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Wet Soil Conditions Favorable for Wireworms (05/14/20)

Wireworms are the larvae of click beetles (Coleoptera: Elateridae), and feed on most field crops grown in North Dakota.

Wireworms are the larvae of click beetles (Coleoptera: Elateridae), and feed ent.1on most field crops grown in North Dakota. Wireworm larvae (Fig. 1) are hard, smooth, slender worms varying from 1½ to 2 inches in length when mature. They are white, yellow or dark brown with three pairs of small, thin legs behind the head. The last body segment is forked or notched.

Wireworms prefer cereal crops like wheat, barley, oats, but will also feed on row crops like sunflowers. This week, agronomists scouting wheat fields in the north central ND observed wireworms feeding on newly planted wheat seeds and dingy cutworm larvae crawling around. The moist soil conditions are more favorable for wireworm development and larval movements within the soil profile. As soil temperatures start to warm up to 50-55 F in the spring, wireworms will move to the soil surface and become more active feeding on seeds / roots, and tunneling into stems / seeds (Fig. 2). Damage caused by wireworms include significant stand loss, reduce vigor and potential yield losses, especially in row crops like sunflowers. In recent years, wireworm activity has been increasing in severity, especially in no-till fields out in western North Dakota.

One of the ‘best’ pest management strategies against wireworms is knowing your field’s history for wireworm population levels. Wireworms have a long life cycle of 3-5 years as larvae in the soil. So, once they are detected at high densities, the field will remain ‘high’ risk for several years.

The second strategy for managing wireworm populations is insecticides and includes neonicotinoid insecticide seed treatments, or an in-furrow pyrethroid insecticide at plant. However, insecticides from both of these classes do not provide ‘adequate’ kill of wireworms in the field. Neonicotinoids only prolong morbidity periods (over 150 days) during which wireworms do not feed and pyrethroids are repellent and generally

nonlethal to wireworms. Some growers have resorted to using both insecticides, an insecticide seed treatment + a pyrethroid in-furrow, for wireworm control. However, recent research in sunflower has shown that there was no added benefit to using both insecticides, an insecticide seed treatment + a pyrethroid in-furrow, for wireworm control. Using both insecticides did not improve plant stand or increase yield compared to using either insecticide alone (Fig. 3). In addition, input costs were higher compared to using either insecticide alone. Other research suggests that blending could cause antagonistic effects by changing the behavior of wireworms. For example, wireworm morbidity induced by a nonlethal insecticides prevents sufficient ingestion of a lethal compound to cause mortality (van Herk et al. 2015.  J Pest Sci 88: 717-739).

Even though the current insecticide seed treatments and pyrethroids applied either as in-furrow liquids do not kill wireworms, both insecticide had higher plant stand establishment and higher yield than the no insecticide (untreated check) (Fig. 3). In addition, increasing rates of insecticide seed treatment, pyrethroid in-furrow did not significantly improve efficacy against wireworms or increase yield (data not shown).

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Best pest management recommendations for wireworm control include:

  • Use a registered insecticide seed treatments or a registered liquid pyrethroid in-furrow at the labeled rate to provide crop protection against wireworm feeding injury in spring.
  • Know your field history of wireworm pressures, since wireworms can live as larvae for 3-5+ years in the soil.
  • Control grassy weeds in fields to reduce attractiveness of field sites for egg laying by wireworms.
  • Increase seeding rate by 10-20% to compensate for wireworm stand loss.

Thanks to the National Sunflower Association for their support.

 

Patrick Beauzay

Research Specialist and State IPM Coordinator

                                                                                                                                                                                

Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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