Species specifics: Russian knapweed

Fast facts about Russian knapweed

Deep-rooted perennial that spreads aggressively through creeping roots
Cold-hardy, noxious weed prevalent across the western and central United States
Toxic to horses, causing serious health issues if consumed

What to look for

Russian knapweed (Acroptilon repens) is an herbaceous perennial with erect stems that typically range from 18 to 36 inches tall and branch into clusters in the canopy. Lower leaves measure two to four inches long and are deeply lobed, while the upper leaves are smaller with smooth margins, though they may be slightly lobed. Both shoots and leaves are covered with dense gray hairs. Flowers may be pink, lavender or white and produce seeds that set in the fall that can remain viable for several years.

One way to distinguish Russian knapweed from spotted knapweed is by its smaller flowers, which lack the black mottling on the flower bracts found on spotted knapweed.

The deep-rooted perennial spreads aggressively through creeping horizontal roots that remain active into early winter and resumes growth as soon as soil temperatures rise above freezing in the spring. Roots have a brown to black, scaly appearance that are often visible near the crown. Because of its winter hardiness, Russian knapweed can invade and dominate sites when desirable forages are dormant or still recovering.

Russian knapweed produces a toxic compound that suppresses the growth of other plants, chewing disease, often leading to a cascade of physical and neurological issues at high doses. Livestock, including cattle and sheep generally avoid the plant or show no apparent signs of toxicity.

Where it is found

Russian knapweed is a nonnative invasive weed introduced to the western United States in the late 1800s. It has since been classified as noxious or restricted in many states and is commonly found in pastures and rangelands across the western and central United States.

How to treat it

Apply herbicides when plants are in the early bud to flowering stage during spring and summer. Fall applications can also be made to dormant plants.

Recommended treatment options:

Apply 16 to 20 fluid ounces of DuraCor® herbicide per acre, or
Apply 20 to 32 fluid ounces of GrazonPD3™ herbicide per acre, or
Apply 1.5 to 2.1 pints of GrazonNext® HL herbicide per acre

GrazonPD3™ is a Restricted Use Pesticide. GrazonPD3 is not registered for sale or use in all states. GrazonPD3 is not for sale, distribution or use in Nassau and Suffolk Counties in New York State. Under normal field conditions DuraCor® is non-volatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor to manure and urine from animals that have consumed treated forage. DuraCor is not registered for sale or use in all states. White clover and annual lespedeza exhibit some initial injury (such as lodging and loss of vigor) but recover. GrazonNext® HL has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with GrazonNext HL and to manure and urine from animals that have consumed treated forage. Consult the label for full details. GrazonNext HL is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. GrazonNext HL is not for sale, distribution, or use in New York State and San Luis Valley of Colorado. Always read and follow label directions.