Download ALIEN PLANT INVADERS: Tansy Ragwort and Common Tansy

ALIEN PLANT INVADERS: Tansy Ragwort and Common Tansy
From a series of articles on how to identify and manage some common invasive species on Salt Spring Island
written by Jean Wilkinson, Stewardship Committee, Salt Spring Island Conservancy.
Introduced from Eurasia, Tansy Ragwort and Common Tansy are spreading rapidly throughout the Gulf
Islands, degrading pastures and disrupting native plant communities. We have the opportunity -and the
responsibility- to stop their spread by taking action now.
The B.C. Weed Control Act “imposes a duty on all land occupiers to control designated noxious
plants….to protect our natural resources and industry from the negative impacts of foreign weeds.” Like
Canada Thistle, Giant Hogweed, Gorse and Knotweeds, Tansy Ragwort is classified as a noxious weed
throughout all regions of BC. Common Tansy, a similar-looking invasive plant, is a designated noxious weed in
many Interior regions and a growing concern in the Coastal region.
So if you see a tall plant with yellow blossoms in July to September, please stop and take a closer look.
If it’s either of these weeds, pull it up or cut the flowers off into a bag to prevent seeds from spreading, and
carefully dispose of it (more info below). Working together, we can help our farmers and prevent these weeds
from spreading along roadsides and into pastures.
TANSY RAGWORT & COMMON TANSY –Facts About These Horticultural Bullies
Identification – Senecio jacobaea– biennial or short-lived perennial growing 0.3 to 1.2 metres (1-4 feet) tall, with one to
several branching stems. Tansy Ragwort leaves are dark green, without stalks, and are deeply cut and raggedlooking; its small yellow ray flowers are clustered at the tops of the stems.
Tanacetum vulgare –an aromatic perennial growing to 1.8 metres (6 feet) tall, Common Tansy has deeply
divided, coarse, fern-like leaves and yellow button flowers clustered at the tops of the stems.
Impacts – Tansy ragwort reduces forage production of pastures, and contains alkaloids that can poison livestock,
especially cattle, horses and goats. Animals should not be grazed on pastures with more than 5% cover of tansy
ragwort, and can also be affected through contaminated hay or silage. Trace amounts of the alkaloids found in
milk and honey produced from infested pastures raise concerns for human consumption. Common tansy can
also be toxic to livestock if eaten in large quantities.
Found –in grasslands, pastures and rangelands, clear-cuts, on stream-sides, roadsides and other open, disturbed areas.
Spreads –Each Tansy Ragwort plant can produce more than 150,000 seeds! Seeds of both species are transported by
wind, water and animals, or in soils on equipment and vehicles. They can remain viable for 4-5 years on the soil
surface and for over 20 years if buried. Common Tansy also spreads vegetatively via its root system.
Prevent - Infestations develop easily when soil is disturbed, so avoid this as much as possible. Maintain healthy forage or
plant cover. Overgrazing is the leading cause of pasture deterioration and rapid invasion of invasive plants.
Control – At a minimum, prevent seed formation, and note that plants cut or mown while flowering can still set seeds.
Hand pull isolated plants and small patches, removing as much of the root as possible (easiest when ground
is moist and plants not mown). Mowing or leaving root fragments in the soil promotes vegetative spread. In
heavy infestations mow often and thoroughly. Biological control insects are available for tansy ragwort.
Disposal - If plants are pulled or cut prior to flowering, they can be left on site to decompose. Otherwise all plant parts,
especially the flower heads, should be bagged and incinerated, buried deeply or taken to the landfill.
More Info: Salt Spring Island Conservancy Stewardship Committee 250-537-4877, Coastal Invasive Species Committee
www.coastalinvasivespecies.com, Invasive Species Council of B.C. www.bcinvasives.ca