RED DEER – Controlling weeds through biological control is like running a marathon – it’s not fast, but eventually you have success.
Brian Van Hezewijk, a researcher specializing in biological control with Agriculture Canada in Lethbridge, said finding and releasing insects that control invasive weeds is a long-term but effective method of weed control.
“It has the potential to be a very powerful tool we can use,” Van Hezewijk said during an Alberta Invasive Plants Council meeting in Red Deer.
Researchers have released insects on 548 sites in Alberta since 1999 to control a variety of invasive plants including leafy spurge, knapweed, dalmatian toadflax and hound’s-tongue.
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Van Hezewijk said researchers know the insects help control weeds, but they don’t have a good handle on the acres of invasive weeds across the province. Most municipalities know where some of their problem weeds are, but that information isn’t tracked by any one group.
“We can’t solve the problem if we don’t know where the weeds are. We know it’s having an impact but we need convincing data,” he said.
A study of leafy spurge in Montana, South Dakota, North Dakota and Wyoming estimated damage at $40.2 million in direct costs and $90 million in indirect costs.
The projected annual cost of leafy spurge to Canadian agriculture is $4.5 billion a year if it’s not brought under control.
“$4.5 billion from one single weed in Canada seems pretty significant to me,” Van Hezewijk said.
“The case is very good that species like leafy spurge are having a big impact on the economy.”
Biological control uses live organisms to suppress an introduced pest with minimal impact on the native population.
Other control methods include chemicals, especially in the early stages when the weed patches are small, and cultural methods, such as changing grazing patterns.
A combination of all methods is ideal, he said.
Van Hezewijk said the first question landowners ask when approached about releasing insects on their land is: “Will it attack my canola?”
Horror stories of early biological control methods gone wrong are long lived.
The early theory was a predator would die once it had eaten all the problem weeds or pests. In reality, many adapted to a new food source. In the past 10 to 15 years, there have been no negative effects from releases because of scrutiny before the pest is released.
The first step in biological control is assessing the native species and how the weed or pest is affecting it. Van Hezewijk then searches for insects around the world that may be useful in a biological control program.
Plants have different vulnerable stages, so it’s important to find insects most suitable for control during those stages.
Leafy spurge seeds are released by the millions, but most die because of overcrowding.
Instead of focusing on finding an insect that attacks the seed, researchers have focused their energy on finding an insect that feeds on the adult plant.
Researchers must also assess the area where the insect is to be released to ensure it won’t feed on other plants.
Experts and local agencies review a proposal once it is approved and a small number of insects are then released into the field.
If the final impact is deemed a success, the insects are redistributed to other sites.
It typically takes 10 years to go from talking about the problem to redistribution.
Van Hezewijk said a release of a knapweed seed-head fly in White Lake, B.C., almost eliminated knapweed in five years.
A hound’s-tongue root weevil dramatically reduced weed patches in range land in Alberta and a toad flax stem-weevil has done a good job of reducing patches of dalmation toadflax in British Columbia and southern Alberta.
St. John’s wort had taken over two million acres of range land in California in the 1940s. Within 10 years of releasing Klamath weed beetles for its control, the weed was almost eliminated. Local landowners erected a plaque commemorating the insect.
Insects have also been released to control leafy spurge with varying success.
Two leafy spurge flea beetles seem to have a significant impact in some areas, Van Hezewijk said.
“They cleaned up fields quite nicely and got good regrowth on grass.”
