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  • Writer's pictureJen Haynes

Hoary Alyssum the Toxic Invader

Did you know that hoary alyssum is not only invasive it is also toxic to horses? It can cause pregnant mares to abort their babies, cause lameness and several other problems. In rare cases it can be fatal.

Hoary alyssum is an annual to short lived perennial in the Mustard family. It grows up to 0.7 m tall and mature plants have multiple stems and branching with clusters of small white flowers at the end of the branches. The flowers are white with four petals, but it looks like 8 because of the deep cleft down the middle of each petal. The whole plant is covered with hairs giving it a pale light-green colour and rough texture that feels like sandpaper. The leaves are small and alternate. The seed pods are oblong and flattened, each containing 7 to 12 seeds and are located below the flower heads. Hoary alyssum is in the mustard family so the seeds may be viable in the soil for up to nine years but most of them will germinated in the first 2 years.

Hoary alyssum (Berteroa incana) is designated as noxious under the Weed Control Act and therefore it is the duty of all landowners to control it. Mowing and weed whacking are not effective forms of control. It may slow down seed production in the short term but in the long term it makes it worse. Currently there is no biological control available. The best options are to treat it with selective herbicide or pull it by hand. No matter what form of treatment you use it is important to reseed afterwards to help create competition. When you pull hoary alyssum, you need to double bag it and take it to the landfill. There is no charge to take invasive plants to the landfill in our Regional District. In the Boundary, the Regional District has an Equipment Loan-out Program for residents to use on their private land. There are four different types of sprayers available and there is also an ATV mount seeder. The RDKB does not supply herbicides. Manuals on operation of the equipment and information on safe herbicide application are provided. In Electoral Areas D and E there is a cost share program. Requests are considered in the order that they have been received. The maximum area treated is 5 acres per parcel. Any requests received after the maximum budget has been reached will be deferred until the following year. The program does not do in-crop or pre-plant treatment. For more information on the RDKB programs, treatment options and invasive plants in general you can contact the Boundary Invasive Species Society at, Facebook, and 250-446-2232.

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