One whiff of Russian knapweed and there’s no mistaking its nasty nature. Beef cows will avoid the noxious perennial in the field, but when it’s cut and baled, they’ll eat it as readily as they would alfalfa, says David Bohnert, Oregon State University Extension beef specialist.
They’ll also maintain body condition, says USDA-ARS rangeland ecologist Roger Sheley, who, like Bohnert, is based in Burns. The researchers teamed up to study the baled weed’s palatability as part of a continuing effort to help growers beat back its invasive spread.
“We are not promoting knapweed as a crop,” emphasizes Bohnert. “Using it as a feedstuff is part of an overall management tool to hopefully get rid of it.”
Like what you're reading? Subscribe to eHay Weekly and get the latest news right to your inbox.
In Oregon and across the West, Russian knapweed flourishes where there’s subsoil moisture, especially in the corners of center-pivot-irrigated, highly productive alfalfa fields. The weed spreads by rhizomes and, somewhat, by seed, explains Sheley. Herbicide control isn’t very effective — the weed’s extensive rhizomes are hard for chemicals to reach.
“It grows really thick and really heavy, up to 1 ton/acre. There are hundreds of thousands of acres that are dominated with Russian knapweed, and much of it is useful as livestock feed,” he says.
“Russian knapweed is really tough. By cutting it prebloom, you can dramatically decrease the amount of seeds that are produced. Knapweed will try to regrow, but it is going to struggle because most soil moisture is used up. People who have Russian knapweed, especially those who have haying equipment, can bale it and then feed it as a protein supplement either on winter range or when they’re feeding low-quality hay.”
The protein content of Russian knapweed varies depending on when it is cut; young plants will contain more protein, says Bohnert. “In our study, the protein was around 13%, prebloom. I have seen reports of knapweed at 15-18% protein.”
The researchers cut and baled knapweed and fed it to gestating cows. “Ours went to the knapweed readily,” says Bohnert. “They really liked it. They were getting some pretty nasty grass-seed straw, and when we threw baled knapweed in the bunk, they went crazy with it just like alfalfa. They preferred it.”
“The animals performed exactly as if we were using alfalfa as the protein supplement,” notes Sheley. “The animals all maintained a body condition score of 5, while the cows consuming grass-seed straw without supplemental alfalfa or knapweed lost more than a full body condition score.”
Bohnert recommends against feeding the baled weed to lactating dairy cows because it may alter the flavor of their milk. He also warns that it is toxic to horses.
Growers interested in baling knapweed need first to decide if there’s enough available to justify the fuel and labor costs.
“A lot is going to depend on your infestation level,” Bohnert notes. “You are looking at $200-250/ton of alfalfa. If you could get a half ton or a ton to the acre of knapweed, it might be worthwhile.”
He warns that baled knapweed isn’t very marketable beyond the farm gate because it can readily infest fields that are free of it. It’s also a good management practice to clean equipment after baling to avoid transferring the weed to other fields, Bohnert says.