Hoary Cress (whitetop)

Hoary cress is an early-season, herbaceous perennial in the Brassicaceae (mustard) family. It produces multiple erect stems that may reach up to 2 feet tall. Stems are covered in short hairs and are usually unbranched. Basal leaves have stalks or petioles; upper leaves are arranged alternately and clasp the stems. Leaves are gray-green to blue-green in color and pubescent. Leaves may be between ½ to 4 inches long and 0.1 to 1 ½ inches wide with basal leaves narrower but longer than those on the stems. Hoary cress flowers from mid-spring to mid-summer. Flowers occur in clusters at the end of stems. In the bud stage, flowers resemble small heads of broccoli. Individual flowers are small, white, and contain 4 petals. Hoary cress has an extensive, rhizomatous root system that may reach more than 10 feet deep. Seeds are produced in small, heart-shaped, or ovate seed pods and are small and reddish-brown.

Hoary cress foliage contains glucosinolates and is toxic to cattle.

Hoary cress is native to Eurasia and Central Asia. These species have multiple introduction points in North America: contaminant in alfalfa seed, ornamental use, and possible garden plant. Hoary cress spreads by seeds and creeping roots creating dense infestations. It can be transported to new locations by seeds and root fragments. Hoary cress is frequently found in disturbed sites, pastures, livestock paddocks, and landscaping. In Teton County, spread to new locations appears to occur primarily through contaminated hay, soil, and construction equipment.

Prevention and cultural control strategies should be utilized as much as possible.

The United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) approved the first release of a new biological control agent Aceria drabae, a gall-forming mite, in Wyoming in 2022. This agent has not yet been released in Teton County as infestation densities are likely to be too low for establishment. 

Hand pulling and digging out of the taproot and all lateral roots may be effective for removing small patches of young hoary cress plants, but efforts must be repeated frequently throughout the growing season and for multiple years. Tillage may also be effective if repeated at 10-day intervals and while taking great care to prevent spreading root fragments to new areas. Grazing with sheep or goats can prevent seed production and reduce rootstock. Do not graze with cattle.

Large and established infestations can be controlled with herbicides. Spring treatments during the bud or “broccoli” stage are most effective, but late treatments may also be effective at depleting the root system. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.

• Weed Report: Hoary cress (whitetop), lens-podded and hairy whitetop (2013) DiTomaso, J.M., Kyser, G.B. et al. Weed Control in Natural Areas in the Western United States. University of California Weed Research and Information Center.
• Whitetop: Lepidium draba. Idaho State Department of Agriculture.
• Hoary Cress Whitetop: Options for Control. Lincoln County Noxious Weed Control Board.
• Weed Profile: Whitetop (Hoary Cress) (2005) Colorado State Parks Best Management Practices.