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Wireworms in Small Grains

by Dr. Ian MacRae, Extension Entomologist

I've received reports of wireworms in small grains this season - not surprising this year given that wireworm tend to be more active in cooler conditions. There are several species of wireworms in the Red River Valley and although they're usually neither a frequent nor wide-spread problem in the RRV, when they do occur, damage can be quite significant even leading to a total field loss.

The larval form of click beetles (put an adult on its back, it'll flip right-side-up with a 'click' sound) wireworms are ½" to 1 ½" long, smooth, slender and have a relatively hard, yellow to brownish shell; if you hold them between thumb and forefinger and 'roll' them, they feel hard and, you guessed it, wiry. They overwinter in the soil, burrowing down 9"-24" in the fall. In the spring when soil temps rise above 50F, they become active and move near the surface where the larvae feed on roots and planted seeds. As temperatures increase, the larvae will move deeper in the soil and become less of a problem. Feeding damage appears as gouging and furrowing in the root.

Wireworms are difficult to control and rescue treatments are ineffective, if not impossible. Seed treatments and at-plant insecticides can be used as a preventative, but there's little that can be done after symptoms become apparent. Because wireworms live as larvae in the soil for 3-4 years, wireworm populations tend to build over time if not treated. Consequently, areas that were in non-rotated or non-tilled cropping systems tend to have higher wireworm populations (e.g. CRP or any field in which grasses were growing). Preventive measures should be taken if there was evidence of wireworm populations in a field the previous year or if the field is coming out of an at-risk system (e.g. CRP). If re-planting a damaged field, seed treatments or at-plant insecticides should definitely be considered.
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