Hoary Cress (Cardaria draba)

Hoary cress, also known as whitetop, is a member of the Mustard family, and was probably introduced from Europe in alfalfa seed. It is a creeping perennial, which reproduces by seed and creeping roots. The extensive root system spreads horizontally and vertically with frequent shoots arising from the rootstock. It grows erect from 10 to 18 inches high and has a gray-white colored leaf. The flowers are white and numerous in compact flattop clusters which give the plant its name. Hoary cress is one of the earliest perennial weeds to emerge in the spring, producing flowers in May or June. It grows in waste places, cultivated fields, and pastures, and is capable of vigorous growth.

Comments: Limited populations in Pitkin County.

Biological controls: None currently available.

Chemical controls: For additional information contact your local city, county or town natural resource office. (See section VII for phone numbers.)

Cultural controls: Mowing or cultivation effectiveness will be increased if other plants like perennial native grasses or alfalfa are seeded in the hoary cress stand as competitors. Maintain range and pasture in good condition. Promote healthy grass growth through proper irrigation and fertilization. Do not overgraze.

Mechanical controls: Removal of top growth is somewhat effective. Repeated treatments may reduce seed production and spread.

Locations of Infestations of Hoary Cress on Roads and Open Space in Pitkin County: