This bushy annual weed is a member of the goosefoot family, Amaranthaceae, that also includes beet, cockscomb, and Gomphrena. It is native to southeastern Russia and western Siberia but was introduced into the South Dakota in 1873 as a contaminant in flax seed and has spread into most of the US but causes the most problems in dry sites along the Atlantic coast, and in the western half of the country. Plants are found in areas with full sun and un-compacted soil such as overgrazed rangeland, irrigated fields, vacant lots, and roadsides but are rarely a problem in well tended landscapes.
Description: Russian thistle has a taproot up to three feet long with extensive lateral roots. Its highly branched stems grow eight to thirty six inches long and usually have reddish to purplish stripes. The stems are soft and green at first but become somewhat woody with age. The first leaves are one inch long, dark green, cylindrical and fleshy at but later leaves are stiff and short with a sharp tip. The flowers lack petals and are produced in the upper leaf axils, subtended by a pair of small spine tipped bracts. They appear from mid summer into fall and are followed by black, shiny,winged seeds that remain in the leaf axils until the plant dies, dries, breaks off at soil level, and becomes a tumbleweed, dispersing the seeds as the plant is blown about by the wind. Plants spread by seed.
Control: Mowing and pulling young plants can be effective if repeated until no more plants appear. Special care should be taken to remove plants before they set seed. Herbicides are rarely needed for control in the home landscape.
Karen Meyers