Corn: Wireworms

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Description
2. Life History
3. Damage
4. Scouting Technique
5. Action Threshold
6. Management Strategies
7. Updates on Corn: Wireworms
8. Related links...

Description

Wireworms are larvae that are 7-35 mm long, cylindrical, copper-brown-coloured and hardened (see Plate 9). Adult wireworms are beetles that have the ability to flip themselves upright when placed on their backs, making an audible click as they do, giving them their name "click beetles."

Plate 9. Wireworms have long, cylindrical, copper-brown, hardened bodies. They affect many crops, usually when following grassy crops in the rotation.

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Life History

Wireworms take up to 6 years to develop from egg to adult, spending most of their life as larvae. They overwinter as larvae in the soil below the frost line. When soil temperatures warm in the spring, the larvae move to the surface to feed. Due to their long life cycle, the larvae can damage several successive crops, feeding on the roots of weeds, grasses and crop plants. Once soil temperatures become hot and soil moisture decreases, the larvae migrate downward and may be difficult to find later in the season. When it is time to become adults, the larvae migrate back to the surface, pupate, and the adult emerges to mate and lay eggs in grasslands or weedy areas.

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Damage

Wireworms are most active during the months of April to June and occur most often in fields that have little disturbance. The larvae attack roots, seeds and germinating seedlings of many crops such as corn, soybeans, wheat, edible beans and potatoes. Non-uniform growth or gaps in the stand may be due to wireworm feeding on germinating seeds. Injured seedlings appear stunted and wilted with leaves sometimes becoming purple or blue at the tips. The problem is usually worse in the second year out of sod after high grass-weed pressure, or when cereals are frequently in the rotation. They are also generally more prevalent in sandier soils, especially on the knolls.

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Scouting Technique

Wireworms should be scouted in mid-April, prior to planting. To scout for wireworms, a few weeks before planting, establish two bait stations per high-action site in each field. Dig a hole at each station, approximately 15 cm wide and 5-8 cm deep. Choose one or two high-action sites in the field (i.e., sandy knolls, heavy grass infestations). Bury a nylon mesh bag with 1 cup equal parts untreated and soaked corn and wheat or freshly cut potatoes at the bottom of the station. Mound the soil over the bait to prevent standing water. Return to the stations a few days before planting to sift through the bag contents to record the number of larvae found per station.

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Action Threshold

One wireworm per bait station.

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Management Strategies

Seed treatments should be used in fields with a high wireworm incidence or following grassy sods. Seed treatments will protect germinating seed but tend not to protect the seedlings. In-furrow or banded insecticides at planting are recommended if populations exceed the action threshold. No rescue treatments are available. For insecticide recommendations, see OMAFRA Publication 812, Field Crop Protection Guide. Control grassy weeds in crops previous to corn. (Order OMAFRA Publication 812)

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Updates on Corn: Wireworms

• Field Crop Protection Guide - Publication 812
  • Wireworm

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Related links...

• Insects
• Corn

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