By MINDY POEHL | Central Texas Edition

Farmers and ranchers are busy identifying toxic plants that are specific to Central Texas, at a Toxic Plant Management Workshop held in Stephenville. The farmers and ranchers learned about the damage that toxic plants can cause to livestock. — Photo by Robert Scott, Erath County Extension agent

May 4, 2006 - Many acres of Texas’ rangeland contain plants that contain compounds that are toxic to livestock. When the toxic plants are eaten, they can cause lower reproduction rates, increased supplemental feeding or even death for grazing animals, which result in economic losses for ranchers.

On Tuesday, April 25, a workshop that focused on toxic plant management was held in Stephenville. Dr. Charles Hart, Extension range specialist, spoke about poisonous plants and was on hand to help producers identify specific plants and problem areas on their ranches.

In Texas, over 100 plant species are toxic to livestock. Among them, butterweed is a cool-season annual that usually grows to 18 to 20 inches tall. The basal leaves, up to 4 inches long, are deeply lobed, with oblong, lateral lobes having wavy margins. Although the plant usually has one stalk, it occasionally has a few. It can be unbranched or branched, depending upon moisture and soil fertility. Numerous yellow flowers stand on short stalks, forming a large terminal cluster.

“Butterweed may be found in many areas of Texas, but large populations are usually present only in the eastern third of the state,” explained Hart. “It is often found in clay or heavy loam soils in disturbed areas, stream bottoms, ditches and flood plains.” 

These plants contain pyrrolizidine alkaloids that cause progressive liver cirrhosis. Consumption of large amounts of the plant can result in acute liver necrosis. However, in most instances several months elapse between consumption and the appearance of clinical signs. Horses, cattle and llamas have died of liver cirrhosis after being on pastures containing butterweed. 

“Sometimes, the toxic plant causes sudden death when horses are placed on almost pure butterweed paddocks with no hay or feed,” Hart said. 

Signs of poisoning, which are all related to loss of liver function and can include anorexia, depression, weight loss, aggression and death.

Llamas may be more sensitive to the pyrrolizidine alkaloids or less discriminating in their eating habits. Sheep are more resistant to pyrrolizidine alkaloid poisoning and may be used to “clean” the pastures while the plants are young. Severe infestations may be controlled with broadleaf herbicides.

Horse nettle is another toxic plant that is a coarse, branching perennial that grows to 1 to 3 feet high. It has spines on the stem and leaves. The oval leaves have several large teeth or shallow lobes on each side, with microscopic hairs on the underside. 

“It has pale violet to white flowers and gives rise to spherical fruit,” explained Hart. “The fruit is green with light green vertical bands until maturity, when it becomes uniformly yellow.”

Horsenettle is distributed across the eastern part of Texas and the entire eastern half of the United States. It may be found mostly in sandy soils in fields, open woodlands and waste places.

It contains varying amounts of glycoalkaloids and calystegines in all parts of the plant. The highest concentrations are in the ripe fruits. Low-level intake of calystegines over several months is probably responsible for “Crazy Cow Syndrome,” a nervous condition.

Hart said the clinical signs of cattle with the “Crazy Cow Syndrome” include: loss of equilibrium after rapid movement; extension of head and front legs; rapid eye movement; and spontaneous but temporary recovery after rest.

“Affected animals do not return to normal,” Hart said. “The poisoning itself is not fatal, but animals die as a result of accidents, particularly by drowning when water is nearby. 

Because this plant often grows in fields, take care to prevent baling fruiting plants into hay. When the plant is in round bales, cattle should not be forced to clean up the leavings, where most of the seeds will accumulate. Do not allow the same animals to continuously graze pastures containing many western horse nettle plants, especially in the fall and winter. Rotating cattle every 30 days from this type pasture to one containing few western horse nettles has helped prevent “Crazy Cow Syndrome.” Chemical control strategies include 0.6 to 0.9 pound a.i./acre of Grazon P+D as a broad-cast treatment or a 1 percent solution as an individual plant treatment when plants begin to flower in the spring.

Other toxic plants discussed at the workshop were Silverleaf nightshade, Oleandrin, Twinleaf senna, and Lantana. For more information on toxic plants, visit the  toxic plant of texas website at http://texnat.tamu.edu/cmplants/toxic/index.htm.