Cardaria draba
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Whitetop being observed by Sari.  Photo by T. Breitenfeldt Roots: Wide spreading and penetrate deeply; thick and grow vertically and horizontally, producing side shoots from the rootstocks. (1, 3, 4)

Stems/Leaves: Grows from 1.5 feet to 3 feet and is slightly hairy. (1, 2)  Stems are medium thick and branch out toward the top of the plant. The upper leaves clasp the stem with two lobes. The leaves are blue-green or gray-green in color. (1) The leaves are serrated, or have jagged edges. The leaves alternate, or are staggered. They are irregular and lance-shaped. (1, 3)

Flowers: Small and four-petaled. They are compact with many flower branches. (1)  This produces a flat-topped appearance from which the plant received its name. They usually bloom from late April to early June. (2, 3)

Fruits/Seeds: Occur from in heart-shaped pods. Their color is a reddish-brown.  They are granular, or grainy and oval-shaped. They are released toward the middle of summer. (4)

Methods of Reproduction/Spread: It reproduces by its rootstocks, creeping  roots, and by its seeds, which float on water. Root fragments are the most efficient means of reproduction. (4)

Life Style/Habits/Life Duration: It is a perennial weed. That means that it lives for more than one year. It infests pasture areas, roadsides, and waste areas and is on the increase in the Whitehall, Montana area. (2)

Montana Infestation/History: It currently infests 56,000 acres in Montana. It is also declared a noxious weed in Washington, Oregon, and Idaho. (1)

Environments Favorable to Infestation: It favors alkaline soil (soil that is laden with mineral salts), disturbed soils (soil that has been turned and/or cultivated), overgrazed areas, and other areas where the native plants are having problems growing. (1, 5)

Impacts: It increases soil erosion and decreases desirable plants. It pushes out the native plants. (4)

Comments: It is a very aggressive plant. It is competitive with the native plants and eventually eliminates the desirable plants completely. It is a member of the mustard family. (1, 2)

Native Range/ Probable Entry into N. America: It originally came from Eurasia, its native range.  It started its infestation late in the 1900's along the East Coast, and gradually spread to cover the entire nation, except for the bottom of California east to the bottom of Mississippi. It is thought to have come over as seed in the soil used as the ballast of sailing ships. Also, some think that it came as an impurity in mattress material, carried over in 1809. (5)

Methods of control: "how-to":

Chemical: The chemical controls for it are Round-Up, glyphosate, applied as a 2% solution at its flower stage, 2,4-D applied 3 quarts per acre two to three times a year for two or three consecutive years. Non-crop herbicides, herbicides not commonly used on crops, such as Escort and Telar work well also, but they need rainfall to go into effect. (2)

Cultural: Mowing-with a lawn mower or weed whacker (4)
Cultivation-continuous harrowing of the soil during the bud stage and when it is re-budding (2)
Don't overgraze with animals because they eat down and trample the native plants, leaving the Whitetop to flourish. (4)

Biological: Sheep-eat it when it is the most abundant food source, they tend to like the buds Goats-eat it and other weeds, just for something to eat.  Cattle-eat it, but rarely and tend to eat it more in the spring (4)

How to Prevent Spread: By washing your vehicle (especially the undercarriage) after driving out of an infested area, you will wash off most of the seeds and plant fragments. Before shutting your vehicle's door, check and make sure that no seed heads are going to be shut in with you, or the next time you open your door, some might fall out and infect yet another area. (5)

Literature Cited

1. Cooley, A. Wayne. WHITETOP (HOARY CRESS) Cardaria draba HIGHLY COMPETITIVE PLANT SPECIES. [Online] Available, August 30, 1999.

2. Colorado State University Cooperative Extension. Weeds in Northwest Colorado. [Online] Available, September 1, 1999.

3. Hoary Cress (Whitetop) (Cardaria draba). 1995-2007. Larimer Country Colorado. 3/15/2007.

 4. Breitenfeldt, Todd. Personal Interview, Biology Teacher, Whitehall Schools, Box 1109, Whitehall, Mt 59759, (406)287-3862.

5. Wyoming Weed and Pest Council. Weed Handbook, Series 1-30. Box 728, Douglas, Wyoming 82633, (307) 358-2775.

By Sarah Downs
Published By Joe Wilson      Updated by: Chad Smith & Justin Gnerer 3/15/2007 HOME       Back