Wireworms could be a significant problem this spring – partly because of population increases and partly because of economics.
The immature click beetles are attracted to carbon dioxide produced by seedling germination.
In the past, producers often controlled the insects only on cereal grain and perennial grass, but the prairie grain wireworm is now known to have a taste for other crops as well, including alfalfa, clover and broadleaf crops such as canola, chickpeas, lentils, flax, potatoes, sugar beets, corn and sunflowers.
Agronomists and entomologists recommend treating fields on which the insects have been found in recent years.
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The wireworms are the larval stage of the insect, which lasts four to 11 years. During that time, the insects feed on living plant tissue and humus when necessary.
After the larvae emerge from eggs they need to eat within four weeks or they will die. Surviving insects then hibernate five to 25 centimetres below the soil’s surface.
Scott Meers of Alberta Agriculture said 30 species of the insect live in Canada, but the prairie grain wireworm is the big problem.
Saskatchewan agriculture ministry entomologist Scott Hartley said the insect population has been increasing since the pesticide Lindane was banned earlier this decade.
“Often producers thought they had a plant nutrition issue, but after adjusting for that, over two or three years, they realize it was the wireworm cutting into production,” he said.
“Wireworm used to be known for being spotty in the field – small patches. Now we see some of those small patches being 30 or 40 acres. It could be easy to mistake that for a lack of nutrients being available to the crop.”
Research in Alberta indicates wireworm damage can range from a few percent to more than 50 percent.
The insects prefer medium textured soil rather than heavy clay or light textured land.
Larvae feed on newly germinated plants and young stems, chewing up stem tissue but seldom cutting them off completely. The insects don’t eat plant tissues. Instead, they use enzymes to dissolve plant material, releasing nutrients useful to the bug’s growth.
Central leaves may wilt or turn yellow while outer leaves remain green. Eventually the plants fail, creating an appearance of poor germination or plant health.
In potatoes, plant tops seldom show signs of infestation, but insects burrow into tubers, creating pathways for disease and downgrading the crop.
Nichole McKenzie of the federal Pest Management Regulatory Agency said wireworms will return to the soil surface in late August to feed on potatoes, with damage often doubling every three weeks until digging.
As summer progresses, wireworms move deeper into the soil where it remains cool and moist.
Hartley said seed treatment is the only way to control wireworms.
“Even with cutworm you might get an opportunity to observe a problem, treat and reseed a shorter season crop. That isn’t the case with wireworm. You need to treat if you think there is a problem.”
Wireworms are well known to be a problem in pasture and hay land converted to grain production.
Calvin Yoder of Alberta Agriculture said high grain prices and the poor economics of cattle production are causing many producers to switch from forages to grain or oilseeds.
“You need to treat seed for wireworm for at least two years after that,” Yoder said.
Meers said trapping wireworms can help alert producers to their presence, but Bob Vernon of Agriculture Canada in Agassiz, B.C., said there are no established economic thresholds.
Placing whole potatoes in the soil in early August will attract the worms, as does burying flour or oatmeal in holes 10 to 15 cm deep at any time of the season.
The bait should be evenly spaced, with about 20 stations per acre.
Soil can also be sifted through a screen to find the worms after digging 15 cm deep samples.
However, researchers say not every one found will be a prairie grain wireworm. As a result, samples should be captured, along with damp soil, so that they can be correctly identified.
Weather drives wireworm activity – cool damp conditions will bring them near the surface, while hot dry weather will push them deeper into the soil.
Thimet will be available for chemical control of wireworm in potatoes and sugar beets until 2012, when it will be withdrawn.
Bayer’s Poncho is available for corn. Cruiser 5FS is available from Syngenta for wheat and barley.
Cruiser Maxx is available for edible beans and soybeans, but only commercial operators using closed systems can apply it.
No product is registered for other crops.
Crop rotation between highly susceptible cereals and less affected plants is recommended. Sugar beets on a four year rotation that doesn’t include potatoes or onions will reduce damage in beet crops.
Agrologists suggest that a well packed field will help prevent movement by the insects because they move slowly through compressed soil.
The insects can be very damaging in very dry soils and these should be avoided until rain is assured.
Vigorous growth in fall seeded winter wheat and rye show greater recovery from wireworm damage.
Hartley said while current seed treatments are effective in protecting crops in the season they are applied, they appear to do little to eliminate the problem, so proper agronomy practices are required to reduce overall populations.
