THE ISSUE:  Russian knapweed   

  Russian Knapweed (Rhaponticum repens) is a creeping perennial native to Eurasia. It was introduced into the U.S. as a contaminate in seed. It is an extremely invasive weed that can infest large areas and spread quickly. It can reproduce from seed and from root buds. Its presence reduces rangeland quality as it out competes native vegetation. It has been known to cause chewing disease in horses.  It invades roadsides, pastures, rangeland, ditch banks, and other
disturbed sites.  

Russian Knapweed can grow up to 3 feet tall and is covered with wooly gray hair, giving the plant a blueish green appearance. Lower leaves are 2-4 inches in length and lobed. Upper leaves are smaller and linear, or lance shaped. Flowers can be pink, white, or lavender and are typically 1/4 -1/2 inch in diameter. They have rounded bracts that have pointed paper-like edges. The overall shape of the flower head resembles a vase. Russian Knapweed has a creeping root system, allowing it to spread and take over areas quickly. Seeds are often transported by birds, rodents, wind, and humans (on clothing
and vehicles). 

Integrated Pest Management (IPM) Options: 

• Prevention— Learn to identify this plant. Never transport unknown plant material. Clean clothing, pets, and vehicles of plant debris when leaving infested areas. 

• Mechanical— Mechanical control methods like mowing and tillage are not usually recommended as it can cause further invasion.

• Cultural— Plant beneficial perennial plants that will compete with weed seedlings. Manage plant populations in a way that will benefit beneficial plants. 

• Chemical— There are several herbicide options available to use on this weed species. For more information on products and rates visit: https://pnwhandbooks.org/weed. Then search “Knapweeds”.  Always read and follow herbicide label directions!

Justin Hatch, University of Idaho Extension Agriculture Educator in Caribou County. 208-547-3205
[email protected]