By MATEUSZ PERKOWSKI
An invasive species that has traditionally been considered worthless in Western pastures is actually a useful protein source for cattle if dried and baled, experts say.
Russian knapweed, a purple-flowered broadleaf plant that invaded the West more than a century ago, possesses qualities similar to alfalfa when supplementing lower-quality feed for beef cattle, according to researchers at Oregon State University and USDA.
"What really surprised me is they would consume it at levels sufficient to maintain their body condition," said Roger Sheley, rangeland ecologist with USDA.
The results were eye-opening because cattle are usually reluctant to eat Russian knapweed when it's growing in the field, said David Bohnert, an extension beef cattle specialist with Oregon State University.
When the weed was cut and baled, however, the cows took to it as eagerly as they would to alfalfa, Bohnert said. "They went to it readily. They didn't seem to have any aversion to it at all."
Exactly why the Russian knapweed became more palatable is still a mystery, but it is possible that a "volatile" smell that it usually emits while living isn't as objectionable when the plant is dried, he said.
It's also possible that beef cattle are simply less discriminating in their tastes during the winter, when they typically consume baled feed, said Sheley.
In terms of effect on body weight, feeding Russian knapweed is equivalent to alfalfa as long as its lower level of protein is accounted for, said Bohnert.
Whereas alfalfa has about 20 percent protein, the knapweed has about 13-15 percent protein, so cattlemen can increase the amount of knapweed to make up the difference, he said.
"There are a lot of cases where it already exists and people are trying to figure out what to do with it," said Sheley. "It's one of the many ways we can begin to think about using these invasive plants."
While the researchers don't intend to promote Russian knapweed as a crop to be especially grown for forage, it's commonly found in the corners of fields that are irrigated with center pivots, they said.
In such situations, the weed should be harvested before it goes to seed to preserve its forage quality and prevent further incursions on new territory, according to Sheley and Bohnert.
"You need to be really careful where you feed it so you're not spreading it," Bohnert said.
Russian knapweed shouldn't be fed to horses, as it can cause a deadly neurological disorder, but it can otherwise be harvested and used in a fashion similar to alfalfa, they said.
Typically, an acre generates about three-quarters of a ton of the weed, which is enough to economically justify harvest -- especially with high feed prices, Sheley said.
"It's rhizomatous, so it's very thick," unlike sparser weeds that are harder to swathe, rake and bale, he said.
Chemicals alone are of limited utility against Russian knapweed, as it will typically re-invade an area unless cool season grasses can be established, they said.
Using the weed as feed can help knock it back to make herbicides more effective, Bohnert said. "If you have it, it's an alternative you can use with herbicides to get rid of it."