Weevils key to control Canadian thistleIn a privately-owned field on Dickinson’s State Avenue Friday morning, about 500 nearly-microscopic Canada thistle stem-mining weevils were released in an effort to control a widespread noxious weed.
In a privately-owned field on Dickinson’s State Avenue Friday morning, about 500 nearly-microscopic Canada thistle stem-mining weevils were released in an effort to control a widespread noxious weed.
Despite its sharp, spiky leaves and delicate purple flower, Canada thistle is not as sweet and innocent as it may appear.
“Canada thistle infests more than 1 million acres in North Dakota, recently surpassing leafy spurge as the state’s most prevalent noxious weed,” according to a Dakota West Resource, Conservation & Development Council press release.
An aggressive, creeping perennial, Canada thistle infests cropland, pasture, rangeland, roadsides and non-crop areas. Since cattle typically will not graze near infestations, Canada thistle reduces forage production and consumption, according to the release.
As part of a partnership between the Stark County Weed Board and Dakota West RC&D, a Canada thistle biological control initiative is being conducted, in which weevils will be released as a method of bio-controlling the noxious weed.
Diane Allmendinger, Stark/Dunn County weed control officer, said the weevils are host-specific, meaning they will not transfer to other plants.
Instead of spraying chemicals, biological controls are often used in areas dense with trees, where it is inconvenient to take equipment down and spray, Allmendinger said.
“If you spray this (Canada thistle) you’re not going to find it all, you’re not going to get it all,” said Jared Andrist, RC&D coordinator.
The weevils were purchased from a pest control provider in Bozeman, Mont. and all the critters will be released on private lands throughout Adams, Golden Valley, Mercer and Stark counties.
The land on State Avenue was chosen for bio-control as it has the ability to be easily monitored, but the other five sites to receive the weevils are not as easily accessible, Allmendinger said.
“People know about Canada thistle and they tend to pay attention to it,” Allmendinger said. “This (amount of Canada thistle) isn’t even shocking anymore.”
Using weevils for bio-control has been ongoing for five years and is doing well, Allmendinger said.
“They’re so expensive … what we just dropped on the ground I think was 250 bucks,” Allmendinger said. “If we could afford to put out a huge amount, it would go a lot faster.”
Andrist said not only is cost a factor, but weevil supplies are also limited.
“As more viable weevil colonies become established, it is hoped they will one day serve as collection sites to increase distribution at a lower cost,” according to the release.
The weevil’s larvae hatch on the plant’s young leaves or stem tissue, then bore into the plant and mine towards the main stem where more mature larvae mine the stem, crown and root, according to the release.
As a result, the plant’s root reserves are reduced by an average of 50 percent.
Funded through the North Dakota Resource Conservation and Development Association, the project’s price tag is about $28,000, Andrist said.