Reducing wireworm risk
How will new research be applied in the field?
March 3, 2023 By Julienne Isaacs
Few Canadians know as much about controlling wireworm in conventional potatoes as Christine Noronha. An Agriculture and Agri-Food Canada (AAFC) research scientist based in P.E.I., Noronha has led three successive Canadian Potato Council/Canadian Horticultural Council cluster projects funded by the Canadian Agricultural Partnership – all focused on wireworm in potato.
The third project, which began in 2018 and will wrap up in early 2023, looked at various aspects of wireworm control, including rotation and alternative control strategies, insecticide efficacy and pheromone trapping.
One component of the project was a wireworm population survey in P.E.I. The first wireworm population survey on the Island was conducted in 2009, with successive surveys in 2012, 2016, 2019 and 2022, says Noronha. For each survey, adult click beetles were collected from 85 sites across the Island to get a sense of population makeup and dynamics.
“We were seeing populations going up, and in 2019 we saw a reduction. We think it’s because [growers] started to use mustard and buckwheat in rotation [around 2015], and the population reduced over time,” she says.
Taken together, the results of each component of Noronha’s research add up to significant gains in wireworm control.
There are very few insecticides registered for use against wireworms in potatoes in Canada. The neonicotinoid insecticide clothianidin saw its use restricted by the Pest Management Regulatory Agency (PMRA) in 2021 to a single foliar application in potatoes each season. Thimet 20-G, the organophosphate phorate, is still registered in Canada, but is highly toxic. Its use is also limited.
“There is an urgent need for novel alternative treatments that provide competitive tuber blemish protection and wireworm reduction with a safer human and environmental portfolio,” writes AAFC research scientist Willem van Herk in a new publication.
Noronha and van Herk were both involved in testing broflanilide, a Group 30 meta-diamide insecticide, for efficacy against wireworm as part of its PMRA registration.
BASF registered broflanilide under the trade name Cimegra in 2020 in potatoes and corn. Noronha says the product can be used in-furrow treatment.
Clothianidin worked by paralysing or intoxicating the insect, but didn’t always cause mortality. Broflanilide also targets the nervous system of wireworm larvae, but ultimately kills them, which can help reduce populations over time, says Noronha.
Pheromones are chemical substances released into the environment that signal an insect is ready to mate. Once chemists can synthesise an insect species’ particular pheromone signature, these unique chemical codes can play a fascinating role in monitoring and control.
Currently, synthesized pheromones are primarily used to attract and monitor populations, but they can also be used to disrupt mating, when so much synthesized pheromone is pumped into the environment that males can’t find females. There have also been studies that used pheromones to transmit pathogenic fungi to male click beetles, who would then transmit the fungi to females, and both would die, says Noronha.
Sometimes there’s cross-species susceptibility to a particular pheromone synthesis, she adds, but sex pheromones are typically unique to particular species because mating happens within species.
Along with van Herk and Gerhard Gries, an animal communication ecology professor at Simon Fraser University, Noronha has been attempting to crack the code of a particular European species of wireworm, Hypnoidus abbreviatus, that is present in P.E.I.
“It hasn’t been successful,” Noronha says. “With some species, we can’t find the pheromone. I’m going to try again, but there are other species that are in Western Canada [for which van Herk was] successful in finding the pheromone, and they work really well.”
Currently, there’s a big push to use a variety of crop mixtures in rotation with potato, says Noronha, both for their soil health benefits and potential to control pests.
Two good examples are mustard and buckwheat. Mustard is known to have biofumigation properties and can help reduce pest pressure in a field. Less was known about buckwheat, until recently.
In collaboration with her AAFC colleague Jason McCallum, Noronha has run several projects looking at whether buckwheat can suppress wireworm in potato rotations. In the lab, mixtures that included just 25 per cent buckwheat were enough to suppress populations.
“We found that [when] wireworms feed on the buckwheat, they stop growing and eventually die. What was really strange was that they liked the buckwheat–given a choice they’ll eat it versus other crops,” she says.
Last year, Noronha ran field trials looking at mixtures with varying percentages of buckwheat or mustard planted together with sorghum sudangrass, barley and other crops. The field trial results aren’t yet in, but the research is promising, says Noronha. If buckwheat shows the same efficacy in the field as it does in the lab, it could be a game-changer for East Coast farmers. Noronha is writing a wireworm management manual that will include suggestions for farmers on combining all of these techniques in an integrated pest management package.
Noronha’s wireworm project hasn’t been renewed as part of the industry-led newest cluster funding rollout, but given the significant strides that have been made over the last few years, the future is brighter for wireworm control.
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