Traps to be set May and June in fourth trial season of integrative pest management for wireworm

“The problem is the solution.” Famous words from permaculture guru Bill Mollison. A phrase that sounds paradoxical. Yet, isn’t all great wisdom?

In recent years PEI has experienced a growing problem that has cost the potato industry millions. Three introduced species of European click beetle began to spread aggressively. Up until this time the populations had remained isolated to a small area on the south shore.

Like many introduced species that enter a new environment lacking their natural predators, European click beetles became invasive. It’s not the beetle that is of concern so much as its larvae, commonly known as wireworm. They bore holes in root crops like potatoes, carrots, and beets, as well as low lying crops like strawberries. The holes render crops unmarketable and allow pathogens to enter, reducing shelf life by increasing chances of rot.

Dr Christine Noronha, an integrated pest management specialist with Agriculture and Agri-Food Canada, had a few theories on why the problem has grown in severity. For one, residues from potent insecticides banned years ago are only now starting to breakdown, reducing barriers to both beneficial and troublesome insects. Milder winters also allow more overwintering larvae to survive into the next year. With larvae remaining in the soil for up to five years before emerging as adult click beetles, farmers may not have been aware of increasing populations until numbers became so great that beetles began to migrate to other locations.

Wireworms move vertically, not horizontally, in the soil  and this is one of the most challenging aspects when it comes to management, Noronha said. Insecticides applied to the soil surface or as seed treatments only paralyze the worm to protect a crop, but once out of paralysis it remains in the soil, and approved insecticides are only effective on potatoes. While tillage can be used to bring worms to the surface where they can be eaten by birds, the hotter drier summers we’ve been experiencing force wireworms to retreat even deeper into the soil. Cover crops like mustard and buckwheat are unfavourable to wireworm when incorporated into the soil. However, this practice comes at the cost of removing land from production for up to two seasons. In most farming operations, crop rotation is already common practice, but for small producers and home gardeners forfeiting growing space for a season or two is not ideal.

Taking into account the limitations of cover crops and insecticides, Dr Noronha looked at the problem from various angles to develop an integrative three-pronged approach to management. She understood the third prong must be addressing female click beetles that lays eggs in spring. This led her to invent a trap to reduce female populations. The design is simple: a solar-powered spotlight attracts beetles into a cup where they die in a solution of water, dish soap, and either salt or eco-friendly antifreeze. The cup is surrounded by a cage that prevents other beneficial insects like carabids from entering the trap. The traps are now being mass-produced by Growing Forward Solutions located in PEI.

While other traps using pheromones have been developed, they only attract males. As Dr Noronha said, you can trap all the males you want but it only takes a few to reach the females and continue the wireworm life cycle.

In the first trial in 2015, a single trap caught up to 900 beetles with 40 to 50 percent being female. In 2016 and 2017, the trial field was cover-cropped with mustard and traps revealed lower populations compared to 2015. This summer will be the first year potatoes will return to the trial field, with traps being set this month until the end of June.

Given the worm’s five-year cycle, Dr Noronha said that it will take several years to gauge the effectiveness of the traps. So far, she is very happy with the results, having seen a big drop in populations of click beetles since trials began.

Here lies the wisdom of Bill Mollison’s famous words. If “the problem is the solution”, then we don’t have a click beetle problem, we have a deficiency of predators to this introduced species. In creating a trap that catches females before they lay eggs, Dr Noronha has created an artificial predator. This month as lobster fisherman set their traps, farmers and home gardeners battling wireworm can also celebrate their own kind of setting day.


About Tara Callaghan

Decisions are not Tara’s friend. For this reason her passion cannot be reduced to one subject. She has always needed to write, keeping a journal since she was in the single digits. Her career began studying ecology and creative writing. From there she went on to study Landscape Architecture, working professionally for the last 10 years. More recently she launched Little Victory Microfarms; a small farm in Charlottetown and New Glasgow, PEI. With her mother, they grow a wide variety of fresh herbs and vegetables for market and wholesale.
While continuing to feed her passions for designing landscapes and growing food, Tara also feeds her passion to write though an eclectic blog and articles for Salty.

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