Idaho Weed Awareness Campaign
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Hoary Alyssum

Hoart AllysumThe Enemy - This annual mustard plant showed up in North American in the early 1900ís. This state-listed noxious weed sends up many shoots and has clusters of white flowers at the end of each stem. These white flowers have 4 petals, like all mustards, but the petals are deeply notched to give the flower the appearance of having 8 petals. The leaves are alternate on the stem and are elliptical in shape covered with small hairs. The plant grows to a height of 2 feet. It spreads onto disturbed sites such as roadways, gravel pits, over-grazed pastures, and agriculture sites.

The Strategy - This is one mustard that is actually toxic to horses, causing leg swelling and fever. Like all mustards this plant is a prolific seed producer and spreads quickly. Germinating early in the spring gives it the ability to capture most of the moisture and nutrients from the soil. It has been seen in areas from Salmon to Driggs, and everywhere in between. It is believed that it is spread by animals as it generally is not broken off at the ground nor tumbles across the prairie like many other mustards.

The Defense - As this plant does not dwell well with competition from other plant proper stewarding of land is key to keeping this plant from invading. If you are disturbing the soil make sure that you have the ability to revegetate the land with desirable species. Donít over-graze the property as this promotes weed invasion. Once the weed becomes present mechanical removal with a shovel is effective. Products of choice would be Telar XP, Escort XP, or Opensight in the spring. There are no grazing restrictions with these products so that moving the livestock from the site is not necessary.

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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