CAROLYN TEASDALE
At left, a wasp-imitating adult Raspberry Crown Borer fans its wings, while at right, the insect in caterpillar form tunnels into the base of a cane.
Raspberry pest hard to detect
Degree-day data helps researchers determine how to develop effective spray strategy. By Judie Steeves
T
he Raspberry Crown Borer is difficult to detect until it’s too late to do anything about it.
In its adult stage it cleverly mimics
a wasp, even though it’s actually a moth, so unless you’re schooled in the differences you likely wouldn’t notice its presence in a field. In its larva stage, the insect bores
into the crown of your raspberry plants, out of sight, destroying your livelihood. So, with funding from the Raspberry Industry Development Council and Investment Agriculture Canada, researchers such as Carolyn Teasdale of E.S. CropConsult Ltd. are investigating other ways to detect this serious pest of raspberries in order to apply sprays at the critical time to control it. There’s only about a two-week
period in its two-year life cycle when growers have an opportunity to apply a spray against this pest, explains Teasdale. And, that period is not determined
by a calendar, but by degree-days of heat. Its rate of development through the year is based on the amount of heat there is. So, when the adult lays eggs under
14 British Columbia Berry Grower • Fall 2013
the leaves of raspberry vines, it’s critical to know when they hatch into small caterpillars and begin to make their way down the plant to the base of the canes, where they tunnel in, stressing and weakening them and providing an entryway for other pathogens. The rest of its life is spent in the
cane; 20 months of feeding on the raspberry plant, Teasdale explains, and at that point sprays are not going to reach them—if they could be seen. Last year, she says they studied the
timing of the egg hatch and developed a preliminary model of degree-days to that hatch, which is being tested this year. Ideally, this model would be available on a website for growers to access to know when each year it would be efficacious to spray for the Raspberry Crown Borer. They have three years of data, plus this year, on when peak flight of the
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adult stage occurs, and the model looks very solid, said Teasdale. There is also a pheromone trap for
the adults, but it is very labour- intensive to use and the pheromone is only good for a few days, which makes it too cumbersome for growers in the field. The eggs are small but not microscopic, so this September, Teasdale and Kristine Johnson will monitor fields for egg hatch so they can confirm the degree-days it takes to reach that point, when sprays would be effective. A couple of years ago, Altacor was registered for use against this pest, but the timing is critical. They hope this fall to be able to
create a model to compute degree days each year to egg hatch so growers will know when to spray. That will vary each season depending on what the weather is like through spring and summer.
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