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Difficult to get a count on wireworms

New BASF seed treatment should pack a terminal punch

New BASF seed treatment should pack a terminal punch

If there was such a thing as carefree wireworm days they definitely have become numbered as registration of a new, effective seed treatment developed by BASF has received final registration.

Why it matters: The presence of wireworms when sampling, even at low levels, is a potential cause for concern, experts say.

BASF announced Oct. 19 it has received registration for Broflanilide, its newest active ingredient, from Health Canada’s Pest Management Regulatory Agency.

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“Broflanilide is the first IRAC Group 30 available in Canada,” says Chris Hewitt, BASF brand manager, seed treatment. “It’s a powerful insecticide in two new unique products: Teraxxa F4 insecticide and fungicide for cereals and Cimegra for potatoes and corn. Both products will be available to Canadian growers for the 2021 season.”

Teraxxa F4 is the first seed treatment in 16 years — since Lindane was removed from the market — that can claim to actually control the pest that appears to have increased in numbers across Western Canada. It can cause serious economic losses in a number of crops including most cereals, potatoes and other horticultural crops.

Broflanilide, the active ingredient in Teraxxa F4, is a novel mode of action, says Hewitt. “Its unique mode of action directly impacts wireworms by eliminating them upon contact, providing true control and providing growers the advantage needed to ensure proper establishment and ultimately produce yield,” he says.

Lindane, which was taken off the market in 2004, was very effective on both resident and neonate (newborn) larvae, controlling 65 to 70 per cent of resident larvae and 85 per cent of neonate larvae. Other effective insecticides, used primarily in potato, that are no longer available include Temik, Dyfonate, Furadan and Counter (corn).

Filling the void after Lindane were a number of seed treatments developed within the neonicotinoid insecticide family. The neonic products were good. They were quite effective at protecting seeds and seedlings from resident larvae; however, mortality is low. The neonic insecticides — which themselves are under registration review right now — essentially paralyze wireworm larvae during a critical seedling establishment stage. However, the larvae survive and later become active. Neonicotinoids are completely ineffective on neonate larvae.

“A big part of the increase in pest numbers is due to persistence in the insect’s life cycle,” says Hewitt. “The pest can live in the soil for as long as six years, depending on conditions, and can survive without food throughout our long winters. Wireworms can also survive during rotations to non-host crops and be ready to feed again once your rotation returns to cereals.”

Crop and yield losses add up

How bad is the wireworm situation out there? Farmers across Alberta, Saskatchewan and Manitoba, along with portions of the United States, have suffered a surge in wireworm populations and subsequent crop damage, according to university researchers. There aren’t official surveys, but anecdotal evidence from growers, entomologists and researchers across the West points toward a growing population that is only likely to get worse.

Wireworms, the larvae of click beetles, typically live three to five years, a life cycle that exacerbates the problem. First, click beetles move into a field from surrounding permanent habitats — grassy ditches, pastures and undisturbed field borders — and lay eggs. That cycle repeats each year, with additional eggs being laid every year. Meanwhile, the first wireworms are growing and maturing underground. When that generation reaches adulthood, the pests begin laying their own eggs, and then the growth takes off exponentially.

“All of a sudden, the population can just explode,” says Bob Vernon, a research scientist now retired from Agriculture and Agri-Food Canada. “This is starting to happen, and it’s a real concern.”

“Increasing populations are leading to greater damage, from shredded stems to thin stands,” says Ruhiyyih Dyrdahl-Young, BASF technical representative for the northern Great Plains in the United States. “A single large wireworm can eat two or more germinating seedlings, and there is no solution after planting. Farmers need to be proactive and plan ahead when managing the pest.”

Extremely large populations — it’s possible to have more than one million wireworms per acre, Vernon says — can destroy the majority of an emerging crop that was seeded around 1.5 million seeds per acre.

Farmers can face a loss of more than 50 per cent of seedlings, and those that survive may be stunted, further reducing yield in a field already taking a hit.

In the last five years, it has become more common for damage to be severe enough that the surviving crop can’t compensate by producing more tillers, forcing growers to replant the field. That’s added seed, added time, added labour and added wear on the equipment.

“It can be an added expense growers have to incur,” says Dyrdahl-Young. Wireworms can cause other management headaches by making fungicide application much more difficult. Ongoing feeding can cause plants to mature at different rates and different heights. Areas that are bare or have patchy growth are also at a higher risk for weeds all season — and even into the next year. A farmer may have to choose whether to make additional applications or leave part of a field more susceptible to weeds.

Pests are difficult to count

Since wireworms move up and down through the soil profile, it can be difficult to get a handle on just how heavy an infestation may be at any point in a field. Some research over the years suggested applying control measures (seed treatment the following season) if traps revealed about 32 wireworms per square metre. However, the poor and variable accuracy of sampling methods, in general, questions the reliability of action thresholds. The current thinking by some entomologists is the presence of wireworms when sampling, even at low levels, is potential cause for concern.

If producers are interested in getting some idea of pest numbers, fairly simple homemade traps can be installed in fields.

Baiting the insect pest at low soil temperatures or during inclement weather will reduce the effectiveness of most baits. Also, in fields with high levels of organic matter, such as recently plowed sod fields, wireworms might not leave the green manure to move to baited traps or bait balls. In other words, a low wireworm catch in various baits can still mean that high wireworm populations are present.

Potato sampling

Whole potatoes buried in marked locations in a field in the spring, or from early- to mid- August, will indicate whether wireworms are present. Bury the potatoes 10 to 15 centimetres deep, and then dig them up after a couple of weeks and examine them for wireworm tunnels. Monitor fields each year.

Soil sampling

To sample for larvae, sieve the soil through a screen. Mark out areas 50 cm by 50 cm and sieve the soil to a depth of 15 cm. Repeat in different areas of the field to determine an average number of larvae per square metre. Sampling during germination will increase the likelihood of finding larvae feeding on seedlings.

Bait balls

Bait balls can help in the assessment for the presence of wireworms, but they do not necessarily indicate the density of larvae and are not always foolproof. Larvae may not be attracted to the bait if they have sufficient feed already.

Here’s how to make and monitor your fields with bait balls:

  • Gather your ingredients: oats, water and nylon (or other porous material). Form a ball with the oats and water and place in the nylon and tie with a knot.
  • Dig a hole approximately one foot deep, place bait ball, cover with soil and mark the location for ease of assessment later.
  • Ten to 14 days later, pull bait balls from the ground and assess the number of wireworms present.

In spring, begin trapping fields two to three weeks prior to seeding, as soil temperatures warm up. Although there’s no magic number of wireworms that constitute a problem, the presence of multiple worms indicates a yield-limiting issue. You can also use bait balls in the fall as a means of determining the severity of the wireworm problem for treatment the following year.

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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