BANFF, Alta. – A canola pest caught prairie farmers off guard last spring and summer.
“The diamondback moth was a major concern this year,” said John Gavloski of Manitoba Agriculture. He talked about the 2001 outbreak at a seminar in Banff about crop pests.
The diamondback moth does not generally overwinter in Western Canada. It is assumed that most of them enter the country on southern winds from the United States.
In normal years, the moth is not detected until late May or early June. But this year there were strong, sustained winds from the south in early spring.
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That led to reports of moth sightings at Saskatoon and Yorkton, Sask., by May 10 and a few days later at Carman, Man.
“The numbers that were showing up this early in the season were really disturbing us,” Gavloski said.
Insecticides were sprayed in late May, but some fields had already been eaten to the ground and had to be reseeded.
Normally, pheromone-baited traps go up in June to determine infestation levels.
Gavloski said farmers need better advice on when and if they need to take action against this pest, especially if there is a repeat of early infestations.
“You don’t want to spray after the damage has been done,” he said.
When to start spraying is a judgment call.
The insect is most damaging at the larvae stage, eating the first leaves off seedling canola, but it may continue to feed on developing buds and flowers. The flowers abort and seed production is lost.
Researchers have established threshold levels for spraying when canola is in the flowering and budding stage, but the moths were so early this year they attacked seedlings.
Preliminary research shows seedlings can recover from what might appear to be severe damage, Gavloski said.
Many farmers overestimate the degree of damage and may spray when only about 15 percent of the leaf is gone.
However, while affected leaves take on a lacy appearance, a seedling can survive with few ill effects even at 25-33 percent leaf damage.
On more mature crops, Gavloski suggests spraying if there are 100-150 insects per sq. metre when canola is flowering, or 200-300 insects during podding. He suggests pulling up a single plant, shaking it over a vehicle hood and counting the larvae that cling to the plant.
