NRM researchers assisting with Huisache control efforts in South Texas
By: George Watson
All along the U.S. Gulf Coast, from Florida through the deep south and into Texas and Mexico, and all the way down to South America, grows a thorny, native plant that really has no useful agricultural purpose other than the fact that its blooms are used to make perfume.
Yet Vachellia farnesiana, commonly known as the Huisache (pronounced Wee Sach) plant, thrives and continues to exist. If left untreated, the bush can actually grow to be the size of a tree, roughly 30-40 feet tall. The plant, however, is becoming more dense along the coast and also is migrating northward in Texas, reaching as far north as Waco, according to Robert Cox, an associate professor in Texas Tech's Department of Natural Resources Management.
The changes create an issue for ranchers in South Texas who have to battle the invasive plant. Its prevalence has reduced grazing land for cattle, and efforts to eradicate the plant on ranchlands have proven either ineffective or very expensive due to the mixture of chemicals that are sprayed.
"It is difficult to control," Cox said. "It re-sprouts if you cut it off. If you try to grub it out, a lot of times you'll leave buds behind and those sprout out. They've even applied herbicides that have not been very successful. Sometimes if you apply it aerially or by helicopter, you get a pretty good kill, and sometimes you get almost no kill. So it's hard to predict what will get a good kill."
From those frustrations, ranchers in South Texas reached out to Cox and a pair of students in the Department of Natural Resources Management to determine if certain methods used to control Huisache – not eliminate it completely, but just limit its effect of taking over ranchland – are effective enough to apply for federal funding that could control the tree.
Cox, along with doctoral student Chris Miller and graduate student Courtney Jasik, will spend the next three years monitoring Huisache control efforts, sprearheaded by the Coastal Prairie Grazing Lands Cooperative (GLC). The GLC will spray a designated area of ranchland where Huisache is growing, then researchers at Texas Tech will collect and analyze the data to determine whether the less-expensive mix of chemicals is effective in at least limiting the spread of the tree.
"One of the biggest problems ranchers have is invasive species like Huisache and the cost of treating the species," Miller said. "So when I saw this project to help ranchers find a better and cheaper way to treat an invasive species, I was all for it. Just knowing that this research will help fellow ranchers in the future brings joy to me."
The way this research is being conducted is unique in that it is the industry performing tests and asking academia to interpret the results. Usually, it is researchers performing the tests and determining conclusions, then offering results to the industry for use. This project also gives students an outstanding opportunity to make an impact through working directly with industry leaders.
"Working on this project will give me a better understanding of the land and vegetation in this area, as well as a broader view of different land management methods and ways to help landowners meet their goals," said Jasik, who intends to pursue a career in rangeland management after earning her master's degree.
Battling Huisache. The roots, so to speak, of this project go back a few years to when Cox and retired Texas Tech professor Ron Sosebee met with landowners in South Texas. The landowners were troubled by Huisache, which has been invading grazed pastures and was moving north and west toward the Big Bend region.
The plant itself is not harmful to livestock if ingested, but it is a nuisance due to its ability to quickly overtake large portions of ranchland. As it spreads, the amount of forage produced decreases, and Huisache eventually becomes dense enough that cattle find it difficult to move through a ranchland to find available grazing.
As Cox and Sosebee began meeting with the landowners, former Texas Tech doctoral student Pablo Teveni, who recently earned his doctorate, began investigating the role of carbohydrates within the Huisache plant. They theorized that when the Huisache begins moving carbohydrates and sugars out of the leaves and into the roots, it also would move a sprayed herbicide out of the leaves and into the roots.
For three years, Cox said, Teveni traveled to sites around Victoria, Refugio, Goliad and near Kingsville on the King Ranch each month to dig up a series of Huisache trees and test the roots for carbohydrate content. At the same time, researchers would spray a series of Huisache to test his theory. Cox said Teveni identified a window in the late spring and in late September/early October where herbicide could be applied and it would be relocated from the leaves to the roots with the carbohydrates and kill the plant.
As part of that research, Cox, Sosebee and Teveni met twice a year with area landowners to answer their questions and concerns and receive their input for the project. These landowners worked in cooperation with an organization called the Grazing Lands Conservation Initiative – which eventually became the GLC – along with the Natural Resources Conservation Service.
The only drawback to Teveni's approach of killing the Huisache is that the mix of chemicals used is very expensive. The best potential result was to get an 80 to 90 percent kill percentage.
"That project ended, but then about a year and a half ago, I was approached by the same group of folks saying that, building on Pablo's work, they had been thinking of new ways to treat Huisache," Cox said. "They were more concerned about getting a response in forage production. So rather than using the expensive mix of chemicals the companies recommend, this group settled on a pretty inexpensive mix of chemicals.
"By doing that, they don't care if they kill the Huisache shrubs or not, but what they are trying to do is weaken the shrubs enough that the grass on these ranchlands can respond and produce more forage for grazing. By their estimates, they can go from producing 1,500 pounds per acre of grazing forage, which is low, to up around 7,000 pounds per acre of forage, which is terrific."
Winning the Fight. With this new method, there are ways ranchers can apply for federal or state funding to help reduce the cost of treating Huisache. To qualify for that funding, ranchers must agree to treat Huisache in a way the state or federal government recognizes as effective, and their current method of treatment does not meet that qualification.
The GLC reached out to Texas Tech to collect data from spraying to verify its effectiveness so ranchers in South Texas can apply for funding. Texas Tech researchers are confident this collaboration will be successful regardless of the results.
"Whether or not this project is successful in attaining federal funding, the research that is conducted will give ranchers, landowners and rangeland managers more information and a better understanding of the methods to control Huisache and increase forage production in the Gulf Coast Prairie region," Jasik said.
If successful, ranchers may finally have the upper hand on this aggressive species of invasive plant life.
"If this method of treating Huisache is effective, then I see in the long term more Huisache-infested land will be treated, because this method could be more economically feasible," Miller said. "This would allow ranchers and other agencies to restore the Coastal Plains back to a grassland and allow ranchers to run more cattle and gain more profit per acre of land they own."
If Texas Tech researchers' analysis of the spraying proves the techniques are successful in controlling Huisache, it could have an impact worldwide.
Because of the tremendous fragrance of Huisache flowers, the plant was imported to Europe to be used in the perfume trade. Perfume companies have Huisache plantations in Portugal and Southern France, but it has become an invasive species not only in those countries but also in places like Australia and Fiji.
For Texas Tech researchers, the focus is helping ranchers in South Texas increase the forage production of their lands while also discovering control methods that could potentially lead to applications beyond Huisache. There are other factors to consider beyond whether the Huisache is eliminated, such as the effects on soil chemistry and whether the species composition and nutrition of the forage is affected.
"There are always factors that can influence success, such as weather, but I think, overall, it will be effective," Jasik said. "This method was created by different ranchers and land managers who are constantly paying attention to the land and always trying to find new ways to improve their land and increase efficiency and production. I think this treatment method has been thoroughly thought out and will be successful."
CONTACT: Mark Wallace, Chairman, Department of Natural Resources Management, Texas Tech University at (806) 742-2841 or firstname.lastname@example.org
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