Canola School: Watch for wireworm, the underground feeder

Wireworms are a widespread concern across the prairies early in the growing season. Kara Oosterhuis recently caught up with John Gavloski, provincial entomologist with Manitoba Agriculture and Resource Development, in this Canola School episode to talk about the insect pest that can impact your canola crop.

Wireworms are the larval stage of the click beetle and have multi-year life cycles. This means they can exist in the larval stage for two or three years, particularly for the species that dominates Manitoba. Other species found further west may last in the larval stage in the soil for as long as four or five years.

Foliar insecticides do not control them, only seed treatments do, as wireworms will never come above the soil surface to feed on leaves. As Gavloski explains, “You won’t get the insecticide down to where the wireworms are, no matter what you put on.”

There’s no research currently out there about economic thresholds, but if you want to assess levels in your fields, Gavloski suggests using a bait ball in the field.

“Soak some corn or wheat or oatmeal, make a bit of a ball out of it, and bury it into the soil. Use a flag or something to mark the area, let it sit for a week or so, then dig things up,” he explains.

If there’s more than one or two wireworms per bait ball, there’s likely a population that could be damaging your crop.

Wireworms find their food by following carbon dioxide emitted from a plant and the type of material used in the bait ball is important. Too much green material will release more carbon dioxide than your crop plant, and may provide an overestimation of numbers, skewing your results.

There are other management tactics, other than seed treatments, Gavloski says. Anything you can do to get quick germination and early growth will assist with wireworm management. Seeding into warm ground, at the appropriate depth, packing the soil a bit, are all agronomic practices that may assist.

Problems can arise when farmers seed into cool soil when the seed sits for a long time, and early growth takes a while.

While wireworms aren’t as devastating as flea beetles or cutworms, damaged patches can amount to around five to 10 per cent of a field. This doesn’t sound like a lot, but projecting that kind of loss further along the season into harvest can add up. While scouting for wireworms, poor emergence patches are what to look for, and shredded leaves may also be visible.

“Dig around those damaged plants in those damaged areas,” Gavsloski says, as “there can be many reasons why things don’t germinate, so you have to sort that out,” he explains.

There are beneficial insects to look for while out scouting that eat wireworms, for example, stiletto fly larvae, which are very narrow and are almost transparent. They behave differently from wireworms, and if disturbed, stiletto fly larvae will wiggle around, like a snake. Ground beetles will also help out when they burrow into the soil and feed on a variety of larvae, including wireworms.

Watch the full conversation between John Gavloski and Kara Oosterhuis below:

 

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