Toxic Weed Invading Florida Horse Pastures

Toxic Weed Invading Florida Horse Pastures

Creeping indigo was once studied for its potential as a livestock feed, but can be deadly to horses.

Photo: Bob Peterson/Wikimedia Commons

A weed once studied for its potential as a livestock feed is sickening Florida horses and threatening to invade pastures along that state's border with Georgia.

In the 1930s University of Florida scientists began studying trailing indigo, also known as creeping indigo, for its potential as a nutrient-rich, easy-to-cultivate plant that had potential as forage for livestock, said Rob MacKay, BVSc, PhD, Dipl. ACVIM, a professor of large animal medicine at the University of Florida, in Gainesville. The researchers’ investigation ultimately revealed that creeping indigo was toxic to horses and other livestock, so they abandoned their studies into the plant.

“It became a problem when, somehow, the plant was introduced into the wild,” MacKay said.

Over the past 10 years, creeping indigo began to show up in southern Florida pastures. Since then, the plant has traveled northward to invade pastures in central parts of the state including Ocala, where some horses have become sick after eating the toxic vegetation.

MacKay said horses that consume the weed can display clinical signs including ulcers on the lips, tongue, and gums, as well as neurologic signs including blindness, staggering, and weakness.

Consumption of 20 pounds or more of the weed can be fatal for horses, MacKay said. Still, some horses actually seek out the vegetation when it's present in their pastures. “Like other toxic plants, horses can acquire a taste for it,” he added.

Some owners regularly inspect their pastures for the weed, looking for its reddish flowers and green trailing foliage. Others rely on university extension specialists in their counties to inspect pastures for creeping indigo. But even when it’s identified, the toxic weed has proven tough to kill, MacKay said.

“Creeping indigo has a long taproot that needs to be pulled out completely,” he said. “Also, it grows under other plants so it's sometimes hard to find.”

What's more, there is no commercially available herbicide recommended to permanently eradicate creeping indigo, MacKay said. The University of Florida Pasture Weed Identification and Control website suggests spraying either Milestone or GrazonNext HL, both of which contain aminopyralid. Retreatment the following year will likely be necessary, the website said, and owners should be sure to follow all label directions whenever they use any pesticide.

Owners who do find and remove the weed from their pastures should burn clippings to avoid spreading seeds and take care not to spread manure that could contain seeds that horses have already ingested. “Even the manure can be dangerous,” MacKay said.

Some horse owners in northern Florida have reported the presence of creeping indigo in their pastures, but so far, weed has not yet spread outside the state, MacKay said.

“It hasn't reached the border with Georgia yet, but we're watching where it goes,” MacKay said.

About the Author

Pat Raia

Pat Raia is a veteran journalist who enjoys covering equine welfare, industry, and news. In her spare time, she enjoys riding her Tennessee Walking Horse, Sonny.

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