The extremely dry weather and hot temperatures have reduced pasture growth statewide. When forage is in short supply, cattle and other animals may eat plants that they normally would avoid.
“We are seeing very low availability of good forage right now, so producers should use caution when grazing,” said John Jennings, Extension forage specialist. Plants such as perilla mint and poison hemlock are more prominent this year and are toxic to grazing livestock.
During the last week of June, there were two confirmed cattle deaths due to drought-damaged forage in Arkansas.
“Perilla mint is especially troublesome this year. It’s normally is found in shady spots along pasture borders, but has become established out in open pasture areas over the past couple of years.
“As the only green plant in some pastures, it’s poisoning hungry livestock. Perilla mint can be easily killed with herbicide, but make sure the plants are completely dead before allowing livestock access to sprayed areas.”
Hemp dogbane is another very toxic weed that is becoming more prominent, especially in hay fields.
“Many producers have cut back on herbicide and fertilizer applications, allowing this weed to become established,” said Jennings. “Plants such as perilla mint and hemp dogbane remain poisonous even in dry hay and can cause livestock poisoning when the hay is fed later in winter.”
Other plants that can be toxic include coffee senna, sesbania, and sicklepod.
“While these plants typically grow in cropland areas that are not grazed, poisonings can show up if drought affected crops infested with these weeds are salvaged by baling them for hay. That was a concern last year and will be again this year.”
Some producers are looking at any source of alternative forage, including the stalks from their sweet corn patch.
“In Clay County, stalks from sweet corn were tested and found to contain high levels of nitrate which is also toxic to livestock,” Jennings said. “Crop residues should be tested for nitrate before considering them as livestock feed.
“Confirming the crop chemicals used to grow those crops is important because many chemical labels prohibit use of treated crops for livestock feed.”
Johnsongrass is tricky, not only because it contains prussic acid when drought-stressed, but “the grass may appear normal in the morning, but can wilt during afternoon heat which increases toxic potential. Many producers believe the white powdery substance commonly seen on johnsongrass stems in late summer is prussic acid residue, but it is only common powdery mildew fungus and is not considered toxic to livestock.”
For more information on forages, visit www.uaex.edu  or contact your county Extension office.