Weed Threatens Livestock

By Pam Smith
DTN Progressive Farmer Crops Technology Editor

DECATUR, Ill. (DTN) -- Don't let your livestock eat these daisies. That yellow flower popping up in hay and wheat fields is actually a weed called cressleaf groundsel that can poison livestock.

Ohio State University weed specialist Mark Loux said the weed is being found in fairly high numbers in his state this year thanks to a mild winter.

Sometimes called butterweed, the winter annual often springs up in no-till corn and soybean fields. Burndown herbicides are typically used to control it early in the spring when the plants are smaller and more susceptible, but that's not an option in forage and wheat crops.

Native to the United States, butterweed can be found from Texas east to Florida, northward along the Atlantic coast to Virginia, and west to Nebraska. The plant is poisonous to grazing animals such as cattle, horses, goats, sheep and to humans, Loux said.

There are several weeds that send out yellow flowers this time of year, said Aaron Hager, University of Illinois weed scientist. "Growers should take the time to look because wild mustard and yellow rocket can sometimes be mistaken for butterweed," he told DTN.

Close up, butterweed is easy to distinguish because it has daisy-like petals with a pincushion-like center. It is a member of the aster family. Leaves alternate on the stem, are deeply divided and lobed. Lobes have round serrated margins. Stems are hollow and grooved with purplish streaks. Most plants have one stem, but there may be more.

Loux's release on the topic said applying herbicides to hay fields now won't reduce the risk of toxicity in animals. It's also too late for wheat growers to apply any herbicide to their wheat crops."

How much of the weed it takes to harm livestock has not been well documented, Hager said. The plants contain compounds called pyrrolizidine alkaloids (PAs). The PAs are found in the plant throughout the growing season but appear to be at their highest levels when the plant is in the bud-to-flower stage.

"Drying or ensiling the plants during the hay or straw making process doesn't reduce the toxicity of cressleaf groundsel," Loux said.

Loux recommended that producers should avoid harvesting areas of the field that have high concentrations of cressleaf groundsel.

Mowing before the weed is in the bud to flower stage will most effectively prevent seed production, but that doesn't minimize the risk of poisoning. Loux stressed that it's important to prevent including those mowed plants in hay or straw -- or to discard bales that contain it. The groundsel is not likely to regrow after the first cutting of hay in the spring. The goal of control strategies should be to prevent it from contaminating the first cutting.

Hager said his research has shown that up to 98% of cressleaf groundsel plants emerge in the fall. "It's easy to control with fall or early spring burndown in crop field settings and you'll be taking care of marestail problems at the same time," he noted. "We haven't seen big problems in hayfields yet, but it's certainly something to be watching for."

Consider managing wheat and forage crops this fall too, said Loux. "There are some herbicide options in wheat and some forage crops, that can be applied in fall or early spring, but they aren't 'burndown' herbicides like glyphosate or 2,4-D of course," he said.

More information on cressleaf groundsel, including how to identify it and manage it, can be found on Ohio State's weed science website at http://bit.ly/….

Find a video about butterweed from Aaron Hager here: http://bit.ly/….

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on Twitter @PamSmithDTN

(AG/SK)

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