City tests weevil weed whacking effectiveness
Camrose Parks Director Chris Clarkson says the City has released stem-mining weevils in two locations to help control the spread of the noxious weed Canadian Thistle in Camrose. Josh Aldrich/ Camrose Canadian
The City of Camrose is playing the long game in their fight to control Canada Thistle.
This summer they announced they were going to be starting a program of using stem-mining weevils to eat the noxious weed one plant at a time, and late in October they deployed them in two areas in the city.
The key was to set them out before the snow fell, so they had time to burrow into the plants, and come spring they will lay their eggs in the leaves of young rosette and go to work.
“Once they are in an area they will start moving to other locations,” said City of Camrose parks director Chris Clarkson. “They say over a 10 year period they can go nine kilometres … and if they can do that it would be awesome for our program.”
The goal is to eventually eradicate the Canada Thistle which can have a devastating effect on the local agriculture industry. According to the West-Central Forage Association, a density of 20 Canada Thistle shoots per square metre can cause estimated yield losses of 34 per cent in barley, 26 per cent in canola, 36 per cent in winter wheat, and 48 per cent in alfalfa seed. Field infestations can reach 173 shoots per square metre. The weeds are difficult to control because they spread by seed and their ability to regrow from its extensive, deep creeping root system.
Municipalities are required by law to control the weed. To do so, the City has used chemicals and sent crews in with weed whackers to knock the prickly purple weeds down before they hit maturity. The process is expensive, time consuming and carries with it its own challenges, like the inability to use chemicals near waterways.
The stem-mining weevil, however, is a biological pest control that does not have any major side effects. Clarkson said the insect will only feed on Canada Thistle, so other plants and crops are safe.
“The weevil will travel through the water system wherever there is thistle and if they don’t find thistle, they prefer to die before they take on anything else,” he said.
“They are very selective to Canada thistle.”
This weevil is native to France, Switzerland, Germany, Britain and southern Scandinavia, bit was introduced to Canada as a biological control agent in 1965. It is picking up in popularity again as several communities are starting test projects with the insect.
The weevils are also a cost-effective system as they can potentially save a lot of time and labour costs in traditional control methods. It cost the City about $300 to enter the program. They were set out in two locations — one in the north, one in the south —along Stony Creek, the most difficult areas to get in with a crew of workers and controlled areas for use of insecticide.
“It’s time consuming and it takes a lot of effort,” said Clarkson. “If we can get it before it goes to seed, it will help us out.”
However, Clarkson is preaching patience. The weevils are tiny and will take time to catch up with the weed problem. It may take a couple of years for them to make a noticeable dent in the thistle situation. In the meantime, City crews will continue to do their best to stay on top of the situation.
“It should take a while,” he said. “It’s not like when you spray them and they keel over. It’s a long-term process. You’ll start seeing effects next fall. It has proven effective in other communities that have used them.”