Wireworms: What Are They and What To Do About Them?

Wireworms attack field crops, root crops and corn. There are several different kinds of wireworm species. The most damaging are:

  • Wheat wireworms (Agroites mancus)
  • Eastern field wireworms (Limonius agonus)

Very often their damage is confined to small areas in a field. Even so severe infestations can result in an almost total loss of crop.

wireworms attack corn, field crops, root crops
Wireworm – image via Flickr |Katja Schulz

What can you do about wireworms? In this article, we describe them, explain their lifecycle and share advice on preventing and controlling their predation. Read on to learn more.

Wireworms’ Appearance And Life Cycle

As adults, wireworms are very common beetles known as click beetles.

Adult click beetles are quite slim, very hard-shelled and a reddish brown color.

The adult harmless and is the only iteration of this pest that you will commonly see. You may have seen these around your garden and your home.

These beetles are so-called because they snap their thorax when held or alarmed.

The clicking sound may frighten away any predator intent on eating the beetle. It also allows the beetle to “jump.”

The adult beetles lay their eggs in the soil. These immature garden pests bugs grow entirely in the soil.

Female wireworm beetles lay several hundred very small, round, white eggs in loose soil. Female beetles do not lay their eggs in a cluster but scatter them out singly over a broad area.

When the eggs hatch, small 16th of an inch long white larvae with dark brown jaws emerge. They change in appearance quickly.

After a month their color becomes yellowish-brown, and they develop a hard, shiny exterior.

Next comes the wireworms stage. If you see wireworms on your plants, you will note that they are between a 1/4″ of an inch and 3/4″ of an inch long.

The wireworms are brownish yellow, slim and cylindrical with three sets of short legs.

Upon maturation, wireworms pupate.

It is very rare to see the pupa. If you find a soft, fragile 1/2″ inch long white creature in the soil that looks very much like a click bug, it’s a safe bet that it’s a wireworm pupa.

It takes quite a while for wireworms to reach the pupal stage. In fact, from start to finish, an individual may live three or four years.

Partially grown wireworm larvae overwinter in the soil, as do some of the adult beetles.

In the springtime, the adult beetles emerge. As the weather warms up, the females begin depositing their eggs in loose soil.

At all stages, wireworms stay underground and feed on developing plants roots, tubers and stems.

Mature larvae become pupae during the late, hot months of summer and transform into adult beetles just before fall. These adult beetles stay in the soil until the following late spring.

Click beetles produce one entire generation every two or three years.

Generations can overlap so new adults emerge every single summer and lay more and more eggs.

At any given time a wide variety of ages and sizes of wireworms, click beetles and larvae are present in the soil and on your plants.

How Do Wireworms Damage Plants?

Wireworms larvae live and grow in soil. As they mature, they eat the tubers, roots, and stems of growing plants.

The most damaging species of wireworms typically consume the roots of grasses.

For this reason, gardens and crops planted in grassy areas the year before are at higher risk of being attacked by wireworms.

These pests are most attracted to root crops such as potatoes and also small grains and corn.

If you are in the corn growing season, adult wireworms can damage plants in many ways. They may destroy plants before they even emerge from the soil.

Right after planting the seed, wireworms will eat the sprout as soon as it emerges.

If plants manage to get a little bit larger, wireworms will eat the portion of the stem hiding underground thus killing your plant.

If plants can attain a height of about 18″ inches, wireworms will tunnel among and feed upon the roots causing scars and damage.

If planning potatoes, wireworms can cause a great deal of damage.

They will destroy crops by tunneling through the individual potatoes and leaving them riddled with holes.

Luckily, wireworms are not very smart, and it’s easy to trick them into eating non-growing potatoes, thus saving your crops.

What Can You Do For Pest Management Wireworm Control?

Because it does take so long for wireworms to grow and reach maturity, it also takes a long time for the soil to be clear of them.

Without active control, wireworms can cause a great deal of damage for many years.

To control and eradicate wireworms is an ongoing, multistep process.

You’ll need to treat the soil before planting or at the time of planting. Once the crop is in the ground, complete control is not possible.

Even so, monitor the soil regularly and look for signs of wireworms in the roots and along the stems of your plants.

It’s best to do your monitoring when the temperature of the soil is a little over 45° degrees Fahrenheit.

The soil should be slightly moist. Dig down into the soil approximately 10″ inches turn the soil and look through it to see if you see any signs of wireworms.

Spread each soil sample to about 6″ inches thick and sift through it.

Repeat this with a minimum of 20 shovels full of soil from various locations in your garden.

If you find one wireworms in a shovelful of soil, you can estimate that you have a population of 20,000 wireworms or more for each acre of land you are planting.

If you find two or more wireworms within 10 shovelful’s of soil, you are likely to suffer quite a bit of loss.

This level of infestation justifies aggressive preventative treatment using a pesticidal soil drench.

If you want an organic means of control, try neem oil plant soil drenches.

As a general defense, introducing beneficial nematodes work as a defense against all manner of soil-dwelling pests.

Otherwise, speak with your County extension agent about appropriate soil fumigation for your location.

How Can You Prevent Wireworms Infestation?

Start by knowing what crops have been planted in your field in the past.

If grass has been planted, you’re likely to have a wireworm infestation.

As noted, dealing with this problem in advance of planting is far more effective than waiting until after you have planted.

Crop rotation can help reduce wireworm numbers. For example, planting alfalfa will reduce or eliminate wireworms in your soil.

If you can grow an alfalfa crop or another legume for a couple of years, you may be able to deal with the problem naturally.

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