This is the fifth winter for the SWD trapping program, trapping in early January 2015 saw surprisingly high numbers.
A slight sigh of relief was heard this year when berry growers had a small reprieve from the problematic Spotted Wing Drosophila (SWD). While the efforts of growers likely had an impact on the reduction of the pest, Mother Nature was also on their side in keeping the fly in check.
Tracy Hueppelsheuser of BCAGRI noted that SWD trapping results showed last winter’s populations were lower than previous winters and spring populations weren’t as high as in previous years.
“People didn’t tend to get blindsided by infestations,” Hueppelsheuser noted. “We don’t know what’s going to happen this spring, but we are trapping."
This is the fifth winter for Hueppelsheuser’s SWD trapping program, but results to date have been anything but consistent.
“It’s something different every year,” she said. “More years of experience of trapping [over the winter] will allow better predictability. We hope that winter trapping and spring trapping will give a better idea of spring [and summer levels of SWD].”
Trapping in early January 2015 saw surprisingly high numbers, but these volumes usually plummet at the end of January when there is a cold snap and SWD dies back. However, the amount of variables in studying SWD creates part of the mystery.
“There’s no doubt, we think they [SWD] prefer raspberry cane fruit over everything else,” Hueppelsheuser noted. “Summer raspberries have an advantage, they are early enough that [growers] can get the crop off before SWD can take over. Fall raspberries don’t have that opportunity, they are a much higher risk.”
However, Hueppelsheuser pointed to a benefit raspberries have over blueberries when it comes to SWD, that is they can be picked when pink and not at maximum ripeness to prevent added infestation pressures.
Other ways to keep SWD at bay aren’t new, but bear repeating: canopy management and pruning, 'pick early pick clean pick often', pest sprays and field sanitation and weed management.
“Prune in the off season and make it easier to get the machines through,” Hueppelsheuser said of canopy management. “It creates a dryer environment to keep SWD down and keep disease down.”
If picking is normally done every three days, Hueppelsheuser recommends picking every two days to tighten up the intervals in between picking.
A solid spray program and good field management go hand in hand. Keeping weeds down, maintaining clean equipment and using the appropriate spray at the appropriate time will help minimize SWD. That being said, some years the pest is out of control and it’s hard to know why.
Hueppelsheuser is working to understand this better. Different bait choices are being explored to determine what age fly is attracted to certain baits.
“We want to use a bait that’s going to catch young flies because those are going to infest your fruit,” she noted.
Trapping is the main tool to monitor SWD, but past trap and bait studies have focused on numbers of flies, regardless of the bait or age of flies.
Hueppelsheuser described the flies in human terms. It’s about finding the young female fly equivalents to human females who go out clubbing, work at the mall and eat entirely different food than their grandmothers.
“I would like other researchers and consultants to give that some thought,” she said of focusing on the types of bait used and age of flies being caught.
In addition to the bait studies and trapping, this is the second year of a long-term study to assess how the actions taken against SWD may be impacting beneficial insects.