Vail Daily Weed of the Week: Hoary cress or whitetop |

Vail Daily Weed of the Week: Hoary cress or whitetop

Gregg Barrie
Weed of the Week
Vail, CO Colorado
Special to the Vail Daily/Chris EvansVail Daily Weed of the Week: Fuzzy grayish green leaves and flat-topped white flowers are distinctive characteristics of Whitetop, which is also called Hoary Cress.

VAIL, Colorado –This early-blooming member of the mustard family is currently beginning to bloom throughout Colorado’s Vail Vlaley and invades rangeland, pasture and roadsides and other disturbed sites. This plant is targeted by Eagle County’s municipal and county noxious weed management programs.

• Perennial growing 10-to-18-inches tall.

• Clusters of white flowers with four petals give the plant a white, flat-topped appearance, providing it with its name.

• Reproduces by seeds and extensive creeping roots.

• Roots have been found at a depth of up to 30 feet.

• Blooms from May to July, setting seed soon after.

• Heart-shaped seed capsules.

• One plant can produce up to 5,000 seeds.

• Leaves are oval shaped, clasp the stems, and blue green in color with fine white hairs.

• One of the first plants to come up in the spring.

• Hoary cress can often be confused with field pennycress. They are both members of the mustard family, and both have white flowers of similar shape. However, field pennycress comes up earlier, has darker green leaves with fewer hairs and has whorled flowers (come up the stem like a spiral staircase). They are both weeds, but field pennycress is not on the noxious weed list, and differs from hoary cress in many ways.

• Mowing two to three times a year can exhaust the root system, slow the spread of the plant, and reduce seed production but will not kill it. Mowing should be done around June, before the bud stage and repeated when plants re-bud to prevent flowering.

• Herbicide use is recommended to completely kill this tough weed since its root system is so large. Using a chemical in conjunction with mowing is one of the best ways to control hoary cress. Remember that an herbicide must be used on actively growing leaves, not freshly cut stems. Contact Eagle County Weed and Pest for herbicide recommendations.

• Another mechanical method is to completely till the plant and soil around the plant right before the flowering stage, and continue tilling every 10 days throughout the growing season. This method could take years to be effective.

• Maintaining healthy native plant communities is the best way to prevent the establishment of hoary cress. This plant quickly invades disturbed areas so proper revegetation is critical to controlling this plant as well as other noxious weed species.

For more information on these plants and the Weed Management Programs in Eagle County, visit or Or call the Eagle County Weed and Pest Department at 970-328-3540, the town of Vail Department of Public Works 970-479-2158, or the Eagle County Extension Office at 970-328-8630.

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