One of the most damaging insect pests in North America has been lurking in small numbers for decades, spending most of its long life in the soil waiting for an opportunity.
That opportunity has arrived. Wireworm armies are massing and the war on prairie crops is underway. (Click here for a wireworm life cycle graphic in PDF format)
“It’s under the soil’s surface, where we don’t see it until it shows up in lost yields or missing plants,” says Bob Vernon, Canada’s leading wireworm researcher and one of North America’s senior scientists that study the pest.
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“And it is often blamed on something else, for a while.”
A few Canadian farmers and agrologists have been burying bait balls filled with flour since 2004 and sending what they find to Vernon and his colleagues at Agriculture Canada’s research centre in Agassiz, B.C. Syngenta and Bayer now provide the bait kits.
“Once you start to look, you find the problem, and it’s growing,” Vernon told Agri-Trend’s Farm Forum in Saskatoon last week.
Farmers had kept wireworms under control since the 1950s with a few basic chemicals and techniques. That ended in 2004 with the loss of lindane, commonly known as Vitavax seed treatment. Wireworms weren’t an issue when lindane was applied to cereal seed once every four years.
Canada, along with the rest of the world, has been restricting the use of organochlorines such as lindane.
“It was overused, becoming wind-borne in soils and showing up in lakes and other places it shouldn’t be,” said Vernon.
The loss of those organochlorine pesticides has resulted in a rising wireworm population.
“It could be that reduced tillage practices are also contributing to improved habitat for the pests,” he said.
These seed treatments had long half lives and restrained the pest for up to 30 years.
They were replaced by a group of chemicals called neonicotinoids.
When used as a seed treatment, these chemicals cause resident wireworms to stop feeding and become moribund for long enough that a crop can become established. However, they do not stop the pest from continuing through its reproductive cycle. As a result, populations continue to expand.
In Canada, 30 species of wireworm can economically damage agricultural crops and pastures.
The most common in Western Canada are hymnodies bicolor and selatosomus destructor in dryland fields and limonius californicus in irrigated fields.
The pests arrive as cereal-loving click beetles that lay their eggs in a wheat field, creating a pest problem for the next three to five years . First season neonates turn into second to fourth season wireworms that remain underground eating seeds, roots and lower stems.
The pests, which are attracted by carbon dioxide gassing off as seeds become seedlings, come to the surface to feed on the crop before it can be established.
Farmers in eastern Washington state’s Palouse area are seeing damage so severe that they are abandoning some fields. Even the new seed treatments are failing to control the problem.
“As the effect of lindane wears off in the soil, we are seeing a growing problem across Canada, from canola and cereals to potatoes and fruit like strawberries,” he said.
Vernon and colleague Wim van Herk have developed a combination of products that is proving effective in controlling the worms. However, they are not registered for use in Canada for wireworms.
Van Herk said they found that applying neonicotinoid, Syngenta’s thiamethoxam, (Cruiser Maxx) and a low volume of a phenyl parasol, (BASF’s fiprinol) kills the worms over time. The strategy causes the worms to suspend feeding early in the season, providing the necessary control that farmers are seeking.
Vernon feels the combination will meet the needs of growers and regulatory authorities.
“But it’s not registered,” van Herk said.
“Fiprinol is off patent and needs someone to champion its registration and submit it to (the Canadian Pest Management Regulatory Agency).”
He said about one teaspoon of fiprinol per acre will kill wireworms for up to three years.
“The thiamethoxam has some other positive effects on plant growth, vigour, that we have observed as well. So the two products not only provide control, but improve crop yields. This is one of those true win-wins that you rarely ever see.”
Bayer’s Raxil WW, imidacloprid, is another neonicotinoid that is used to control wireworms. Synthetic pyrethroids such as tefluthrin (Force), bifenthrin (Capture) and lambda cyhalothrin (Matador) repel worms, but none kill.
Syngenta has plot trials underway in Washington for new products that are successfully controlling the pest in the region’s most heavily infested dryland fields.
Vernon and van Herk are also testing higher rates of neonicotinoids and new compounds, but they also hope the fiprinol and thiamethoxam seed treatment will be licensed in Canada before the wireworm problem becomes chronic.
