Text: Kay Burdette
Photos: Janice Tucker
Russian knapweed - Acroptilon repens - is a long-lived, persistent, perennial weed that chokes out desirable vegetation. It is listed as a “noxious weed” by 18 states, including New Mexico. Russian knapweed is native to the southern Ukraine, southeast Russia, Iran, Kazakhstan and Mongolia and was originally brought to the United States (early 20th century) in shipments of alfalfa seed from Turkestan. Long-distance transport is typically as a contaminant in hay or seed lots. Russian knapweed is now widely established as an undesirable plant in the western United States, as well as in Australia where it is commonly known as hardseed.
The Santa Fe Botanical Garden first identified the plant as a problem at the Leonora Curtin Wetland Preserve in 2000. Treatment was originally applied as part of the 319 Clean Water Act in 2003-4. Currently, three to four acres with spotty to widespread growth exhibit the noxious weed. The largest area is on the south (more arid) side of the Preserve in the upland area.
The key to Russian knapweed control is to stress the weed, causing it to expend nutrient stored in its root system. The plant reproduces by seed, although the seeds are too heavy to be wind-borne. Plants spread locally via lateral extension of the roots. The weed forms dense, single species stands over time due to competition and allelopathy (biochemicals produced that inhibit the growth of other plants). Roots from a recently established plant expand rapidly and may cover up to 12 square yards in two growing seasons.
Environmental agencies (U.S. Fish and Wildlife Service and New Mexico Department of Agriculture) recommend using an environmentally safe herbicide, approved for wetlands. Treatment should be applied after the first light freeze and before the first heavy freeze. This treatment must be repeated when foliage begins to show in spring. Generally, two to three years are required for eradication.
After thorough investigation regarding the most effective and environmentally safe procedures, SFBG began treating Russian knapweed at the Leonora Curtin Wetland Preserve in late October, to be followed by an early-spring application. A wetlands approved specialty herbicide was applied using a backpack-hand sprayer in order to localize the application as much as possible. Fortunately the Preserve’s grasses appear to be strong and healthy and no reseeding of treated areas will be necessary. (Rocky Mountain Pool and Agriculture in Albuquerque has donated a portion of the herbicide.)
Funding for this project will be covered by a previous grant from U.S. Fish and Wildlife Service. We anticipate a two to three-year effort that will include crafting a comprehensive Preserve weed management plan.
Summary Facts:
Russian knapweed is a noxious creeping perennial that reproduces from seed and vegetative root buds. It crowds out other desirable vegetation. It is poisonous to horses and can cause welts and surface irritation on humans.
Russian knapweed emerges in early spring, bolts in May to June, and flowers through the summer into fall.
The key to Russian knapweed control is to stress the weed and cause it to expend nutrient stores in its root system.
SFBG will begin a two-part treatment in late October leading (we hope) to eradication of Russian knapweed at the Leonora Curtin Wetland Preserve. The second segment will occur in early spring.
