Scouting for Wireworm

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Wireworm are below ground pests that primarily target corn and cereals but can also be found in soybeans, dry beans, forage crops and canola.  The risk of occurrence increases in sandy or silty soils and when the crop is planted early in a cool, wet spring.

All growth stages (larvae and adults) can be found in a field at the same time.  Adults lay their eggs in the soil during summer months.  The larvae stage is where damage occurs; this stage can last as long as six years depending on the species.

Wireworms overwinter as larvae or adults in the soil (below the frost line).  Once soil temperatures reach 10°C  or higher the larvae begin to move vertically in the soil profile, they move downward again when temperatures reach 26°C or higher.  Most active feeding is on seeds and roots between April and June, but can also be present near the soil surface in the fall.

Newly hatched larvae are white for approximately one month before changing into their more permanent state, at which time larvae range from 2 to 40 mm and have a hard, cylindrical body that is slightly shiny and copper in colour.  They also have a distinctive flat head and only three pairs of legs near the front of the body.

Adult wireworms are also known as “click beetles” and range from 8 to 20 mm (depending on the species).  They have a dark body (brown, charcoal, black) and taper at the base of the thorax.  An adult is able to turnover when put on its back, while producing a popping sound that earned its name: “click beetle”.


Begin scouting for larvae from April until the end of June and again in September, through to mid-October (before the first frost).  The best way to scout is with a bait trap, control thresholds start at one larvae per bait trap. 

Because wireworm larvae can live for up to 6 years in the same field, baits are an ideal method for monitoring. Baits are also easy to set up requiring only a shovel, soil thermometer, bag of flour, measuring cup and flags.  In the fall or spring when soil is moist and temperatures are just above 10°C, establish two bait traps per high risk area of the field (including sandy or silty knolls, areas with grassy weed patches, or areas where gaps in stand have been noticed).

Setting Bait Traps

For each trap, dig a hole approximately 15 cm wide and deep. Take 1 cup of all purpose flour and drop it into the hole. Bury the bait, breaking up any soil clumps and mound the soil to prevent standing water. Place a flag at the bait station to make it easier to find again and return seven days later to dig the bait out and determine the presence of wireworms.

One the wireworm per trap indicates the need for an insecticide seed treatment. Wireworm traps can capture both wireworms and millipedes. It is important to properly identify these two pests since insecticide seed treatments only provide protection against wireworms, not millipedes.

Other noticeable signs of wireworm damage include:

·         Root and seed – perforations and tunnels

·         Seedlings – stunting, wilting, yellowing and sometimes the death of the plant

·         Leaves – small notches (rare), purplish tips

·         Field – uneven plant height or stand thinning or gaps


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Sources: Grain Farmers of Ontario. Guide to Early Season Field Crop Pests. (verified May/15). OMAFRA.2014. Scouting for Soil Insect Pests in Field Crops. (verified May/15). Frank Peairs, Colorado State University, – see more  at: David Cappaert, Michigan State University, – see more at:
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. DEKALB and Design®, DEKALB® and Growing Knowledge® are registered trademarks of Monsanto Technology LLC, Monsanto Canada ULC licensee. ©2015 Monsanto Canada ULC.