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The Worrisome Lowdown on the Wiley Wireworm

Wireworm damage in root crops can be damned annoying and frustrating for the home gardener, and plain devastating to the commercial grower. Wireworms damage newly planted seeds, feed on the roots of young plants, and devalue root crops. Losses in potato production alone in the Lower Fraser Valley of British Columbia were estimated at between $500,000 to $800,000 reported in l994 (Vernon,1998).

And what exactly are these troublesome blighters? They are the larval stage of a beetle from the family Elateridae, and more precisely, our two BC villains are Agriotes lineatus and A. obscurus, commonly known as the click beetle. Like all critters, click beetles have a natural place in the scheme of things, eating leaves and acting like little compost heaps. The larvae are shiny, yellowish, semi crispy worms whose favorite foods are grass roots and seeds, decomposing and recycling as they go as the larvae are attracted to the carbon dioxide (CO2) produced by seeds germinating and growing root tips. The problems arise when we remove the sod. We now have some hungry creatures looking for a bite to eat, and believe me, if the only thing they can find to eat are your new crops, so be it.

This creates issues for handling newly cleared lawns or pastureland. A long term approach would be to starve the wireworms out by leaving the area fallow for a couple of years, letting them migrate back to the edges of the growing area. But they will migrate back as soon as there is food available.

A quicker solution, since we know that larvae will be attracted to the warm soil surface in spring, is to do some cultivating - exposing them to the dehydrating sun, dry soil and hungry birds. If we cultivate frequently, we can hasten the process of cutting down the population, while remembering that they can remain in the larval stage for six years or more. But as with all good things, there is a bad - over-cultivation is detrimental to the structure of the soil and hence the overall health of the soil.

A more aggressive act would be turning the area into a chicken or pig run (pigs getting special rave reviews in this area), since the larvae are a nutritious snack, even used, honey roasted, as a treat at a Washington state university. Why waste such a food source?

Following this treatment, there was a suggestion that planting the area in brassica (particularly mustards or oil radish) green manure crops and then turning this in might act as a repellant. There were suggestions that cropping the area with cole crops and squash might slow down the population rate, since these are not favoured foods. The University of Idaho had success with plowing decomposing rape seed green manure into the soil as a repellant. But where do the buggers go?? They are only being repelled.

There was some suggestion that fall planted crops suffered less damage than spring planted, and certainly in maritime BC, it is possible to fall plant potatoes with a good mulch.

But what if the area is already planted with foods that the wireworms will damage? Several sources suggested the "bait" method, where traps are placed with favoured treats, marked with small flags, and then dug up and -okay, no comments were made about how one picks the worms out of the trap, but I bet it would make a great treat hurled into the chicken coop. Suggested baits were chunks of potato (some have suggested that wireworms would walk a mile for a Red Norland), pieces of carrot or balls of moist oatmeal in old stockings, which could then be buried several inches under the surface of the soil, laid over with a piece of plastic bag and marked with a wire flag. This not only attracts the bugs, it gives you a chance to see how your infestation is ebbing and flowing. However, this is a tedious method for a busy market gardener.

Planting wheat between cultivated rows might help, as the wireworms are more attracted to grasses, and these could be used as sacrifice crops. Lettuce was also mentioned as a sacrifice crop. However, I imagine the wheat would have to be pulled and the root area cultivated to bring those larvae up, so that we weren't merely feeding the next generation of click beetles!

For those with a soil thermometer, there is the importation and use of nematodes. The nematodes used are a mix of Steinemema and Heterohabditus, applied in the spring, and after harvest in late summer or fall. Although this method is considered an affordable way to fight an infestation, without good observation of temperature and moisture levels, the nematodes have a hard row to hoe against those tough skinned wireworms, so timing and attention to the weather are everything.

Ongoing research at PARC Agassiz is assessing the efficacy of the insect fungal pathogen Metarhizium anisopliae as a biological control agent for wireworms, particularly for Agriotes obscurus (Kabaluk, 2001).

We may swear at the lowly and dastardly wireworm, but we should recall one thing. They may suffer from a preference for the same soil as we do - one that is high in organic matter - but they're the ones that made it that way, with their years of chewing and pooping. We need to slow down on the teeth clenching and get on with some thorough methods of converting grassland for field crops. We'll be glad we did - in about six years!

February 20, 2004
Robin Wheeler has written numerous gardening and environmental articles, and operates Edible Landscapes, a nursery on the Sunshine Coast dedicated to naturally grown popular and exotic edible plants.
1732 Pell Road, Roberts Creek, BC. Phone: (604) 885-4505. E-mail:

[We recently learned of Robin Wheeler's passing and want to acknowledge her valuable contributions to this web site. - Cyber-Help, March 2012 ]

See also: Down to the wire! Winning the war on wireworms

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