As the pricklypear yellowed, Guy noted the grass response. “It is unbelievable the extra production of grass that I am seeing behind MezaVue,” he says. “I think it is almost double.”
Across 14 test sites established in 2015 and 2016, MezaVue™ herbicide also killed more pricklypear in two years. Within 24 months of broadcast spraying, MezaVue averaged 74.8 percent control. Tordon 22K averaged 65.2 percent in two years.
Symptoms provide assurance
Some of the 2015-2016 trials were established by Texas A&M researchers on the Cloud Ranch, near Albany, operated by Mark Moon. He, too, is a veteran of pricklypear control and the slow control of Tordon 22K herbicide.
In one case, Moon waited a full four years to see control from Tordon® 22K herbicide. Most of the pricklypear finally died in the fifth year after application. “I had never seen that before, but Tordon was always a really slow process,” he says.
By contrast, Moon could tell something was different in the first plots established on his ranch in 2015. One treatment stood out. At the time, Moon did not know it was MezaVue herbicide.
“It was evident from the very get-go that one of them was working quite a bit faster,” he says. “It killed a lot faster.”
In March 2016, Texas A&M researchers established another set of plots on Moon’s ranch. This time Moon knew which plot was MezaVue herbicide. Once again, its early activity on pricklypear was noticeable.
Faster symptoms provide assurance that his investment is working, Moon says. But fast control is even more important.
“Anything that you can do to speed it up and get grass production is what we are after,” he says. “That is what we do; grow grass as fast as we can.”
Window of application
Beyond quicker control, Moon noted another difference between the herbicides: the need for rainfall. Pricklypear can absorb herbicide both through its pads and its roots, if the herbicide is active in the soil. Both Tordon 22K and MezaVue herbicides are soil active. Rainfall soon after application seemed to speed the activity of Tordon 22K, Moon says. But MezaVue™ herbicide seemed less dependent on rainfall for its quick action.
“What I noticed with the MezaVue is, we did not get any rain on it, and it was already yellowing,” Moon says. “We always waited until we had plenty of chances of rainfall before we ever sprayed pricklypear [with Tordon 22K]. Maybe the rain is not as critical with MezaVue.”
More experience will be needed with the new herbicide, Moon asserts, but if rainfall is not as critical, the optimum application window gets wider. That is not a claim by the manufacturer, however.
A need for speed
The quicker activity of MezaVue herbicide comes from its combination of three active ingredients, says Dr. Charles Hart, a rangeland ecologist and market development specialist for Corteva Agriscience.
“The actives in there not only help each other, but each one does something different to get to an end result that is much faster,” Hart says. “That is what we are getting with MezaVue. We have found a quicker way to kill pricklypear and a quicker way to see activity.”
Faster control means faster grass response and a quicker return on investment, Hart says.
Pricklypear has some speed of its own. It spreads both by seed and vegetatively when fallen pads come in contact with the soil. It is such an efficient user of water that it thrives in a drought.
According to Texas A&M University, pricklypear density can increase 25 to 30 percent each year during prolonged drought, while other plants decline. At that rate, its canopy doubles every three years.
Increasing pricklypear densities can mean a significant decline in carrying capacity. Because cattle avoid the pricklypear spines, any area covered in the cactus is essentially removed from grazing.
“The choices for the rancher then are either to reduce stocking rate or to be overstocked,” Hart says. “Or increase grazable acres by controlling pricklypear. It is a very opportunistic plant that has almost no natural enemies, so it is not likely to go away by itself.”
For Wildlife, Pricklypear Can Be Too Much of a Good Thing
Dr. Dale Rollins has defended pricklypear and its role in habitat, first as a Texas A&M AgriLife Extension wildlife specialist and now as executive director of the Rolling Plains Quail Research Ranch (RPQRR) near Roby.
But in 2015 and 2017, the Quail Research Ranch hosted test plots with MezaVue™ herbicide.
“I’ve been pretty vocal in saying pricklypear is important to quail,” Rollins says.
One of Rollins’ axioms is, “Pricklypear gets too thick for ranchers before it gets too thick for hunters, before it gets too thick for cows, before it gets too thick for bird dogs, before it gets too thick for quail.”
Still true, he contends.
“But when it increases 15 to 20 percent per year, you can get too much of a good thing,” he admits.
“One of the biggest challenges we face on the Rolling Plains Quail Research Ranch is to keep pricklypear at a biologically satisfactory level and do it in a way that is not so intrusive.”
Pricklypear can provide nesting cover for quail, especially when native bunch grasses cannot because of drought. It also provides escape cover, and its fruit (tunas) serves as a food source.
Broadcast spraying of pricklypear also takes out forbs, a prime food source for quail, for at least a year or more. Given that, Rollins works to minimize spray effects beyond very narrow targets.
The RPQRR staff divides the ranch surface into “polygons” and classifies pricklypear on a 4-point scale. Zero is no pricklypear; 1 is scattered; 2 is moderate; 3 means you cannot step without hitting one. At level 3, Rollins considers broadcast spraying.
“When you have an abundance of grass with low-growing pear, grass can grow over the top of the pricklypear, and that is a minefield for bird dogs,” Rollins says.
In the tests with MezaVue, Rollins asked the helicopter pilot to spray isolated polygons of 3 to 5 acres each. Such “surgical application” did not make the biologist popular with the pilot.
“But he could do it. The technology is there,” Rollins says. “The cost of application did go up.”
Many ranchers with both wildlife and cattle enterprises recognize the tradeoffs of pricklypear control. They have found other workarounds, including individual plant treatment, spot-spraying with ground broadcast rigs or aerially spraying only parts of a pasture.
The density of pricklypear to spray and the method to use is a decision unique to each rancher, says Dr. Charles Hart, a rangeland ecologist and market development specialist with Corteva Agriscience™, the Agriculture Division of DowDuPont.
“A little bit of pear is not a bad thing. It depends on what you are doing with that property,” Hart says. “The problem is keeping pear at a low density with its unique ability to thrive and spread when environmental conditions limit the growth of more desirable plants.”
Spray decisions should rest on a rancher’s goals for the land and the comparative value of potentially competing enterprises, Hart says. Recognize that an acre of pricklypear is one less acre available to graze. When you lose enough acres, you are out of the cattle business.
“When pricklypear starts to reduce forage production to the point where it is either A, causing you to overgraze, or B, causing you to reduce your stocking rates, that is when it becomes economical to treat pricklypear,” Hart says. “A rule of thumb is anywhere above a 30 percent to 40 percent cover.”
Corteva Picks up Dow Mantle in Range and Pasture
MezaVue™ herbicide is the first new Range & Pasture product from Corteva Agriscience™, Agriculture Division of DowDuPont. The new company is a result of the 2017 merger of The Dow Chemical Company and DuPont.
The agriculture division combines the strengths of Dow AgroSciences, DuPont Pioneer and DuPont Crop Protection. In the second quarter of 2019, Corteva (pronounced kohr-TEH-vah) is expected to become an independent, publicly traded company.
All of the Range & Pasture products of Dow AgroSciences are now offered by Corteva Agriscience. MezaVue is the first of three new Range & Pasture products the new company expects to introduce over the next three years.
Pricklypear Control is excerpted from the February 2019 issue of The Cattleman magazine. Join today to start your subscription.
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