Contrary to what some people believe, it is surprisingly common for folks to graze cattle and other livestock on Johnsongrass. To many this productive plant provides high quality “free” forage. But of course, there is always the risk of prussic acid (or cyanide, HCN) poisoning. There are many ranchers here in DeWitt County that graze cattle on Johnsongrass each year. Most understand the dangers of prussic acid once we get into the hot dry summer months, and in the fall when first frost occurs. I do occasionally get reports of ranchers losing a few head of cattle to prussic acid poisoning. I also get many phone calls each year with questions related to grazing Johnsongrass and the potential for prussic acid.
Dr. Megan Clayton, AgriLife Extension range specialist, Uvalde, notes “From my experience, cattle love Johnsongrass. It's just a problem during those specific conditions during the year. If I get a call from someone wanting to control Johnsongrass, they either do not have cattle or it's in a hay field. I see an abundance of Johnsongrass in the roadside ditches, but it won't be up in the adjacent pasture because it's been grazed out.”
Dr. Clayton further notes ranchers who still have a good amount of Johnsongrass in their grazing pastures will just move the cattle when the growing and weather conditions have more potential for it to be poisonous (suddenly dry, frost, etc.)
AgriLife extension forage specialist Dr. Vanessa Corriher-Olson, Overton, seconds Dr. Clayton’s comments. “Most questions I get about Johnsongrass are how to control it, especially in a hay meadow.
A few producers that graze Johnsongrass have learned how to manage their herd to reduce any risk.”
Although many ranchers deliberately graze Johnsongrass, most probably do not want to take the risk and do everything possible to eliminate it from their pastures. Those cautious ranchers are most likely heavily influenced by all the precautions AgriLife Extension have known and recommended for decades, regarding the risks of grazing Johnsongrass as well as sorghum/ sudan, grain sorghum stubble, etc.
However, in contrast, there’s at least two regional state Extension agencies that have published guidelines for those who do choose to graze Johnsongrass: “Making the Most out of Grazing Johnsongrass,” University of Arkansas (2019).
“Johnsongrass in Pastures: Weed or Forage?,” Oklahoma State University (2017). If you would like a copy of these publications, contact the Extension Office.
The bottom line for grazing Johnsongrass in Texas is to be very cautious. I can’t say that we in AgriLife Extension would or should recommend the practice, however many local and statewide ranchers have already made this a practice and seem to understand the risks. So, in short, if you are considering grazing Johnsongrass and would like more information on how to manage the risks, contact the DeWitt County AgriLife Extension Office at 361-275-0816.
This article was adapted from a paper written in September 2024 by Calvin Trostle, Texas A&M AgriLife Extension Agronomist in Lubbock, Texas.
