COLLEGE STATION – One plant currently flowering across different parts of the state is poisonous and should be of concern to ranchers, according to a Texas A&M AgriLife Extension Service expert.
Small-headed sneezeweed, which falls in the sunflower family, is a native, warm-season annual that grows statewide except for the East Texas Piney Woods and extends into northern Mexico, said Dr. Barron Rector, AgriLife Extension range specialist in College Station.
“Be aware that small-headed sneezeweed is very poisonous in the flowering stage to mainly sheep, but cattle, goats, mules and horses are also susceptible,” Rector said.
Dr. Cat Barr, Texas A&M Veterinary Medical Diagnostic Lab’s toxicologist in College Station, agreed.
“I was taught this plant causes ‘spewing sickness,’” Barr said. “Ruminants technically regurgitate from abomasum backward into the rumen, but this plant irritates the gastrointestinal tract so much that even cattle will vomit plant material and have green slobber and nasal discharge. You can imagine how a horse would colic, as well.”
Sneezeweed consumption by grazing animals produces signs of illness including weakness, staggering, diarrhea, vomiting, salivation, bloating, groaning and grinding of teeth, sticky non-pelleted feces and gastroenteritis, Rector said. Poisoned animals can have forced and fast respiration and a nasal discharge.
Signs of illness will appear within a few hours after the consumption of sneezeweed, and animals may convulse prior to death, Barr said.
“Not much else causes an illness that looks like this,” she said, “but if you need confirmation, our laboratory can examine the rumen content or stomach content microscopically and identify the plant material. We’re here to assist your veterinarian with a diagnosis.”
Rector said earlier feeding studies with this plant have shown that consumption of as little as one-quarter of a percent of an animal’s body weight produced acute poisoning and death, with the mature plants being more toxic than the seedlings.
The plant, also commonly called “small sneezeweed” and “sneezeweed,” commonly occurs in small localized areas on moist habitats of silty, clay loam and sandy soils around ponds, tanks, bar ditches and especially in ephemeral or dry creek bottoms, he said.
Rector said wet falls followed by wet springs usually assure a good crop of seedlings. He said in the past two weeks he’s seen a lot of the plants growing from Sonora to Wichita Falls.
“This spring, the small-headed sneezeweed can be found growing abundantly in creek bottoms that are drying out from Junction and Sonora northward to the Rolling Plains,” he said.
The plants have a single basal stem that can grow to a height of about 4 feet. The plant is characterized by having stem leaves that are alternate, lanceolate or oblong and are decurrent, running down the somewhat angled stem.
“Generally these plants flower in June and July but with a warm winter and spring, they are flowering in mid-May,” Rector said. “The heads have disk flower or central flowers that are tinged pale red to brown. The ray flowers are short and always yellow in color.”
Because the plants are usually found in localized areas in a pasture, hand pulling, mowing or burning may be effective management options, he said. Fencing livestock away from localized infected areas also can reduce or eliminate potential problems.
Small-headed sneezeweed is susceptible to most broadleaf herbicides recommended for rangeland use. As an annual plant, the most effective treatment with a herbicide is when the plants are 4-6 inches in height and these may be treated with ground broadcast applications before flowering when the plants are actively growing.
Rector said most grazing animals will not eat sneezeweed unless they are in a state of hunger or searching for green material or forage under conditions when grasses have matured and are in short supply.
“Your management and observation are needed to keep this plant from becoming your next problem,” he said. “It is a good idea to scout areas where you have seen this plant growing in previous years.”
Rector said additional information can be found in the AgriLife Extension publication B-6105, “Toxic Plants of Texas: Integrated Management Strategies to Prevent Livestock Losses,” found through the AgriLife Bookstore at https://www.agrilifebookstore.org/.