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Wireworm: hard to control and on the rise

Without Lindane, there’s very little that cereal growers can do to control this pest

Wireworms ruin many cereal crops, and they’ve been on the rise since the federal government banned lindane for use as a pesticide in 2004. Lindane killed the bugs outright says Dr. Bob Vernon, a research scientist with Agriculture and Agri-Food Canada (AAFC), and since its banning “there is really nothing that will kill them.”

“Wireworms are the larval stage of click beetles,” says Vernon. And because they have such a long lifespan, “they’re different than a lot of other pests out there.” Depending on the species, some wireworms can be in the soil nine or 10 years, says Vernon, before “they complete their life cycle.”

While there are over 20 wireworm species across Canada, says Vernon, three are really prevalent on the Prairies: Selatosomus destructor (a large species, at “an inch and a quarter long in its final stage, and they can live for several years in the soil”), Hypnoidus bicolor (“less than a half inch long in its final stage, and their life cycle is between two and three years”), and Limonius californicus (a species “which seems to be increasing in scope and numbers in the Prairies, especially southern Alberta” and is generally associated with irrigated land”).

All three types of wireworm are a concern, but with californicus, says Vernon, “fields have been completely wiped out, fields like spring wheat or barley.” This means populations are extremely high. This is also usually happening in minimum till fields, where there is typically a higher moisture content, maybe allowing californicus to build up in those fields, says Vernon.

Wireworms get a foothold in your fields through the grassy areas surrounding crops, says Vernon. “Wireworms are always in grass.” Click beetles — the bugs that wireworms eventually grow into — move into fields to lay eggs. Once eggs are laid, “you have them there for four years,” says Vernon, the lifecycle length of a californicus wireworm.

Controlling wireworms

In the past, Lindane would clean up the fields every time it was used (usually every three years or so). Since, there have been “no insecticides registered that would actually kill wireworms.” Populations continue to increase.

Neonicotinoids do not kill wireworms, says Vernon, but seeds treated with it would “intoxicate the wireworms for one to two months,” at which time the crop can establish. But after that intoxication period, the wireworms will just continue to live out their lives. “And in some cases, we’ve found populations increasing with the use of neonicotinoids,” says Vernon. With really huge populations of wireworms (in some fields in the Prairies) these treatments don’t always help, says Vernon.

“My biggest worry is, because we’re not killing them in the field, eventually they are going to produce adults in that field, and not just in the grassy area next to the field. Those adults will lay eggs in that field of wheat, for example, which we haven’t had for decades and decades, due to Lindane.” This is how habitat increases, and we’re starting to see this destruction in some fields already.

Also worrisome is the fact that weather doesn’t seem to matter when it comes to wireworms.

There are no insecticides registered, says Vernon, “that will completely solve the problem.” Vernon and others at AAFC have been testing various seed treatments and insecticides to see what’ll help, but that process is ongoing.

In terms of non-insecticide practice, it really depends on your farming constraints. Planting brown mustard in a field has been found to help reduce some wireworm populations, but farmers would have to sacrifice a crop that year to see if it makes any difference.

If you’re concerned about a particular field, says Vernon, “you can go out and dig around a bit to see if you can find any wireworms — especially if the soil is about 10 degrees” (when wireworms are active on the Prairies). If you think wireworms are present, “you shouldn’t try to plant that field early. Hold off planting those fields where you suspect wireworm problems to be and plant those fields last.” This is because insecticide seed treatment will degrade if there is a post-planting bout of bad weather.

“New products are tested every year,” Vernon says, but right now it is “status quo in terms of products available.” And you’ll see the problem increasing.

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