The Enemy: Russian Knapweed (Acroptilon repens) is an invader from southern Russia and Asia. It spreads both by seeds and shoots. It can produce from 6 to 27 roots shoots per square foot, and roots may grow to a depth of 23 feet. This knapweed does not spread by wind as with the other knapweeds (Spotted, Diffuse, Squarrose, and Yellow star thistle). Once the white or blueish-pink, flowers are pollinated the seed head will close up and remain closed until they fall onto the soil surface and are opened up by disturbance (may be years before this happens).
The Strategy: Russian knapweed causes chewing disease in horses and can grow under a wide range of environmental conditions. Russian knapweed can be found is about every county in eastern Idaho. It seems to follow Interstate 15 from Sage Junction to Blackfoot and if you get onto any ditch or canal you are liable to find some growing along the banks.
The Defense: Controlling Russian knapweed can be a great challenge. Because these plants spread by shoots (rhizomes) controlling it by mechanical means (hand pulling, shovel, plow, disk, etc) is fairly useless. There are numerous flower and root eating insects that can be released to assist in controlling the weed in sensitive and remote areas. Herbicides seem to be the best tool in our tool box for this weed species. Herbicides such as Curtail®, Redeem®, Transline®, Milestone®, and Telar DF® are the best ones to use. The best overall control of Russian knapweed is to prevent the weed from become invasive in the first place. Healthy pieces of land will keep most weeds from getting started, but once the do, get help and get active in controlling them. As always consult with your local pest control professional or call your county Weed Superintendent for further details.
PLEASE NOTE – The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.