White Top or Hoary CressBrassicaceae or Mustard Family
Cardaria draba

IDENTIFICATION
Growth habitat: Perennial, grows up to 2 feet tall.

Leaves: Rosette leaves are blue-green. Stem leaves are blue-green to gray-green and arrow-shaped with occasional finely toothed edges. All leaves are covered with soft white hairs. Leaves of the lower stem are on stalks, while leaves of the upper stem attach directly to the stem with two clasping lobes.

Stems: Slender stalks that are about 1/2 inch long.

Flowers: Four white petals arranged in a cross. Dense clusters of small flowers create the white, flat-top appearance. Bloom in May and produces seeds a month later.
Whitetop or Hoary Cress RosetteRoots: Vertical taproots and rhizomatous lateral roots. Vertical taproots reach a depth of 12 to 30 feet by the second or third growing season. Lateral roots eventually turn down to become vertical roots, which often reach greater depths than the parent roots. Both roots produce adventitious buds, which develop into rhizomes and shoots. A single plant can produce 50 shoots per year with competition.

Seeds: Seed capsules are broad, flat, heart-shaped pods with two reddish-brown seeds. A single plant can produces from 1,200 to 4,800 seeds each year. Seeds are viable for about three years.

Reproduction: From vegetative root segments and seeds.

Habitat: Open, unshaded areas. Found in disturbed areas dominated by other exotic species.

MANAGEMENT OPTIONS:

Hand pulling:  The tremendously deep and rhizomatous root system of whitetop makes hand pulling an ineffective management tool in all situations except infestations that are very small and new.

Mowing:  While mowing may reduce seed production and biomass, it is not considered a viable management tool for whitetop.

Biological control:  N/A

Grazing:  Cattle, sheep and goats will all utilize whitetop; however, this species contains toxic levels of glucosinolates which cause anti-thyroid symptoms in livestock.  Recommended time for grazing is from the rosette to bloom stage when levels of glucosinolates are lowest.  As with mowing, grazing will reduce biomass and seed production, but will not effectively manage whitetop infestations.

Herbicide:  Whitetop can be controlled with a number of herbicides, but it is difficult and usually requires a number of reapplications.  The following herbicides are recommended for control of whitetop.  Always consult product labels and read them carefully to ensure correct species/land management usage and chemical application.

Trade Name: Active Ingredient: Rate: Efficacy: Comments
 Escort metsulfuron  1 oz/acre  most effective if applied on rosettes in spring or fall   Cannot be used near wells, surface water or shallow ground water
 Telar chlorsulfuron  1 oz/acre  most effective if applied on rosettes in spring or fall   
Roundup glyphosate per label instructions will not kill below ground roots, plant will resprout Non-selective and must be applied very carefully to prevent damage to non-target species.
 2, 4-D 2, 4-D  2 quarts/acre will not kill below ground roots, plant will resprout  
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