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Wireworms in Corn

Categories: GROWING, CORN
  • Wireworms can be a perennial problem in fields where damage is observed since they have up to a 6-year lifecycle.  
  • Fields at most risk for infestation were most recently Conservation Reserve Program (CRP) land, pasture, no-till, small grains, forages or had grassy weed pressure.  
  • Uneven stand emergence and gaps are good indicators of wireworm presence.  
  • With no in-season rescue treatments available, preventative management practices are important.   
Wireworms are an early season pest that may surprise growers as they are usually not considered a widespread threat. Although relatively uncommon, wireworms can become a severe and systemic problem in some areas. Included in this article are some ways you can detect and prevent an infestation in your fields.   

Identification and Life Cycle 
Hard-bodied, slender and ranging from a shiny white, yellow, orange or light to dark brown in color, wireworms are the larva of click beetles. They are named for their wire-like appearance, given their long, sleek bodies (0.5-1.5” in length), distinct head and coil-like indentations throughout.  

If conditions are conducive, wireworms may be the first pest of the growing season to impact a corn crop, which is why newly planted seed is most vulnerable to feeding. Corn is targeted by wireworms from mid-April to as far out as the end of June, where they reside in the first few inches of soil. As the season progresses and temperatures warm, larvae typically migrate deeper in the soil where they no longer cause damage to the crop.   

Once they emerge from their eggs, wireworms can remain in the larval stage for anywhere from 1 to 6 years, depending on the species. As they mature, they progressively cause more feeding damage and will reoccur within a field across successive crop years. Pupation then occurs in the soil in August or September and is about a month in duration. The pupa will emerge as an adult click beetle that will overwinter in the soil. In the spring, adult beetles lay eggs near grass roots or the roots of grass-type crops.    
Susceptible Environments 
The most preferable environments for wireworms have a history of, or currently contain, grass or forage species. Fields that were previously sod, grass cover crops, small grains, alfalfa, pasture, high residue/no-till, CRP land or even had high grass weed pressure are most susceptible. Cooler soil temperature and higher moisture are also favorable conditions for wireworms. Common instances of wireworm pest pressure often consist of planting corn early just before a period of cooler temperatures. The extended cool period allows larvae to stay closer to soil surface damaging crops for longer periods of time on already weather-compromised corn plants. 

Scouting and Management 
The largest indicator of a wireworm problem is uneven stand emergence, which can be observed most notably when scouting emerging to 5-leaf corn. Digging in the top 6” of soil in the weeks following planting, especially near grassy weeds or residue-heavy areas, is a way to gauge the amount of pressure, if any, that the field may experience.  

The use of bait stations is a common way to sample for larvae and determine risk prior to planting. This can be done by selecting five random areas of the field and burying a couple of handfuls of untreated corn and wheat seed about 6 inches deep. Cover these areas with black plastic and mark with a flag. It is recommended that these bait stations be established about 2-3 weeks before planting and dug up when it’s time to put seed in the ground. An economic threshold is estimated to be an average of one wireworm per station and then management tools should be considered.  

Although wireworms cannot be managed in-season via a rescue treatment, there are some preventative measures that can be taken to help mitigate feeding damage for corn that is at risk. Consider planting later for fields with active larvae populations, utilizing an appropriate seed treatment, and/or applying a soil insecticide pre-plant or during planting. For severe, postemergence infestations, a replant might be warranted depending on the impact on population.

For more information, contact your local Golden Harvest Seed Advisor.

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