Hoary Cress

Cardaria draba

What is it?

Hoary Cress (Cardaria draba), commonly known as whitetop, is a creeping perennial that is a member of the mustard family and native to Europe. The stems, in the rosette stage, may grow up to 2 inches in height and produce grayish-green leaves that are lance shaped. The leaves are alternate and 3/4 to 4 inches long. The upper leaves have 2 lobes that clasp the stem. The plant has numerous small, white flowers with 4 petals on stalks radiating from a stem. Seed capsules are heart-shaped with two small, flat, reddish brown seeds. One plant can produce from 1,200 to 4,800 seeds. The plants emerge in early spring with stems emerging from the center of each rosette in late April. Hoary cress flowers from May to June and plants set seed by mid-summer (CSU, 08/08).

Why is it a problem?

Habitats for Hoary Cress include: fields, waste places, meadows, pastures, croplands and along roadsides. It is typically found on unshaded, generally open areas of disturbed ground. It generally does better with moderate amounts of precipitation and grows well on alkaline soils (CSU, 08/08).

This plant is in the mustard family and a creeping deep-rooted perennial. This plant is considered very aggressive and eliminates other vegetation (A.Wayne Cooley, Colorado State University Extension, 1999). This weed is considered unpalatable to livestock (Curtis R. Swift, Copyright 2006-2012).

This perennial is also invasive in New Mexico.

Management Techniques:

The key to effective control of Hoary Cress is prevention: Preventing the encroachment of these weeds is the most cost-effective management. Preventing invasions by limiting seed dispersal, monitoring and using weed free hay, and quarantine animals that may have grazed in infested areas; beyond prevention, the key is early detection when infestations are small and aggressive management (CSU, 08/08).

Hoary cress is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be; eradicated, contained, or suppressed depending on the local infestations. For more information visit www.colorado.gov/ag/csd and click on the Noxious Weed Management Program. Or call the State Weed Coordinator at the Colorado Department of Agriculture, Conservation Services Division, (303)-239-4100.
Prevent the establishment of new infestations by minimizing disturbance and seed dispersal, eliminating seed production and maintaining healthy native communities. Contact your local Natural Resources Conservation Service or seed mix recommendations. Planting competitive legumes, such as alfalfa, can reduce Hoary cress in crop rotations (CSU, 08/08).
Mowing several times before the plants bolt stresses Hoary Cress and forces the plant to use nutrient reserves stored in the root system. Combining mowing with herbicides will further enhance control of this weed. Mow repeatedly during the summer, and then apply an herbicide in the fall (CSU, 08/08).

No single treatment provides effective, long term control. The best and first defense is always prevention. Once established, integrate a variety of combinations of competitive planting, crop rotations, and herbicides. This can reduce Hoary cress to manageable levels (CSU, 08/08).

General Information on Hoary Cress:

Natural Resource Conservation Service

Website with general information about Hoary Cress including distribution and legal status

Colorado State University Extension

Website with general information and links about Hoary Cress

Colorado Weed Management Association

Website that provides information, habitat, identification, impacts, biology and control of Hoary Cress