Monday, August 30, 2010

Invasive weeds in the Gulf Islands - something other than broom and gorse

Scotch Broom

We are all familiar with many of the invasive weeds of the Gulf Islands, most notably broom, gorse and thistles. Non-native invaders have come to the Gulf Islands both intentionally and accidentally. Some homesick Brits liked the yellow flowers of broom and brought them along. On the other hand, some early settlers were most dismayed to find thistle seeds smuggled in with their imported grass, vegetable and flower seeds for their newly cleared land. Transport by vehicles, road clearing and highways equipment, and even wildlife and migrating birds have spread weeds as well. They become invasive due to a lack of natural predators or diseases that help to control them.
Yellow star thistle
Hay can be one way weeds are introduced to farms. A few years ago we bought alfalfa that came from Washington. Some of the bales had a small extremely sharp sticky thistle called a star thistle. It injured some of the sheep's mouths, and would stick to clothing. It didn't take hold and spread its seeds here, but it was a close call. This particular weed originated from the Mediterranean, and prefers a hot, dry, Mediterranean climate (like the Gulf Islands) and is on the “watch” list for BC.
Rhinanthus minor "Rattle box"
One weed that appeared in our pasture was identified as Rhinanthus minor, or rattle box, a European native. It is also known as “the vampire plant” because it is hemiparasitic, attaching to the grass and sucking its nutrients. This creates a stunting and clearing effect on the grass, allowing other plants to seed the area. One source of this weed is in wildflower mixes, and rattle box is sold in the UK to aid in creating wildflower meadows. Not very helpful at all if your goal is to grow grass. We tilled and re-seeded, ending up with the sprouting of some dormant thistles. And so it goes.
Tansy ragwort "stinking Willie"
Common tansy
In the past few years, some new weeds have appeared and have the potential to create problems for farms in the Gulf Islands. One of those stowaways that came in with the European settlers is Tansy Ragwort. It is already a problem in the Fraser Valley, and this year I noticed a few of the bright yellow flowers along the roadside on both Pender Islands. The leaves of this weed are “raggedy”, the stems long, and the flowers are a bright yellow, arranged in a dense cluster of flowers with a button centre and 10-15 petal rays like small daisies. They can be spread by animals, brought in with hay, or more commonly by the wind. They look a lot like common tansy which has a button flower without the rays, and is also seen here and there along the road. Each plant can produce 150,000 seeds per year and the seeds can survive 15+ years in the soil, so it is important to pull the plants, including the roots, before they go to seed. This is especially important to farms, because the plant can take over pastures and is poisonous to deer, cattle, pigs, horses and goats. The alkaloids in the plant cause cumulative liver damage, and produce a bitter flavour in honey. There are some reports of sheep tolerating it, but given its ability to spread and take over it is best to control it. In Europe, sixty insects control the plant. In Oregon three insects have been imported to control the weed, and the Cinnabar moth and tansy flea beetle have worked the best. The Cinnabar moth has also been useful in controlling the weed in BC, and in the Nanaimo area there is a valley named for it - the Cinnabar Valley. In the Fraser Valley in heavily affected areas, bio controls using defoliating and root-crown feeding moths, seed head flies, and root-eating beetles have been helpful as well.
In the battle to control weeds on farms, we are helped by the Invasive Plant Council of BC and its regional committees. The IPCBC started after members of the Fraser Basin Council had a field trip to the Cariboo in 2001 and saw the devastation of invasive weeds. They developed an Invasive Plant Strategy for BC, which was intended to address the explosion in invasive plants in BC. The IPCBC is a registered, non-profit charity whose members are involved in all aspects of invasive plant management and agree to work cooperatively. Members include technical specialists working for government and industry, weed committees, First Nations, foresters, forest technologists, biologists, ranchers, farmers and farm groups, horticulturists, recreation enthusiasts, gardeners, and other concerned individuals. Membership is open to everyone willing to work collaboratively. The Gulf Islands are included in the region covered by the Coastal Invasive Plant Committee. 

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