Writer: D'Lyn Ford
LAS CRUCES -- Fire may be a good way to get rid of weeds on Texas and Oklahoma rangelands, but a New Mexico State University range scientist said the control method is not so hot for dealing with broom snakeweed in New Mexico.
"Burning should only be done under prescribed conditions, and in New Mexico the ideal weather conditions rarely occur," said Kirk McDaniel with NMSU's Agricultural Experiment Station.
Ranchers lament poisonous broom snakeweed, common on rangelands throughout New Mexico, because it chokes out grasses desirable for grazing cattle. "One of its common names is turpentine weed, and if you take a bite of it, it tastes like gasoline," McDaniel said. "Cows have the same reaction to it, so it's a plant that the animals won't eat unless they absolutely have to."
The goal of a prescribed burn is not only to reduce the amount of broom snakeweed but also to get increased growth of grasses for grazing, McDaniel said. That means rainfall is needed following a burn to promote the regrowth.
"Prescribed burning is a tool that is usually used in areas with higher rainfall, such as Texas or Oklahoma, and there's a greater fuel source available to carry the fire," he said. "New Mexico's really marginal in terms of having enough fuel and the ideal weather conditions in order to burn."
McDaniel and his graduate students conducted seven years of research at NMSU's Corona Range and Livestock Research Center, located 15 miles east of Corona, on whether prescribed burning is an effective way to control snakeweed in the state.
"We've conducted more than 100 burns," McDaniel said. "We've tried to conduct our fires in a way that we burn under a variety of weather conditions to determine the ideal air temperature, relative humidity and wind conditions necessary to control snakeweed with fire on blue grama grasslands."
The fires were started with small torches in research plots that were cleared around the edges to create fire breaks. "It's exciting research in that you never quite know what the fire is going to look like as it carries across the plot," he said.
For a prescribed burn to be successful, weather conditions must be optimum before, during and after the fire. "Landowners can control the before and during conditions, but the after conditions are obviously out of their hands," McDaniel said.
Results of the research showed that when conditions are right, prescribed burns do kill the snakeweed. "But we don't necessarily get good enough grass growth after to justify the burning expense," he said.
Part of the problem is that a year or two can go by before conditions are optimal to start a prescribed fire. For example, during the seven years of research at Corona, McDaniel said the scientists only had three years in which there was a suitable window of opportunity to burn. Even then, the window was only a few days in either the spring or summer.
"There's a lot of risk associated with this practice, because a rancher may rest a pasture a year in advance in order to get enough fuel to conduct the fire," McDaniel said. "Then the next year when they hope to burn, the air temperatures may be wrong, or the windy conditions may prevent safe conditions for starting the fire."
The rancher must then wait another year to see if conditions are right. If the fire is conducted, then the land needs to be rested a minimum of one and ideally two growing seasons after to allow grasses to come back to support grazing again.
"The rancher is looking at a big economic investment to keep the cattle off the land," McDaniel said.
Ranchers have other options for controlling snakeweed. "There are some situations in which a stand of snakeweed is too dense to burn, and the only option for removal is chemical control," he said. "In other situations, when there is a minimal amount of snakeweed, it is possible to reduce the plants' impact through grazing management."
Sometimes snakeweed becomes infested with insects like the round-headed root borer. "In this case, you want the insects to do their business and eliminate the snakeweed. You don't have to go in there with chemical control or burning," McDaniel said.
Results of the research, funded by the state and a special grant from the U.S. Department of Agriculture's Cooperative State Research Service, were published recently in the Journal of Range Management.
© 2013 New Mexico State University Board of Regents
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