How to Control Wireworms

You’re not alone. Wireworms are a huge problem, and the problem is getting worse. A simple search of wireworms will let you know all about them, so I won’t spend too much time on it. But know these basics:

1. Wireworms are the larvae of Click Beetles. Therefore they are grubs, not worms. 

2. Click Beetles are above ground and lay their eggs at the base of plants all summer.

3. The larvae live for four years and feed on seeds, and tender plant tissue. 

4. Their damage can look like thinning out of plants or poor germination. Their damage usually kills a plant that remains standing (unlike cutworms which sever the stem). 

5. They are a dark cream to orange colour with a dark head. Their six legs are tiny but near the head. 

6. When you bend them in half they will snap. 

Now, let’s get straight to it: here are the solutions.

Step 1:

First, you need to know that there is no silver bullet for wireworms. They require multiple mechanisms to reduce their impact in your garden or farm. So, step one of many is to till. 

Click here for this article in video form: Controlling Wireworms by Gardening with Bugs

Even if you are a “no-till gardener” please read on. Just by knowing why we till you may be able to use that knowledge and do your own thing. We till to control wireworms through two mechanisms. One is it exposes them to birds and other predators; the other is it physically damages or kills them. 

To kill them, you likely need to employ a machine to mechanically till the soil. We know this is effective because Washington State University completed a study looking at pros and cons to tilling, and found they measured significantly lower numbers of invertebrates (good and bad) when they tilled. Now, for some of us that is a negative. But the study went on to show that if your crop is susceptible to wireworms (for example) the reduction (over all) of bugs in the ground meant greater yields were achieved. 

Now, I have to mention susceptible crops – because wireworms alone aren’t the end of the world. They are only problematic in large numbers and in some crops. Crops you’ll want to till are:

1. Any bed that was grass, sod or grains last season or two seasons ago.

2. Ahead of any grain crop

3. Ahead of any tuber crop (carrots, potatoes…etc)

4. Ahead of any lettuce/sunflower crop

5. If there is a history of major wireworm damage. 

The mechanism of exposure is as simple as it sounds. Under grasses (where wireworms prefer to be) they are protected. When we stir up the ground and loosen the soil all their predators can find them much more easily. And just exposing one often results in repeat predation; once a bird finds a wireworm it is likely to come back to feed on more. 

So, tilling before you plant a susceptible crop is recommended if wireworms are present. 

Step 2: 

Add a defence. The predatory mite Stratiolaelaps scimitus (Stratio) is usually applied to most gardens/crops anyways – to feed on soil pests like fungus gnats, and thrips pupae, but they eat most soft bodied pests. And they are very successful at controlling the first stage (instar) larvae wireworms (the smallest ones.) 

You might be tempted to skip this step because it’s the bigger larvae that do most of the damage (and typically the ones you see) but do not skip this. Wireworms are larvae for four years in the ground. So if you can control the first years, and each year after that, you are on your way to success against wireworms. 

It is said “the best time to plant an apple tree is 20 years ago.” Well, the best time to apply Stratiolaelaps scimitus to your garden/field is 4 years ago. So get it done immediately after tilling. And if you don’t till, get Stratio in now. Without tilling, it only needs one application for…well… ever, in most places. 

Step 3:

Trapping. This is fairly simple. Give them something to eat that isn’t your crop. The trick is: they are attracted to carbon dioxide releases. In the winter cold and summer heat they travel deep and then come up when the grasses start to grow and put off carbon dioxide. You can similarly attract them by germinating potatoes or grains. 

For potatoes, simply burry them. When the tuber wakens the wireworms will strike and you’ll have wireworms all over the potatoes. Remove the potatoes. Some people will place potatoes around a bed, others will just pop a few in randomly. 

It is believed that wireworms do not travel far, and so trapping has to cover a lot of ground to be successful. I have seen exposed ones travel quite quickly, and have found no actual study on their movements. My guess is the denser the soil the slower they move. Regardless, trap as much as you feel is necessary. 

Another great tool (and maybe less expensive) is to germinate grains. Grab some from the store, dig a little trench and lay the grains. Cover it and let them germinate. Again, you’ll have to go back to this spot and dig up the wire worms. 

Some farmers use “bait balls.” These are made up of wheat flower and oats. You just add enough water to form a ball, put it in a cheesecloth and burry it with some cloth sticking up. You can retrieve it by the cloth and pull up a bunch of the wireworms that crawled inside. 

What to do with them? It may be easiest for you, and bring you peace-of-mind, to toss them into soapy water or some other way to kill them. I fully support this. However, let me remind you of the second mechanism of tilling for wireworm control: exposure. If you have a place to put the wireworm infested potato or grain/dirt/wireworm combo, do so. Like on a tarp on your driveway, for example. If they crawl back into your garden, this doesn’t work. But if predators like birds go to town on the meal you left them, they will certainly stick around to look for more. More wireworm predators equals more future wireworm predation. 

Step 4:

Met52: Met 52 is not labeled for wireworms. And, as far as I can tell, the new formulation might only be labeled for greenhouses. So I am not officially recommending this. I am unsure why it is not on the label, since Agriculture Canada showed it was successful in controlling wireworms in potato fields in PEI. However, it was expensive and was not a benefit to the farmers. But, if this is something you need for one of the labelled purposes, know that it will also do well at suppressing wireworms.

Met 52 is now called LALGUARD M52 – produced by Lallemand. It is a fungus called Metarhizium brunneum (formerly Metarhizium anisopliae) that infects and kills pests. However, I will warn you that this is a broad-spectrum biocontrol agent. So while it will kill your target pests, it will kill everything else. While some of you might love that idea, note that broad-spectrum mechanism result in the same “pesticide cycle.” That is, the first thing to come back is the pests – but, without the predators – so you have to keep applying. 

Step 5:

Clean-up. The same study that looked at the success of Met52 against wireworms found that a cover crop of mustards had some impact on returning levels of wireworms. The reason is twofold. One: they don’t like mustard plants, and so they won’t build up there. Two: When rain hits a mustard leaf it picks up a compound that is noxious to many soil dwelling creatures. So there is some deterrent effect as well. 

Be cautious with mustards. Some are considered weeds and some are even invasive. Talk to a local farm store about which kind to use. I plant “white mustard” which is the one grown for the edible seed. And yes, I cut it down before the seed pods are ripe so it doesn’t self sow. 

I plant mustards late in the fall for an overwintering crop. In most years this works well. One year, they died in a quick cold snap. When they don’t die (here on the west coast) they flower in spring before other crops are typically planted. So it provides a great habitat while the rest of the farm is still waiting for spring. 

Step 6:

Trapping the adults. Adult wireworms are Click Beetles. They lay their eggs at the surface each year. You can try to control them at this stage, but there is nothing out there that seems to have much of an effect. Your best bet is the new trap created by the same researcher who did so much of the wireworm research in PEI: Christine Noronha of Agriculture and Agri-Food Canada. The trap is called the “NELT,” and uses light to trap the adult beetles. The cost appears to be about $30 each. Unfortunately, I don’t know how well they work. But considering one study looking at pitfall traps vs pheromones traps found that pitfalls caught more, I think this mechanism (using light) has the opportunity to be the best trap. 

Step 7:

Rotate your crops. You should always do this, and for a variety of reason. Click Beetles have preferred egg laying sites. Those larvae will be in the soil for 4 years. So if you plant a grain, attract the beetles to lay eggs, but successive years are crops that are not susceptible to wireworms, you’ll hardly run into much of a problem. And understand that the crop you might want to grow is not the best for your growing situation. So always match the plant to your location and other factors, including pests. 

Step 8:

Grow naturally. When you can, avoid using any broad spectrum bio-control agent, chemical or soap/detergent. In a natural soil you will have all manner of predators ranging from ground and rove beetles, spiders, nematodes, and soil mites. The longer an area remains in a natural state the greater the balance you can achieve. But, we’re not here to leave it in a natural state: we’re here to garden and farm. So, when you can, ensure that you are growing for bio-diversity and healthy soil and you’ll get some benefit out of a more balanced growing area. 

Since the pandemic more people have turned to gardening by reclaiming parts of their yard. So much of these new gardens were built on what was previously lawn. So the interest in wireworm control is at a new high. The most important thing to do is recognize the great risk associated with gardens previously covered in sod. Till it hard and apply Stratiolaelaps scimitus and consider trapping for wireworms and planting crops that wireworms will not prefer. If you are a commercial farmer, do not plant a wireworm susceptible crop the first year unless you can absorb the cost of Met52 and engage in all the steps above. If you can plant an alternative crop, and use the steps (not including Met52), you’ll have a better chance at success the second year. 

I have to again stress the importance of the predator mites stratiolaelaps scimitus. Commercial growers put this in as soon as plants sprout to control fungus gnats. Arborists use it to control black vine root weevil and other weevils in landscapes. Greenhouses use it to find straggling spider mites that have gone to ground after clean-up and again to feed on thrips that pupate in the soil. Farmers use it to control grubs (wireworms) maggots (larvae of fly species) and other pests that lay their eggs in the soil and feed on plants. So, whether you have trouble with cabbage maggots, flea beetles, nematodes, weevils or thrips, you should have Stratiolaelaps scimitus in your soil. It is native to North America and Europe, so there are no restrictions where it can be used. In a healthy potted plant or in a natural landscape one application can have a permanent affect. There is a list of places you can get them here: https://appliedbio-nomics.com/find-a-distributor/