Extension Viewpoints: Noxious weed of the month: hoary cress

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Photo courtesy Jamie Jones
Hoary cress.

By Ethan Proud
PREVIEW Columnist

As the snow melts and we begin to see the first sprouts of spring, it’s important to keep your eyes peeled for early season invaders such as hoary cress. 

Hoary cress, or white top, is a perennial species that spreads both by seeds and creeping rhizomes (lateral roots). That means that an infestation of hoary cress is a single clonal colony rather than individual plants. Hand-pulling or mowing this species will increase propagation.

While hoary cress is in the mustard family, along with broccoli, kale, cabbage and others. It contains toxic glycosides despite being palatable. It is toxic to both livestock and humans and should not become a staple of your wild plant salad bowl. 

Currently, chemical controls are most effective on this species, though it can be controlled mechanically with a lot of persistence. Hoary cress can be recognized by its clasping, hastate leaves. In lay terms, the leaves join the stem and are shaped like an arrowhead. 

There are several different biotypes in Archuleta County and it may be mistaken for penny cress, a native species in the same family that can be quite aggressive. If you pull the plant and the entire root comes out, it is penny cress.

Hoary cress is tricky to control as it emerges early and goes dormant by mid-June or early July. It can be treated up until flowering, or in late fall when its rosettes sprout to sequester nutrients in order to overwinter.

Archuleta County Weed and Pest is your local resource for managing noxious weed populations and controlling other pests.