Weed of the Month: Hoary Cress

Hoary Cress, also known as whitetop, is a creeping perennial from Europe that spreads rapidly through both seeds and persistent roots. Identified by its lance-shaped leaves and dense clusters of small white flowers, this invasive plant thrives in various habitats including fields, meadows, and roadsides. Its aggressive growth outcompetes native vegetation, posing significant challenges for effective management, which typically involves a combination of prevention, mechanical, and herbicide-based strategies.

Origins:

Hoary cress (Lepidium draba), commonly known as whitetop, is a creeping perennial belonging to the mustard family and is native to Europe.

Plant Identification:

In its rosette stage, Hoary cress stems may reach up to 2 inches in height, bearing lance-shaped grayish-green leaves. These leaves are alternate, measuring between 3/4 to 4 inches long, with upper leaves featuring two lobes clasping the stem. The plant produces numerous small, white flowers with four petals on stalks radiating from a stem, giving it a dense, flat-topped appearance. Stems are stout and branch towards the top.

Reproduction:

Hoary cress reproduces via both seed and vegetative means. Its seed capsules are heart-shaped, containing two small, flat, egg-shaped reddish-brown seeds. A single plant can produce anywhere from 1,200 to 4,800 seeds. Emerging in early spring, stems grow from the center of each rosette in late April. Flowering occurs from May to June, with seed setting by mid-summer.

Habitat:

Hoary cress thrives in various habitats, including fields, waste places, meadows, pastures, croplands, and along roadsides. It prefers unshaded, open areas of disturbed ground, particularly those with moderate precipitation and alkaline soils. It also adapts well to moist areas like native grass hay meadows, irrigated pastures, and riparian zones. Hoary cress often invades roadsides and areas with run-on moisture, such as drainages and irrigation ditches, posing a threat to adjacent high-value habitats.

Growth:

Characterized by extensive horizontal and vertical roots, Hoary cress frequently produces shoots from root stocks. This perennial herb can grow up to 24 inches tall and features leaves predominantly in the basal half.

Impact:

Hoary cress spreads primarily through persistent roots, ultimately outcompeting desirable vegetation and forming monocultures. Its dense populations reduce the production of desired forage species and crops, posing challenges for effective control.

Management:

Prevention:

Prevention is the most effective strategy. Minimize disturbance to prevent seed dispersal, eliminate seed production, and maintain healthy native plant communities.

Mechanical Management:

Combining mowing with herbicides enhances control. Mow repeatedly during the summer and follow with herbicide application in the fall.

Herbicide Management:

Effective herbicides, particularly those with good penetrating qualities, are essential due to the plant's soft, hairy leaves. Apply herbicides when the plant is still in the rosette stage, both early in spring and later in fall. Spraying rosettes twice a season should eradicate the weed within three years.

As always, the staff at TCWP is available to answer your questions regarding invasive plant control methods and any other inquiries you may have.

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