Pest Watch

Be Wary Of Wireworm

Wireworm larvae, Image by Frank Peairs

If you’re out in the field this summer, you might hear a faint “popping” noise coming from your corn. No, it’s not the summer heat popping your corn off the cob. Instead, it may be a small beetle pulling the lever on its built-in ejector seat nearby. And, if you happen to spot one of these acrobatic arthropods flipping through the air, you might want to start checking beneath your feet for its less-charismatic offspring, wireworms.

WHAT TO LOOK FOR

There are several species of wireworm that damage crops, but many of the important ones look and act in a similar manner. Adult beetles are brown, oval-shaped insects and are typically ½ inch long. They’re called click beetles because if they fall on their backs, they will suddenly flip into the air with an audible “click” as they right themselves. These beetles emerge from the soil in early to mid-spring and are usually the only life stage people will see.

The female click beetle lays her small, white eggs singly in the soil, usually near host plants. The larvae hatch from the eggs after two to four weeks and have a pale-yellow appearance. As they mature, they develop a hard, jointed shell with red-brown coloring, and some species grow to 1.5 inches long. Unlike other crop pests, wireworm larvae may take several years to fully mature, spending all that time underground. Wireworms also pupate underground, and so, this stage is rarely seen.

DAMAGE

Wireworm damage is spotted early in the season with soils that remain damp having a greater likelihood of damage. Local pockets of stunted plants or gaps in rows will appear in areas of wireworm activity. Most of this damage occurs to the seeds, roots and other belowground portions of the plant. Any aboveground damage may be confused for cutworms. But, unlike cutworms, wireworms do not completely cut through stems, leaving them ragged instead. Fortunately, wireworm activity subsides as warm summer temperatures drive the larvae deeper underground. By the time they return to the surface late in the season, crops are too mature to suffer damage.

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MANAGEMENT

Because wireworms take multiple years to mature, fields with past histories of wireworm will likely have them over several seasons. This is especially true of fields previously used as pastureland. Most wireworm-management programs require action before planting in order to be effective, as there are no pesticides listed for wireworm postplanting.

Two to three weeks before planting, set up four bait stations per acre in fields where you suspect wireworms. Bait traps with ½ cup of a 1-to-1 soaked corn-wheat mixture and bury them 6 inches underground, covered with black plastic. After a week, collect the traps and check for wireworms feeding on the seed. If the average number of wireworms per trap exceeds one larva, treatment is necessary. Alternatively, dig up 20 columns of soil measuring 10 inches long x 6 inches wide from different areas of the field and treat if there are more than two larvae per 10 columns.

When possible, planting corn later in the season can avoid the worst damage, as the larvae retreat deeper underground when soil temperatures rise. Replanting affected areas can minimize the financial impact, but, benefits will vary depending on crop and timing. When needed, chemical agents, such as seed treatments (e.g., Lumivia, Poncho and Cruiser) or preplanting broadcast applications (e.g., Baythroid XL, Warrior II), are available.

So, if you see some of your plants getting nibbled on, don’t “flip out.” Replant for now and consider your options for next season. The wireworms will still be there and waiting for you.

FOR MORE INFORMATION

> Purdue University Wireworm Resources

> University of Nebraska-Lincoln Wireworm Resources

Write Scott Williams at Pest Watch, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or e-mail scott.williams@dtn.com.

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