“It's a thick, nasty rosebush on steroids.” That's how Mark Renz, University of Wisconsin-Madison weed scientist, describes multiflora rose. He says it's the No. 1 pasture weed in southern and southwestern Wisconsin and is a big problem in several other states, too.
Researchers estimate that over 45 million acres in the East, South and Midwest are infested. The plant can grow to a height and diameter over 10' and produce up to half a million long-lasting seeds per year.
The thorny perennial was intentionally introduced to the U.S. from Japan in the 1940s.
“It was believed that the plant would be beneficial for wildlife, but research has shown that it has actually made their habitats worse,” says Renz.
The good news is that multiflora rose can be controlled with aggressive measures used over two or more years. “We've access to a wide range of control strategies, including herbicidal, mechanical and biological methods, plus grazing,” he says.
For large-scale infestations, use herbicides first, he advises.
“Foliar, cut-stump, soil and basal bark applications can be used. Of those methods, foliar treatments are usually the most cost-effective.”
Herbicides he recommends for foliar treatments include glyphosate, Cimarron and Crossbow. “Multiflora rose is a perennial, so you're not going to get rid of it with just one application,” says Renz, who cautions users to follow label directions carefully.
For mechanical control, dig or grub out individual plants below the root crown, or mow. West Virginia researchers found that three to six mowings/year for two to three years were required to achieve good control. Renz recommends mowing when the plants are actively growing.
“Allow the buds to come out in spring, mow the plants as close to the ground as possible, let them resprout and mow again.”
Multiflora rose has a few natural enemies, including rose seed chalcid, a bug that feeds on the seeds, and rose rosette disease, a virus thought to be spread by mites.
“Once plants get infected, they die within two to five years,” says Renz. “It's a disease that's native to North America, but it has a patchy appearance. You might see it in one pasture, but not the one across the road.”
Grazing also works. “Grazing 8-10 goats/acre early in the season is very effective. Unfortunately, cattle don't feed on it, so they're not recommended as a management tool.”
Growers wanting help in identifying problem weeds should dial in to the Virginia Tech Weed Identification Guide found at ipm.ppws.vt.edu/weedindex.htm.
The online guide not only allows growers to look up weeds they may know, it also provides a grass weed identification key. By answering a series of questions about an unknown grass sample, this identification key will narrow down growers' choices and provide the identity of an unknown grass sample, according to the site.
Extension bulletins on weed control are also available on the site.