Hoary cress displays showy, white flowers in dense clusters giving the plant the common name, "white top." The short, fine, whitish hairs that cover the 1 to 2 foot (30.5 to 61 cm) tall plant give the species its official common name, hoary. The small 4-petalled flowers are borne in flat-topped clusters at the tips of branches. The blue-green leaves are oblong, 1/2 to 3 inches (1.3 to 7.6 cm) long and smooth. They are arranged alternately on the stem. Mature leaves have a very short to no petiole , with upper leaves clasping around the stem. Lower leaves do have petioles. The 1/16 inch (1.6 mm) oval, reddish-brown seeds are found in pairs within heart-shaped pods.
This species is native to Eurasia. Because of its remarkable adaptability to different environmental conditions, including alkaline soils , it can be found all across the state, although infestations are small and scattered. It is most common in the western part of the state.
Like other creeping perennials, its root system makes hoary cress difficult to eradicate. The dark-colored roots are slender and reach 10 to 15 feet (3.1 to 4.6 m) deep, although they may grow as deep as 30 feet (9.2 m). Root buds can develop into new shoots.
Hoary cress is the earliest growing noxious weed in South Dakota. It flowers in May and becomes dormant during mid-season. The plant's aggressive nature and drought tolerance makes it a concern. Nearly all infested acreage is in pasture and rangeland. It is very seldom found in cropland. This species is most common on alkaline, disturbed soils and is highly competitive with other plants.
Spring is best for controlling hoary cress because of the plant's mid-season
dormancy. Hoary cress can be eradicated with a
combination of cultivation, planting of competitive crops, and application of chemicals.
Alkaline soil - a soil having so high a degree of alkalinity
(pH 8.5 or higher) or so high a percentage of exchangeable sodium (15 %
or more of the total exchangeable bases), or both, that plant growth is
Noxious weed - designation of the State Weed Control Board. These are weeds that are difficult to control once they are established.
Perennial - a plant that lives more than two years.
Petiole - a small stem that attaches a leaf to a branch.
Agricultural Research Service of USDA, Common Weeds of the U. S. 1971.
Dover Publications Inc. NY.
Agricultural Extension Service, South Dakota State University South Dakota Weeds, 1974. South Dakota Weed Control
Cooperative Extension Service, South Dakota State University U.S. Department of Agriculture. Noxious Weeds of South Dakota Extension Special Series 34.
Klingman Glenn C., Weed Science, 1982. John Wiley & Sons Inc. NY.
Zimdalhl, Robert L.,1989. Weeds and Words The Etymology of the Scientific names of Weeds and Crops. Iowa State University, Ames, Iowa.
Noxious Weeds of South Dakota , Extension Special Series 34, 1993. Cooperative Extension Service, SDSU, Brookings, SD 57007.
South Dakota/Nebraska Weed Identification Guide, 1994. Black
Hills RC&D Office, 515 9th Street, Rapid City, SD 57701-2663.
Leon Wrage, Extension Weed Specialist, SDSU, Brookings, SD. 1997.
Darrell Deneke, Extension IPM Program, SDSU, Brookings, SD .
Publication of the Hoary Cress fact sheet was funded by the Northern State University CUEST Center for Environmental Education, Aberdeen, SD.