No available insecticides can kill them and the one that can at least slow them down may be phased out. But biological control may have promise for managing wireworms, says an Agriculture and Agri-Food Canada scientist who has been researching the pest species.
“They especially love cereal crops and food crops like carrots and potatoes big time. Right now, they’re not killed by pesticides. So your only chemical control option for wireworms right now is your neonicotinoid seed treatments,” Haley Catton of AAFC in Lethbridge told the audience at FarmTech.
These seed treatments don’t actually kill wireworms. They just put them to sleep for a while so the crop can get established.
“That same population of wireworms will be back next year.”
There’s a potential phase-out of neonicotinoid pesticides, so that chemical control could be lost.
“Although I’m hearing from several companies that there are new products in the pipeline that they say will kill wireworms, but I don’t know more than that,” Catton said.
There are hundreds of natural species of wireworms across Canada. Most don’t pose a problem, but 20 to 30 species are pests that eat cereal and vegetable crops.
The pests on the Prairies are native species, unlike British Columbia and the Maritimes, where invasive species are the problem.
“The wireworms that we are dealing with here on the Prairies are very well adapted to our winters and our soils, and survive well in the grasslands, which is bad for us,” said Catton.
In Alberta, there are five to seven problem species. Anyone who has a wireworm problem and digs around in their field will find a variety of wireworm species.
Click beetle offspring
Wireworms only live for a year in adult form as click beetles. They have a bullet-shaped body and the hind end of their thorax has little hooks. They leverage the little hooks underneath the top of their wings to create tension and snap, making a click. Click beetles lay their eggs in the spring.
“We don’t know a lot about how they decide to lay their eggs, but where they do is pretty important for the future wireworm problems down the road,” said Catton.
Once the eggs hatch, wireworms spend up to two to seven years in the soil. They can overwinter and move up and down in the soil to feed on whatever crop is planted, but can survive without eating for a year if they don’t like that particular crop.
After they are big enough after several years in the soil, they pupate, come up in the fall and nest.
In any wireworm-infested field, there will be a variety of sizes of worms of overlapping generations and species.
“Some of them are hard to study because they live so deep in the soil,” Catton said.
Wireworms can create bald patches in a crop or even wipe out an entire field.
“If you have a dead patch in your field, it can be for various reasons. Maybe you have a chemical spill, or maybe it was a low, wet spot during seeding. But dig around the edge of that patch — there are still some live plants and that’s where you will find a wireworm.”
Searching for research fields
Catton is working on a long-term project called ‘Wireworms and beneficial insects in wheat,’ co-funded by the Western Grains Research Foundation and the Alberta Wheat Commission. There are also several Canadian Agricultural Partnership projects with other researchers collaborating. Another project involves looking for wireworm pheromones (sexual attractants) by using a monitoring tool to attract and track click beetles.
“In B.C. and P.E.I., they have pheromones that have been synthesized and identified for those species. Here in the Prairies, we haven’t identified the pheromones for those species yet.”
Catton is also leading the third and final season of a project to investigate wireworms, crop rotations and beneficial ground beetles. She is still looking for fields for the third year. They should be dryland fields with a wireworm problem less than two hours from Lethbridge and seeded to spring wheat in 2019.
“Because wireworms live for multiple years in the soil, if we trace the characteristics and population structures with the rotation it was before, it may give us insight into how to use rotation to at least slow it down a bit,” she said.
Catton only studies 12 fields a year because the study is so in depth. Her team samples the field by taking soil cores to about 10 centimetres down. The soil is packed into a container and taken back to the lab.
“Wireworms don’t like light or heat. We put the soil in this funnel and then we shine a light down on it. Wireworms don’t like the light, so they fall to the bottom of the funnel, where we have a little vial that will preserve them for us so we can identify them in the fall and winter months,” she said.
The adult click beetles are monitored using pit ball traps. The click beetles just fall into the containers where they are collected.
There are still no recommendations for management practices to control wireworms. Catton advised farmers to know their field history.
“If you have a wireworm field, it’s probably going to be patchy,” she said. “If you think you have wireworm damage, dig down around the edges of your live plants and see if you can find some wireworms. If you do, you can send them to us.”
If you want to be a participant in the 2019 field study, email [email protected]