One of the biggest challenges facing organic producers is the control and management of pests. The wireworm is a pest which poses significant economic losses to both conventional and organic farmers. Wireworms are the subterranean larvae of click beetles. They are a substantial problem worldwide and can cause severe damage to a variety of vegetable crops. Organic farms are particularly vulnerable as there are limited options for managing this pest organically, other than crop rotation. Few control products are available for organic growers.
Todd Kabaluk, the lead Agriculture and Agri-Food Canada (AAFC) researcher on Activity 21, estimates the wireworm’s economic damage to crops in Canada exceeds $20 million dollars. “Considering that wireworm loss in PEI potatoes alone likely exceeds $5M/year, you can extrapolate from that to each crop in every province and it does not take long to arrive at a remarkably high figure,” Kabaluk explains.
Wireworms are an exceptional barrier to organic expansion. Their presence in land not currently in production (organic or conventional) means that certain fields planned for future crops are already a battlefield. “There are wireworms out there in land that has not been broken… as soon as they turn it over and want to plant it, farmers find that it is infested with wireworms. It prevents them from further expanding. Organic growers are really in a bind, and infestations ruin [the] opportunity for the sector to expand in Canada,” Kabaluk says.
With a three-to-five-year life cycle, wireworm larvae can evade control efforts by staying underground and only coming to the topsoil to feed, though a greater understanding of their subterranean movements is needed. The research of Activity 21 targets wireworm larvae as well as the adult click beetles through a mixture of physical, cultural, and biological controls.
Researchers are looking to exploit a particular trait of wireworm feeding. Wireworms are attracted to carbon dioxide as their means of locating their food source. As plant roots respire, they emit carbon dioxide, drawing wireworms to them to feed on the roots and germinating seeds. Kabaluk and the AAFC research team have been experimenting with a strain of pathogenic fungus, Metarhizium LRC112, which is highly virulent to wireworms specifically. To attract the wireworms, they use carbon dioxide attractants, such as granules of rice or rolled oats which release CO2 as they decompose. These are inoculated with Metarhizium spores. By attracting wireworms with CO2 and fatally infecting them with Metarhizium in field trials, Kabaluk’s graduate student Aaron Thien has protected vegetables from wireworm damage, thereby significantly increasing marketable yields.
Kabaluk’s previous research has shown that adult click beetles also succumb to Metarhizium. Each female click beetle can lay hundreds of eggs at a time. Controlling the beetles before they have a chance to lay eggs represents an opportunity to limit the introduction of new wireworms into farmland.
Alongside the use of Metarhizium, researchers have been experimenting with combination applications of an organically approved fertilizer blend called EnterraFrassTM (EF), which acts as a desiccant on the wireworms, killing them by dehydration. Field trials using both the EF and Metarhizium LRC112 showed significant yield increases in a variety of crops grown where wireworms were present. “In field carrots, we were able to increase the number of marketable carrots by around 50%, and the marketable weight by 30% per hectare”, Kabaluk explains. These are impressive numbers, especially for organic growers.
In addition to the Metarhizium, Activity 21 has been looking at other biocontrol agents aimed at controlling wireworms at distinct stages of their lifecycle. Researchers have been able to identify a variety of sex pheromones that female beetles use to attract males. In collaboration with a private company, Kabaluk has developed a granular formulation for these pheromones. Distributing the substance on the soil surface when beetles are mating can prevent the click beetles from successfully mating, laying eggs, and producing more wireworms. Initial trials with this method, led by Activity 21 researcher Dr. Wim van Herk, have identified four pheromone formulations that successfully disorient and disrupt mating patterns of six wireworm species.
Some of the wireworm control methods being studied are less technical, while still yielding impressive results. Wireworms are an issue not only for root crops, but also for cucurbits and other ground-resting fruit. The wireworms come to the surface to feed and can damage fruit where it meets the soil. Researchers have been studying the use of plastic mulch with different thicknesses as a physical control method to act as a barrier between the fruit and the soil surface to prevent feeding damage (Figure 1).
Kabaluk’s research has been running concurrently with that of Dr. Michael Bomford from Kwantlen Polytechnic University, whose students have been leading field trials with Metarhizium LRC112 and other products. This data collection helps students learn about both research methods and alternative pest management techniques. Both Metarhizium LRC112 and the pheromone formulations have yet to be registered by the Pest Management Regulatory Agency, so the challenge of getting these products into the hands of farmers remains. However, results from this activity suggest that organic producers will have many new tools in their wireworm control toolkit in the years to come.
(OSC3) Originally published in Organic Science Canada magazine, Issue #5, Spring 2023
