Idaho Weed Awareness Campaign
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Hoary Cress (Whitetop)

The Strategy: This noxious weed occurs sporadically throughout the valley. It is an escaped perennial ornamental that was originally brought in as a ground cover. The plant grows less than 18 inches in height. Multiple branches grow off of the root system and each has white flowers at its terminal end which appears as a carpet of white. It has an integrated root system that allows it to creep into unwanted places and spreads if roots are carried in the soil. Leaves are light green with a distinctive white midvein.

The Attack: This perennial plant is the first noxious weed that we attack in the spring. Right now it is starting to bolt and in about three weeks you will be able to see the formation of the white buds. The plant has rhizomatous roots (spreading) that allow the plant to spread into lawns, established plantings, and even push up roadways. Since it occurs early and develops very thick canopies, it does a great job of choking out desirable plants and the diverse root system allows the plant to absorb most of the water and nutrients.

The Defense: Mechanical control is not very effective. Many people that dig, disk, or plow this plant notice it comes back with a vengeance in a few weeks. No biological control insects are available for this plant. There is one class of herbicides that work well: one ounce of Telar or Escort during the budding stage will grant the landowner 98 percent weed control. Opensight is another product that works well. These products are very safe to use in a pastures and one does not have to remove the livestock during application. 2,4-D and Roundup will only set the plant back a few weeks.


DOW LogoOpensight at 3.3 oz product/A apply at early in the spring to actively growing rosettes or to regrowth before the bud stage or in the fall before frost. Click to view label.

Click here for information about Opensight.

Roundup plus 2,4-D is somewhat effective in ornamentals.

Mechanical control is not recommended as this plant is a rhizomatous perennial and cultivation will encourage more growth.

There is no biocontrol for the plant, but research is under way to find one.


PLEASE NOTE -The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.

For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.

U of I Idaho's Noxious Weeds Control Guidelines (183 KB PDF download)

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