SWD showing strong resilience Destructive insect
hasmade earlier appearances and producedmore generations during warmer years.
By Judie Steeves R
esearchers at the Summerland Research and Development Centre updated members of the B.C. Cherry Association in November at the annual science forum, on current research into cherry pests and diseases and strategies for improving fruit quality, including spotted wing drosophila.
SRDC entomologist Howard Thistlewood, who specializes in research into management of SWD, warns there appears to be a winter form of it that is stronger than the summer one.
Although few survive winter, he told cherry growers the insects seem to be adaptable, with earlier appearances in the past four years and more generations being produced in warmer years such as 2015.
Last year there was the earliest full bloom since 2003 and it was warm from February to July, which created ideal conditions for insect growth. He noted that the latest ripening cherry cultivars suffered the worst attack by SWD last year.
“Sugar levels seem to be critical to the timing of the attack,” he noted. High brix levels and the flies were both early in 2015.
It’s important that non-crop host plants where SWD builds up, such as raspberries, be removed or the pest controlled in them, he warned. Overwintering occurs both in and out of the orchard, and it appears to be linked to winter temperatures and pesticide use.
SRDC insect biocontrol researcher Joan Cossentine is ready to field test a micro-organism which she hopes will help in control of SWD.
She has been working to find a biocontrol for SWD, so growers could turn to a softer control strategy without the use of pesticides, and she has found
or early July and seven to 10 days later it lays eggs which hatch into maggots in five to 10 days. They feed inside the fruit for about five weeks before the fruit drops from the tree. It overwinters in the soil as a the pupa, which can stay in the soil for a year or two.
It’s native to Eastern North America, but was detected in Washington State in 1980 and was discovered on the Southwest B.C. coast, on Vancouver Island and in the Fraser Valley in 2006, and in 2013 it was found in Prince George.
JUDIE STEEVES Howard Thistlewood.
a microbial pathogen that causes a fungal infection in SWD. In the lab, she says the fungus Metarhizium brunneum Petch causes SWD mortality in its adult or fly form. The flies require contact with the fungal spores to acquire an infection and the mortality occurs about a week later, as a function of temperature and dose, she explains.
Ideally this fungus wouldn’t be applied by spraying the canopy because it is non-specific. Instead, she’s hoping to find a bait that will successfully lure SWD to a station where they would contract the fungus.
However, as yet, researchers haven’t found a good attractant for SWD.
Next pest spotted
The latest invasive pest hovering near the borders of the Okanagan Valley, apparently might have got a toehold last year. A single female apple maggot was discovered in an area of West Kelowna, although they were unable to find any but that single one anywhere else. Ministry of agriculture entomologist Susanna Acheampong reported that the apple maggot is closely related to the cherry fruit fly and looks very much like that other invasive pest, with black and white striped wings.
As well the snowberry maggot looks similar. “You need an expert to tell them apart,” says Acheampong. Hosts include apples, crabapples and hawthorn, plum, cherry, peach and pear.
The adult, or fly, emerges in late June British Columbia FRUIT GROWER • Spring 2016 21
In the province’s commercial apple production areas, monitoring with traps has been ongoing for 20 years during the season, but last year was the first caught in one of the hundreds of traps set out throughout the Okanagan and Similkameen.
If the maggot got established here production costs would increase as would pesticide use and there could be additional impacts on apple exports. It’s not expected there would be an impact on the cherry industry.
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