Detect wireworms before it’s too lateUnderground, and often undetected, wireworms—the larval stage of the click beetle—can wreak havoc on cereal crops like barley.
Wireworms on the rise
Scott Meers, an insect management specialist for Alberta Agriculture and Rural Development (AARD), said there has been an increase in wireworm issues in Alberta, but it has not yet raised serious concerns.
“The impression basically is that wireworm issues have been increasing, not dramatically, but consistently over the past several years,” said Meers. “So it’s the sort of thing we’ve been seeing more of each year, but I don’t think it’s an epidemic yet.”
In the past, an organochlorine pesticide called Lindane effectively controlled the insects. However, Lindane was banned in 2004 as a result of concerns surrounding the hazards and environmental accumulation of the pesticide.
Since then, wireworm populations have been on the rise, as no new products have been registered that effectively eliminate them.
Dr. Bob Vernon, a research scientist and wireworm expert with Agriculture and Agri-Food Canada (AAFC), has conducted work to find new ways to reduce wireworm crop damage. Last summer, a cluster project was formed between AAFC and the Canadian Horticultural Council to develop new methods of wireworm control in root crops. However, Vernon said that part of the project involves developing strategies to eliminate wireworm populations as economic pests in rotation years involving cereal crops like barley and wheat.
“The idea here is to develop insecticide blends applied to wheat or barley seed to reduce existing wireworm populations in the field, as well as to kill the huge neonate wireworm populations arising in the cereal crop later in the spring and early summer,” said Vernon.
“By doing this, the threat to the cereal crop is removed, as well as the threat to subsequent rotational crops for the next two years.”
A large wireworm can kill two or more seedlings, feeding on germinating seeds and burrowing into stems. If a field is infested, it is likely to contain wireworms at all growth stages simultaneously. It takes three to four years for wireworms to reach their adult stage, feeding on whatever crop is available.
Soil temperatures of 10–20 degrees Celsius in the spring are ideal for wireworm activity. The worms retreat deeper into the ground in July and August as higher temperatures dry out the soil.
Wireworms cause more damage in crops planted in silty, medium texture, well-drained soils and soils that have been under continuous pasture for at least five years. Crops in newly broken sod are extremely at risk because they provide ideal conditions for click beetle egg laying.
Wireworms also love summer fallow, and damage is often more severe following a fallow year. Cereal crops like barley are especially susceptible to wireworm infestation.
“Establishment almost always happens in a cereal year,” said Meers. There are numerous visible signs of wireworm damage. Meers said that thinning of the crop is the first symptom of a wireworm problem. He added that yellowing of individual plants, damage just above the seed on the coleoptile and hollowed out individual seeds are also indicators of wireworms.
Wireworm damage is often mistaken for a seeder miss, a poor seed lot, dry growing conditions, cutworm damage or herbicide carryover. As a result, the problem often goes untreated, leading to even more damage.
There are chemical products available in Canada to combat wireworms, but they are all seed treatments. No easy solution exists to eliminate wireworms found in an emerging crop.
“Basically, you have to have an insecticide seed treatment to manage a wireworm issue,” said Meers. “You learn about the problem this year and then you plan your control or management for next year.”
The two wireworm seed treatments currently available in Canada are Syngenta’s Cruiser Maxx Cereals and Bayer Crop Science’s Raxil WW. Both control resident wireworms long enough for the crop to establish, but allow them to recover later.
“What we do know is that the current seed treatments are management treatments, they’re not actually killing the insect outright,” said Meers.
Digging will usually confirm the presence of wireworms, as long as you do so early in the spring when warm soil temperatures and germinating seeds are drawing them to the surface. If not, prepared bait balls, which produce carbon dioxide to attract wireworms, can be used to indicate insect presence.
The most important thing to remember when dealing with wireworms is that you have to be consistent year-toyear with your preventative treatments.
“Once you have a wireworm problem, you need to keep treating. Make sure you have insecticide-treated seed, because treatment from one year doesn’t take the problem away—they’re still there,” said Meers. “We can manage a wireworm problem, we can’t eliminate a wireworm problem.”
Prevent and manage wireworms:
- Delay seeding slightly so that the crop will emerge quicker.
- Seed as shallow as possible into a warm, moist seedbed.
- Because wireworms actually have to feed to ingest the insecticide seed treatment, plant loss will occur, so increase seeding rate by 15 to 20 per cent to replace losses.
- Include a legume or pulse crop in rotation with cereals and oilseeds. This will gradually reduce wireworm populations, as these crops are more resistant to wireworms and are not preferred for click beetle egg laying.
- Use insecticide-treated seed since there is no way to treat for wireworms in an emergent crop, and damage is often noticed too late for reseeding.
- Mix 1 to 1.5 cups of oatmeal or wheat flour with two tablespoons of honey and up to half a cup of water until the mixture sticks together enough to make a ball.
- The balls can be placed directly in the ground, or tied up in a mesh bag (old socks or cheesecloth work well, too).
- Bury the balls in four- to six-inch deep holes and mark them with flags.
- Place roughly 20 evenly spaced bait balls per acre for best results.
- Check the bait balls for wireworms every four to five days.
- Make sure there are no competing sources of CO2 (green manure, living plants, etc.) within one metre of the bait. If wireworms are sufficiently fed, they will not be attracted by the presence of a new food source and will not go for the bait.