Plants that don’t naturally occur in B.C. are considered exotics. When they start out-competing native plants and become a problem, then they are considered invasives. Invasives get here in a variety of ways like on the bottom of our hiking shoes, on our bike or vehicle tires, by drifting in the wind, or hitching a ride on our furry friends. Invasive plants are opportunist: once they find an opening, they get established, reproduce rapidly, and often out-compete native vegetation.
Invasive plants can cause environmental and economic harm, affect livestock health, destroy farming equipment, and decrease biodiversity across the landscape. For example, kudzu was introduced from Asia into the southern US as an ornamental vine. It grows up to 30 cm a day and soon overgrows anything in its way. Locally, purple loosestrife is an aggressive perennial that damages wetlands.
Invasive plants have a long history with human management practices. For years we have been working hard to keep invasives at bay by using various treatment methods. Typically three forms of management practices have been used: mechanical treatments such as mowing or hand pulling, herbicide treatments annually or periodically, and the little known method of using biological controls.
Biological control, also called biocontrol, uses parasites, predators, and pathogens to reduce the density of invasive plants to an appropriate level. The biocontrol agents may limit reproduction and diminish the ability of invasives to compete with other native plants.
Biocontrol is meant to be selective, meaning that they are targeted to a specific plant species. Biological control can be sustainable. It can provide long-term control while reducing supply and labour costs associated with repeated mechanical or chemical treatments. Biocontrol agents are often self-perpetuating. Once established, they will reproduce and continue to control the invasives, requiring little to no monitoring. In the best case scenario, when the population of invasives declines, so will the biocontrol.
Biocontrol in Canada began in 1951 with the release of a leaf-eating weevil set to control St. John’s wort. This beetle is now wide spread across Canada and has limited or reduced St. John’s wort density.
Locally another weevil has been used to limit Dalmatian toadflax. It has proven to be capable of reducing the plants’ density significantly.
Biocontrol doesn’t have the problem of harmful chemicals because it’s completely organic. However, it does comes with its own problems. Imagine intentionally introducing an exotic species to control an invasive one …have we just introduced another invasive? For example, cane toads were introduced into Australia to control a sugar cane beetle and soon became an even bigger pest.
The mongoose introduced into Hawaii to control rats devastated bird populations. Careful selection of biocontrol agents is required along with extensive experimentation in a controlled environment before release into the wild. It’s actually illegal to introduce a biocontrol without proper authorization.
As more research is done, we can learn from our successes and our failures. Fighting invasive species in our ecosystems is a constant and dynamic battle. If we cannot eradicate the population of invasives we may at least have the ability to reduce their populations to an acceptable level. As with any invasive species management, a healthy native population is necessary to help to keep the invasive species at bay.
Tiffany Muncaster and Rylan Pretty are second year recreation, fish and wildlife students at Selkirk College in Castlegar.