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The Battle of the Knapweed - A Conservation Success Story

July 13, 2012
D'Jeane Peters, Public Affairs

In the 1970s, a neighbor asked John Adams, “Have you been getting this little purple flower? I hear it’s called Rooshan Knapweed.” The plant he was referring to is of the genus Centaurea, commonly called knapweed, an invasive plant that crowds out native grasses and decreases range health. That question was the beginning of the war on weeds for the late John Adams. His children, now owners of the ranch, still battle knapweed on their property near Big Timber, Mont.

In the 1980s, a government surveyor took one day on the ranch and mapped approximately 1,500 acres of knapweed. The topography of the ranch makes weed control difficult´┐Żlarge boulders, dense tree cover, and steep hills make spraying weeds using a truck nearly impossible. They resorted to spraying the weeds by hand. “It was like vacuuming your ranch,” says ranch owner Nina Christianson.

Ranch owners also worked with an entomologist to release Cyphocleonus achates, a weevil that utilizes the knapweed plants during its life cycle, stunting the plant’s growth and preventing its spread. This biological control helped, but the population of beetles could not keep up with the spread of the knapweed.

In 2001, ranch manager Dave Gano arranged an aerial spraying of picloram, a chemical herbicide. The aerial spraying took into account the difficult topography of the ranch, as it was able to coat areas previously only accessible on foot.

Photo of ranch manager pointing out diminished size of kanpweed.
Dave Gano, ranch manager near Big Timber, Montana, demonstrates the stunted growth of a knapweed plant. 
Photo of large knapweed plant with many purple blossoms before spraying.
An untreated knapweed plant in bloom.
Photo of dead kanpweed plant after spraying.
A large knapweed that has been sprayed with herbicide.

Gano received some help from the county weed agency, but most of the financial burden of the weed management fell on the shoulders of the ranch. “It was a back and forth battle. We’d get a good, wet year, and then the seed bank would spring back,” says Gano. The seed of the knapweed remains viable in the soil for up to five years, waiting for conditions to be right for growth. He thought he had gained an upper hand on the weeds, but when the drought broke in 2004, the weeds sprang back and Gano was discouraged. “You’d have to spray again and again.”

The county weed specialist recommended that he talk to the staff at the Natural Resources Conservation Service (NRCS) about the weed control special initiative. The ranch applied for a contract in 2005 and received financial assistance for aerial spraying, hand spraying, and the release of additional knapweed weevils. “These bugs are our hope for the future,” says Gano.

The weed control contract requires a very proactive approach to weed control. At the same time each year, Gano and an NRCS employee go out to check on designated monitoring plots. A GPS device is used to mark the location of these plots, ensuring they are located in the same place each year. Photos are taken in order to be compared each year. Gano has noticed an additional benefit to keeping such a close eye on the weeds, as it helps monitor the encroachment of any new invasive species, such as leafy spurge.

The neighbors are also taking note of their progress, since weeds pay no attention to property boundaries or fence lines. “[It’s about] getting the whole drainage to work together,” says Gano. Both ranch manager and ranch owner are grateful for their contract. “We wouldn’t have given up, but we wouldn’t have gained on the weeds,” says Christianson. Through NRCS, they have been able to afford the costs associated with stopping noxious weeds and improving their rangeland health.