Wireworms prove tricky to keep under control

New product is welcome because populations have been building in some parts of the Prairies due to lack of solutions

Wireworms are not easy to study.

A particular field probably has more than one species of wireworm, they live for several years and they can tunnel a metre down into the soil, making them hard to find.

That means it’s difficult for scientists to answer some basic questions about wireworms. Like, how many wireworms will cause crop damage?

“If you have a trap and there are two wireworms in it, is that a problem or is it not a problem? We don’t know,” said Haley Catton, a cereal crop entomologist with Agriculture Canada in Lethbridge.

Wireworms are a problem for many cereal growers in southern Alberta and parts of southern Saskatchewan. Wireworms, the larval stage of click beetles, like to feed on cereal crops during the early stages of the growing season and cause thinning of the crop or yellowing of the plant.

“They come up close to the soil surface and they’re detecting anything that produces CO2. (That’s) what germinating seeds produce,” Catton said. “A very young, young plant, or even a seed that’s just germinating, is very vulnerable to death with just a few bite marks in the right place.”

Growers have been struggling to find a solution to wireworms, but a new insecticide from BASF may become a large part of the solution.

BASF has developed Teraxxa, a new active ingredient to control wireworms. In June, Health Canada issued a proposed registration for the active ingredient broflanilide, “to be used as a soil treatment to control wireworm in potatoes and wireworm and corn rootworm in corn, and as a seed treatment to control wireworm in small cereal grains and wheat.”

BASF is waiting on a final decision from the Pest Management Regulatory Agency.

“We’re anticipating registration here shortly, but we are still awaiting that update,” said Chris Hewitt, BASF marketing lead for seed treatments and agricultural solutions in Canada.

“Once we get that update, we’ll be looking at full launch for Western Canada for the 2021 season.”

A new insecticide seed treatment to control wireworms is needed because existing products don’t kill the wireworms. Neonicotinoid seed treatments suppress activity and discourage feeding, but don’t kill the pests.

Rotating crops away from cereals isn’t particularly effective because the wireworms persist in the soil, will feed on pulses and probably feed on canola.

“Unlike some other insects, it’s really hard to subdue them with rotation,” Catton said.

“There’s a little bit of evidence that certain crops, like brown mustard that’s plowed in, could fumigate them out of the soil.”

Many farmers in the light brown soil zones, in southern Alberta and southwestern Saskatchewan, are probably desperate for something that kills wireworms because populations have been building up in the soil.

“We know that growers aren’t satisfied… with the level of control they’re getting,” said Alison Friesen, a BASF technical marketing manager in Canada. “From the species we’ve tested, it has pretty broad-spectrum control on all different types of wireworms.”

A product that kills wireworms and reduces populations would be a game changer for control, Catton said in an email.

But insecticides should only be used when needed.

Some cereal growers in Western Canada will need an insecticidal seed treatment for wireworms. Others may not.

“It’s all the people that are not sure…. At what level of wireworms do you need these (products)?” she said.

Scientists have devised an economic threshold for many pests, which tells growers when to use an insecticide.

With wireworms, there is no economic threshold.

“Each one has their own behaviours… they have their own feeding behaviours,” Catton said, noting economic thresholds are usually created for a single species.

“What happens when two species are in the same field, which happens a lot?”

Catton and her pest management colleagues are studying better ways to monitor wireworm populations and hope to make advancements on an economic threshold in future projects.

Agriculture Canada plans to soon release a field guide for wireworms on the Prairies, so growers have the latest information on wireworms, Catton said.

“A state of where we are with this pest.”

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