Monitor Populations & Soil Temp to Gauge Wireworm Risk
By: Shane Thomas
April 1, 2013
There are about 30 species of the pest that are of economic impact in Canada with the genus hypnoides bicolour accounting for more than 70% of the wireworms pest population. These small, orange larvae of the click beetle can range from less than one cm in size to 2.5 cm in size depending on the genus.
The lifecycle of these pests starts with the overwintering click beetle laying eggs in May and June in cereal fields. These eggs hatch into wireworms which then become “resident” wireworms for three to five years, moving nearly a meter down into the soil profile. They are attracted to germinating seeds by sensing the C02 emitted by the germinating seed, and aren’t terribly choosey about what they eat. Wireworms will feed on wheat, barley, durum, peas, lentils, potatoes, and they will even eat canola, making them a difficult pest to manage for using rotation. To top it off they can survive without feeding on plants for up to two years by feeding on soil matter.
Wireworms will feed not only on seed, but will also feed on plant roots and the crown of cereal plants later on in the season. Each worm can gobble up two seeds a season — with a population approaching 1.5 million per acre being reported, this feeding can become very detrimental to a farm’s bottom line.
Soil moisture and temperature have a big impact on how active wireworms are and the resulting damage. They do not become 100% active until soil temperatures reach about 10 degrees C in the spring, and prefer soil temperatures in this range. As soil warms, they begin to be driven down deeper into the soil where it is cooler. They also prefer adequate moisture, too much moisture or too little decreases their activity.
Damage is identifiable due to bare patches and inconsistent emergence across the field. Confirming wireworms requires digging up plants randomly across the field, and because many fields have wireworms, it’s important to monitor populations. Using a bait ball is an easy, cheap and effective way to monitor populations — click here for more on how to make and use them.
The first plan of attack on wireworms is using high germ, vigorous seed combined with proper seeding depth to get the crop up out of the ground and growing well as fast as possible. A proper seed-applied blend of fertilizer can enhance vigor as well. A seed treatment that is a combination of an insecticide and a fungicide rounds out the plan of attack. Syngenta’s Cruiser (thiamethoxam) seed treatment and Bayer’s Raxil WW (imidacloprid) are insecticides in the neonictinoid family that will knock the wireworms out for six-weeks or so, but this is only after feeding on a couple seeds, so be aware that you may still see some feeding damage. Please note: death occurs in less than five percent of wireworms from these treatments, so populations are not decreasing.