A potential new wheat pest has appeared in southern Alberta and other regions of the Prairies. So far, wheat head armyworm numbers are low to moderate, but researchers expect them to be more active in August.
“Most of the sites we sampled in late July had up to three wheat head armyworm larvae per 10 sweeps, but some sites near Fort Macleod and Claresholm had as high as 14 larvae per 10 sweeps,” said Dan Johnson, a scientist at Agriculture Canada’s Lethbridge, Alta., research centre.
“Although the counts in 2000 indicate more than a 10-fold increase from 1999, so far the population remains below the levels at which control would be required.”
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No control products have been registered for this insect. The wheat head armyworm (Faronta diffusa) caterpillar is tan to green, with distinct white and brown stripes down its body length. It has a well-developed, rounded head with strong mandibles, which allow it to feed rapidly on grain kernels.
Young larvae crawl partially into wheat heads and occasionally the heads of other cereals, to feed from mid-July to late August. Light damage may be mistaken as grasshopper or beetle nibbling, said Johnson. Later in the summer, entire kernels are consumed.
“In warm weather, all the kernels on one head can be consumed by larger caterpillars in as little as one day,” he added.
The kernel-eating caterpillars grow through larval stages, increasing in size with each stage, before forming brown pupae that overwinter in the soil. They emerge as moths in the spring.
While the effects of tillage on the pupa are unknown, reduced tillage probably favors pupa survival and moth emergence. Warm, dry weather is believed to favor survival and growth.
If the caterpillars become a significant pest, it will mainly affect spring wheat, Johnson said, because winter wheat is harvested before the insects can cause significant damage.
In the United States, the pest may have two generations per year. In Canada, weather would probably limit the caterpillars to one generation per growing season, Johnson said.
Sex-attractant pheromones are known for this species, but have not yet been developed into a monitoring system.
Since the caterpillars feed mostly at night, collection during the evening or early morning is recommended for an accurate count.
However, Johnson said, some caterpillars will turn up in a net sweep during mid-day.
For more information about the pest, producers should contact Johnson at the Lethbridge Research Centre, 403-317-2214, e-mail, JohnsonDL@em.agr.ca; or Alberta extension crop specialist Rob Dunn, at 403-381-5351.
Photos can be viewed at the Lethbridge Research Centre website: http://res2.agr.ca/lethbridge/scitech/dlj/johnsond.htm.
