Hoary Cress

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Description:

Hoary Cress - Cardaria draba (L.) Desv.

Brassicaceae - (Mustard family)

A deep rooted perennial up to 2 feet tall, reproducing from root segments and seeds. Leaves are blue-green in color, lance-shaped. Lower leaves are stalked; upper leaves have two lobes clasping the stem. Plants have many white flowers with four petals, giving the plant a white, flat-topped appearance. Heart-shaped seed capsules contain two reddish-brown seeds separated by a narrow partition. Plants emerge in very early spring and have bloomed and set seed by mid-summer.

This perennial is common on alkaline, disturbed soils and is highly competitive with other species once it becomes established. It can be controlled effectively with herbicides. Two other Cardaria species, lens-podded whitetop (C. chalepensis L.) and hairy whitetop (C. pubescens (C.A. Meg) Jarmolenko) are common in the western U.S. with differences in seed capsules and fruit used to identify each species.

Non-standard name: whitetop.

(Courtesy of Weeds of the West)

Control Strategies:

Hoary Cress is very hard to control using cultural practices. The stored energy in the roots will insure that it can still produce competitive stands after three years of clean cultivation. 2,4-D is moderately effective if used twice a year. The first treatment needs to occur prior to blooming when the plants are only a few inches tall. Most of the time we are too late to get the best results with 2,4-D. Then, unless the field is being irrigated, there will be little opportunity for a fall treatment as the plant typically sets seed in May and then goes dormant. There are two much more effective herbicides, Telar and Escort. They can be applied at any time the plant is green, so that extends the window of opportunity. Small amounts of these herbicides provide 95% or better control from a single application. Escort and Telar can be applied at the rate of 0.75 to 1.0 ounces per acre. The lower rate is safer on grasses growing under droughty conditions. Escort is very hot on most shrubs and trees, so there can be considerable collateral damage from drift. Telar has more soil activity than Escort but is safer around trees and shrubs. They cost about the same and the District cost shares on the products. Use Telar where the longer soil residual will not interfere with crop rotations. Use a non-ionic agricultural surfactant at 0.5% to aid penetration of the herbicide. These herbicides react with water over time, so you should use up all your mix the same day. Caution: Telar and Escort are very hard on Kentucky bluegrass and Garrison's Creeping Meadow Foxtail. If treating Hoary Cress where these species are present you should expect to see a lot of damage. The grasses will recover, but there will be little production the year of treatment.

 To learn about biological control agents for Hoary Cress visit this link.