Working together to strengthen and support noxious weed management efforts in Montana.

Hoary Alyssum

Weed of the Week – Hoary Alyssum

Thursday, November 11th, 2010


Hoary alyssum is native to Europe and Asia.  It is often confused with another noxious weed, perennial pepperweed.  They have similar shapes and seed attachment.  These plants are both included in the mustard family and are therefore related.  Hoary Alyssum is a newly state listed noxious weed in Montana.  It was listed in 2008 and seems to be popping up everywhere.  This plant can be found throughout Minnesota, the upper midwest, and the western states.  It prefers disturbed sites but can also be found in meadows and pastures.  It is adapted to dry conditions on sandy or gravely soils.  Hoary alyssum prefers direct sunlight but will tolerate shade.

Concerns Hoary Alyssum can be an annual, winter annual, biennial, or a short-lived perennial and is spread only by seed.  It spreads rapidly because each plant produces many seeds.  It has been found to be toxic to about half of the horses that ingest it.  If a horse is going to react to it they will in 12-24 hours after ingested.  The signs include swelling of the lower part of the legs, fever of 103 or higher, warm hooves, pronounced digital pulse, stiffness of joints, reluctance to move, and very rarely death.  Horses have reacted to both fresh plants and plants that have been cut in hay.

Identification The rigid stems are hairy, 1-3 feet tall, and grayish-green in color.  These stems branch many times near the top.  The alternate leaves are oblong, also grayish-green, and covered in rough hairs.  The white flowers are clustered at the tips of the branches.  Each flower has four petals that are deeply divided.  There are seed pods located up the stems below the flowers and they are hairy, oblong, and appear to be swollen with a point on the end.

What can you do? A healthy community of native plants will definitely help prevent the establishment of hoary alyssum.  Hand pulling or digging and mowing can be effective in controlling small infestation but must be done before flowering.  There are several effective herbicides but often more than one application is necessary for control.  For best results, herbicide must be applied before flowering.  If you have infestations of hoary alyssum and they are already flowering hand pulling and mowing before seed set is the best option.  If you have questions about this plant or any other plants please contact your local county weed district.

Visit the MWCA Weed ID pages for additional information and pictures of hoary alyssum.

This series of articles was developed by Ravalli County.  If you would like to use these articles please contact Ravalli County Weed District Weed Coordinator at (406) 777-5842.

Hoary alyssum–A weed to watch for on your property

Friday, August 20th, 2010


Dr. Jane Mangold, MSU Assistant Professor and Extension Invasive Plant Specialist, just published an article about a weed to keep an eye out for during the late summer.    The following is an excerpt from her article:

Have you noticed a small, white-flowered mustard growing prolifically in your neighborhood? It could be the noxious weed hoary alyssum (Berteroa incana). Hoary alyssum was added to the state noxious weed list in 2008, and may not be as familiar as other notables like spotted knapweed, Canada thistle or leafy spurge.

However, if you live in southwestern Montana, where this weed is most prevalent, you’ve probably seen it along a bike trail or road, in a waste area or pasture, or even in your yard. It flowers from spring through late fall, and is currently very noticeable as other vegetation begins to die back for the season.

Read the complete MSU news article here.

Visit the MWCA Weed ID pages for additional information and pictures of Hoary alyssum.

Mapping the Weeds on the Madison River

Wednesday, August 4th, 2010


Bozeman Daily Chronicle recently featured an article about mapping weeds on the Madison River.

ON THE MADISON RIVER — Floating along the shoreline in his drift boat, Travis Morris pointed to a 25-yard stretch of purple flowers.

“That’s a huge infestation right there,” Morris said.

The flowers, better known as Canada thistle, look pretty. But the plant is actually a weed that takes over any ground it comes in contact with and chokes out native plants. And without those native plants, the riverbanks erode, water quality deteriorates and fish can’t reproduce.

“This river is in a spot where the weeds are here, but they can still be controlled,” said Matt Wilhelm, education director for the Livingston-based Center for Aquatic Nuisance Species.

Wilhelm and Morris, president of the Bozeman chapter of Trout Unlimited, floated the Madison on Tuesday looking for noxious weeds and recording their location with GPS coordinates.

Read the complete article on the Bozeman Chronicle website.

Biology, Ecology and Management of Hoary Alyssum (Berteroa incana L.)

Monday, April 5th, 2010


MSU newest publication is now available.

Hoary alyssum is an exotic annual to short-lived perennial forb designated as a noxious weed in Montana since 2008. Toxicity to horses has been reported when green or dried forage is contaminated by more than 30 percent. It can proliferate in forage crops, pastures, and rangelands and rapidly fills in areas disturbed or overgrazed. Maintaining healthy stands of vegetation and reseeding after major disturbances are the best ways to prevent establishment. Herbicides are an effective control option, and repeated applications may be necessary to treat plants that emerge throughout the growing season.

Download this booklet from Montana State University Extension.