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KOOTENAY WEED INVASION! Help Stop the Spread of Eurasian Watermilfoil and Hoary Alyssum


by Barb Houston

Eurasian watermilfoil (Myriophyllum spicatum L.) has been a troublesome aquatic invader in British Columbia since the 1970’s, impacting waterways in the Okanagan and elsewhere. Unfortunately, a recent survey funded by the Fish and Wildlife Compensation Program and Fortis BC, confirmed that this aquatic invader has made its way into the Kootenay River system. Thick mats were detected in the Kootenay River and plants were also found at several locations in Kootenay Lake.

The problem is that this non-native, immersed rooted perennial aquatic plant spreads rapidly and forms dense canopies of vegetation. These thick beds of tangled stems can interfere with recreational activities such as boating swimming, fishing, and diving, and can also alter the ecology of a water body by reducing water quality, impacting fish and wildlife habitat and killing native plants. It is found in a variety of habitats including lakes, ponds, reservoirs, rivers and streams and can tolerate a wide range of environmental conditions. It is especially well adapted at colonizing new areas and even small fragments, such as those trapped on engine propellers or recreational vehicles, can start a new infestation, and once it is established it is nearly impossible to eradicate.

In an effort to educate the public and prevent the spread of Eurasian watermilfoil, the Central Kootenay Invasive Plant Committee, along with project partners including the Fish and Wildlife Compensation Program, BC Ministry of Environment, and Fortis BC have developed informational signs that were installed earlier this summer at several boat launches throughout the area. The goal of the signage is to inform the public about the problem, provide details on how to identify the plant and to prevent the spread by encouraging people to clean all recreational equipment including boats, trailers, motors, anchors, live wells, bilges, bait buckets, fishing and diving gear.

It can be somewhat difficult to tell the difference between the native milfoil species and the Eurasian invader, but a good rule of thumb is that generally Eurasian watermilfoil has between 12-24 pairs of thread-like leaflets; where as the native milfoils have less than 12 pairs of leaflets.

Early detection of this invasive plant is critical, so if you think you may have seen Eurasian watermilfoil, or would like more information, please contact the Central Kootenay Invasive Plant Committee by phone at (250) 352-1160 or e-mail at coordinator (at) . You can also visit their website




Horse Owners Beware of Toxic Weeds

Hoary alyssum (Berteroa incana) is an invasive weed species that has been introduced from Eurasia in “Wildflower” seed mixes and is quickly spreading throughout the West Kootenay, particularly in the Fruitvale, Harrop-Procter, and Lower Arrow Lake areas. This plant is commonly found growing in closely grazed pastures, drought-stressed meadows (particularly alfalfa fields), abandoned fields, and along roadside edges. Hoary alyssum is well adapted to dry conditions, particularly in areas with sandy to gravelly soils. Due to the recent extreme temperatures and lack of rain this summer, this plant is flourishing.
Hoary alyssum is toxic to horses, both when fresh and dried in hay, and can remain toxic for up to 9 months. Though it is not preferred horse forage, horses will nibble on it when other plants are not growing due to overgrazing and/or drought. When buying hay, be sure to thoroughly examine all bales for presence of Hoary alyssum and other Invasive plant seeds. It is often very difficult to see this plant once dried, and as little as 30% of Hoary alyssum in one bale of hay may cause signs of toxicity in horses.
Toxicity symptoms in horses range from depression to “stocking up” (swelling in the lower legs), which generally occurs 12 to 24 hours following ingestion of hoary alyssum in hay or on pasture. A fever, short term diarrhea and abortions in pregnant mares, have also been observed. These clinical signs normally subside 2 to 4 days following removal of the Hoary alyssum source. In more severe cases, an apparent founder with a stiffness of joints and reluctance of the animal to move has been observed. Recovery of animals with clinical evidence of founder may take several additional days. Some horses are extremely susceptible to the toxin, and consumption of Hoary alyssum may prove fatal.
Key identifying traits
* Flowers are white with 4 petals, deeply divided
* Usually only branched at the top of the plant
* Leaves are alternate, blades are simple, gray green in colour and coarsely textured to the touch
* Fruit is oblong, with two compartments containing 2 to 6 seeds
* Seeds grow close to stem, are round to oblong, narrowly winged, grayish-brown and rough
Minimizing problems with Hoary alyssum begins with good pasture management and controlled grazing. When this weed is found in an established pasture, hand-pulling/cutting followed by bagging and/or herbicide use are good containment strategies which should be completed before seeds ripen and spread. These plant seeds do not carry on the wind, so an awareness of it and early control can go a long way in reducing its spread. Seeds disperse primarily in contaminated hay and are often spread by vehicles, equipment, and footwear. Ensure that vehicles, equipment, footwear and clothing are free of seeds when leaving an area where Hoary alyssum is established. Taking steps to decrease transfer and ensuring that your hay and pastures are not contaminated with Hoary alyssum will go a long way in meeting the Central Kootenay Invasive Plant Committee’s (CKIPC) priority of containing the spread of this toxic invasive plant. Please contact us for more information about invasive plants at :, or call us with your questions: 250-352-1160 or call the Invasive Plant Council of BC (IPCBC) at 1-888-weedsbc