B.C.’s Weed Control Act was enacted “to protect our natural resources and industry from the negative impacts of foreign weeds,” and it imposes “a duty on all land occupiers to control designated noxious plants.”
The act focuses largely on farming activities, and many listed species are problems in rangelands of the Interior, knapweeds for example, while aggressive and invasive pests of gardens and natural areas in the Lower Mainland are identified only as “common nuisance weeds.” They do not fall under this province-wide legislation.
Introduced plant species are often troublesome because they have no local pests or diseases to keep them in check, and they grow vigorously, out-competing native vegetation so that the environment is compromised and habitat altered.
This results in diminished and impoverished biodiversity.
Some have been brought in deliberately to add variety to gardens while others have been introduced accidentally.
Once established here, their seeds are spread around by winds or are eaten and then excreted by birds and small animals. So they proliferate.
Surrey Bylaw 17160 relies on provincial designations of noxious weeds and permits treatment of them with approved herbicides. White Rock has just begun to develop a policy.
Here on the Semiahmoo Peninsula, there are several invasive species that demand attention.
Scotch broom was brought in during the 1880s, possibly for sentimental reasons and for its brightly attractive yellow flowers. Also, it has been used to stabilize cut-banks and other disturbed sites because of its prolific root system.
It produces large numbers of seeds annually, suppresses native vegetations and has an acidifying effect on soil. It is difficult to control even with extensive excavation of the roots.
Himalayan blackberry is extremely aggressive and, left unmanaged, will form impenetrable thickets discouraging other plants.
It, too, is difficult to control. Successive mowings, especially when flowering, will set it back.
Since it is shade-intolerant, cutting should be followed immediately by planting quick-growing native shrubs or trees.
Excavation of each central root mass followed by seeding or planting is usually successful. However, blackberry bushes provide safe habitat for small birds and animals and produce good crops of edible berries for wildlife and humans, so controlled management is preferable to eradication.
Japanese knotweed is another plant introduced as an ornamental that can become a serious pest, difficult to control and hard to eradicate; even small portions of roots can quickly develop into healthy plants.
Its tough roots can grow through old concrete or asphalt, and the bamboo-like stems decompose slowly, building up a layer of leaves and stems, which inhibits other plant growth.
Since control is far from easy, it’s better not to introduce such invasive species at all.
Small seedlings can be up-rooted by hand, established plants call for thorough digging and excavation.
In both cases, plant material should be completely dried, preferably burned, before being disposed of.
Dr. Roy Strang writes monthly on the environment for the Peace Arch News. rmstrang@shaw.ca