Hoary cress, greyish-green leaves, lance-shaped with clusters of four-petal white flowers.Hoary cress (Whitetop), a member of the Mustard family, was probably introduced from Europe in alfalfa seed. It is a creeping perennial, which reproduces by seed and creeping roots. The extensive root system spreads horizontally and vertically with frequent shoots arising from the rootstock. It grows erect from ten to eighteen inches high and has a gray-white color.

The alternate leaves clasp the stem and are oval or oblong with toothed oral most smooth margins. The leaves are often covered with very fine white hairs. Each leaf is 1/2 to two inches long with blunt ends. The flowers are white, 1/8 inch across, and numerous in compact flattop clusters, which give the plant its name. Each heart-shaped seedpod contains oval, finely pitted, red-brown seeds each about 1/12 inch long.

Hoary cress is one of the earliest perennial weeds to emerge in the spring. Flowers are produced in late April and May. It grows in waste places, cultivated fields, and pastures, and is capable of vigorous growth on the irrigated, alkaline soils of the West. It is a major problem in certain pastures and cultivated areas in Colorado from 3,500 to 8,500 feet.

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.

Hoary cress, greyish-green leaves, lance-shaped with clusters of four-petal white flowers.  Hoary cress, greyish-green leaves, lance-shaped with clusters of white flowers.


Hoary cress infestation along a disturbed area.
Description:
  • Whitetop, a member of the mustard family, is a creep-ing perennial with numerous small, white flowers that appear in May to early June 
  • Flowers have 4 petals on stalks radiating from a stem
  • Leaves are 3/4 to 4 inches long with a blunt end and fine white hairs
  • Mature plants grow 10-24 inches tall
  • Reproduces by seed and creeping roots
  • One plant can produce from 1,200 to 4,800 seeds
  • Generally grows in sunny areas with moderate amounts of precipitation and does well on alkaline soils
  • Occasionally found growing with Russian knapweed infestations

Negative Impacts
  • A problem in fields, pastures, croplands, meadows, waste places, along roadsides and natural areas
  • Reduces agricultural production
  • Grazing animals and wildlife do not eat Whitetop
  • Infestations reduce or eliminate wildlife use


Chemical Control (Always add non-ionic surfactant @ 1 oz for each 3 gallons of water)

Read Labels for safety info & to see if products are approved for your site or near desirable trees.
Treatment Timing: Apply at early bud (pre-bloom) up to early flowering growth stage (Mid to late spring)
After seeds have formed is the worst time to apply herbicides.
  • 2, 4-D Amine (Phenoxy)
    • 1 to 2 quarts per acre
    • Spot treatment: 2 to 3 oz per gal of water
  • Escort XP (Metsulfuron)
    • 1-2 oz per acre
    • Spot treatment: 1 gram per gal of water (there are 28.3 grams in one ounce)
  • Telar XP (Chlorsulfuron)
    • 0.5 to 1 oz per acre to active growing plants from rosette to bolting
    • Spot treatment: 1 gram per gallon of water (there are 28.3 grams in one ounce)
  • Perspective (Aminocyclopyrachlor)
    • 3 to 4.5 oz per acre
    • Spot treatment: 0.6 to 0.9 oz per 5 gallons of water based on 1 gal covers 1750 sq. feet

Mechanical Control:
  • Mowing several times at bud (pre-bloom) growth stage followed with a fall applied herbicide will improve control
  • Stopping flowering and seed production is critical for success

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