Wireworms are on the comeback trail and have officially re-emerged on the Prairies as the primary pest in cereals and other crops. Their resurgence comes after the elimination of products and practices that once kept them in check. This is one of the findings of a recently published study by Agriculture and Agri-Food Canada (AAFC) that paints a clear picture of the wireworm issue in Canada.
This revival is not welcome news for farmers. Wireworm larvae feed on germinating seeds, roots and young seedlings, killing plants outright, as well as creating wounds that are ideal for disease establishment. Wireworms aren’t picky either – they’ll munch on your malting barley just as heartily as your neighbour’s potatoes. Wireworms are also a difficult pest to manage.
“They have a very long life cycle. And it’s not a single species; it’s a complex of pest species that belong to different genera, and are very different from each other,” explains Dr. Wim van Herk, Research Scientist with AAFC. Van Herk co-authored the study with Dr. Bob Vernon (now retired). He says the fact that wireworms are below ground and often found in patches adds to the management challenge. “One section of field has them, and the neighbouring section does not. It can make fieldwork a nightmare.”
Farming practices impact prevalence
Van Herk has become an authority on wireworms since the study began in 2003 at the Agassiz Research and Development Centre in British Columbia.
“The last time any wireworm survey had been done nationwide was in 1943. We figured that with changes in agriculture over the past 60 years, it was time to take another look,” van Herk says.
The new study shows modern farming practices are having an impact on wireworm prevalence. For example, conservation tillage has resulted in higher soil moisture and increased food availability for the pest. The elimination of effective insecticides, such as lindane, is also contributing to increased wireworm survival rates.
Multiple species in one field
Wireworms at the larval stage can be difficult to identify. That’s where van Herk’s expertise comes in. He has collected more than 800 samples of larvae and click beetles (the adult form of wireworm) with the help of companies like Syngenta, as well as growers across the country.
“Samples have mainly come to us from the three Prairie provinces, but some were also received from Ontario and Quebec,” he says. “We’ve been slowly, year after year, compiling this massive data set.”
Once van Herk receives a sample, he puts it under a microscope or hand lens. “Based on whatever identification keys I can find, we figure out what species they are. And then we confirm our IDs with genetic analysis or barcoding.”
During the course of this identification work, van Herk discovered that multiple pest species are frequently found in the same fields where damage is reported.
Complete crop wrecks
“About half the time, the species we find is Hypnoidus bicolor,” he says. “It’s a very interesting species, in that we know virtually nothing about its life history or its ability to cause damage.”
According to van Herk, a species that is destructive today yet had very little mention in the 1943 survey is Limonius californicus. “We’re finding it more and more frequently, especially in southern Alberta. Wherever there is a complete crop wreck that Ted Labun [Seedcare Technical Lead with Syngenta] is called to look at, it’s virtually always this species.”
Van Herk’s survey shows that Limonius californicus is more prevalent on irrigated land and where the soil moisture is higher. “Dry soil is a weak spot for this wireworm species. The eggs desiccate due to lack of moisture and then they die,” he says. “So, if soil moisture increases either because of irrigation or because of tillage practices, there’s a likelihood you’re starting to preferentially select for Limonius californicus in your field, and the species builds up.”
In addition to holding moisture in the soil, minimal tillage along with continuous cropping also leads to more organic matter, which is a food source for the pest. Another tillage consideration is that less physical disturbance of the soil means there is less chance to mechanically control wireworm larvae, pupae and eggs.
So what advice does van Herk have for growers when it comes to controlling wireworms? “Our toolbox right now for managing wireworms is pretty limited,” he says. He hopes that will change with his follow-up work. “At the end of the day, what we want is solutions for managing wireworms that are effective on the different pest species in the different areas. So, we continue doing insecticide efficacy studies with Syngenta and other companies.”
Cruiser® Vibrance® Quattro is a cereal seed treatment from Syngenta that combines an insecticide with four fungicides for protection from wireworms as well as seed- and soil-borne diseases. In addition to using an insecticide seed treatment, scouting and monitoring are recommended management practices.
Van Herk is also working to develop new monitoring tools and non-chemical management techniques.
More samples welcome
Although the study has been published, van Herk says the work continues.
“I’m always interested in more wireworm samples. Every year, we learn new things about pest distribution and their habits. We’re grateful for any samples we continue to receive,” he says.
Growers can send samples to van Herk at his AAFC office. Simply put your specimen in a Ziploc bag with a little bit of soil. Providing details such as when and where it was collected, feeding damage observed, and your cropping system and field history is very helpful.
In the meantime, van Herk is grateful for the hundreds of samples he’s already received.
“Thank you for sending all those samples over the years,” he says. “That’s the only way we can get a good idea of what’s happening on the ground as to what species are causing the problems. We really appreciate it and welcome further contributions,” van Herk says.
Read more about van Herk’s study here.
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