Spotted Wing Drosophila: Lessons From 2012
November 20, 2012 
Note: The Autumn 2012 issue of The Bramble, the newsletter of the North American Raspberry and Blackberry Association (NARBA), included reports from across the country on the most recent issues with the spotted wing drosophila. The
following is a sampling of the information gathered, courtesy of NARBA; for more details, go to www.raspberryblackberry.com.
Michigan
As of Sept. 10, reports Michigan State University Extension agent Bob Tritten, “I have had a number of phone calls and emails from fall red raspberry growers who are finding larvae or ‘worms’ in fruit. In some cases, growers have discovered the fruit infestations themselves and many other growers have discovered wormy fruit when they have had calls from customers with wormy fruit.” A record number of spotted wing drosophila (SWD) have been caught in traps, indicating that pressure is building rapidly from this pest. Some growers have had just a few adults caught in traps, but when they checked for infested fruit, have found a good number of fruit infested with larvae. Michigan State University small fruit entomologist Rufus Isaacs is calling this the “Fall SWD Tsunami.” They are recommending that growers trap for this pest to know when it first arrives and whether spray programs are working, and check for infested fruit using a simple salt solution method. Management recommendations may be found at www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdf.
Pennsylvania
There is a new set of four full-color fact sheets on SWD available online at http://extension.psu.edu/vegetable-fruit/blog/2012/spotted-wing-drosophila-fact-sheets-completed-and-online. They are written with Northeastern growers of the most susceptible crops (raspberries, blackberries, day-neutral strawberries, and cherries) in mind. Part 1 briefly summarizes the concern surrounding SWD, and illustrates in detail the differences between SWD adults and other local fruit fly species. Part 2 discusses the life cycle of SWD in detail, and explains how environmental conditions and nearby crops can affect presence and numbers of SWD. Part 3 covers how to monitor for SWD adults in fields, and SWD larvae in fruit, and how to store and ship samples should identification from others be needed. Part 4 discusses cultural practices for minimizing populations, and chemical options to provide effective control for growers of susceptible crops.
Washington
(From Tom Walters, Northwest Washington Research and Education Center): Our major perceived threats on berry crops are to raspberries and late-season blueberries. Numerous processing raspberry and processing and fresh blueberry loads have been rejected due to SWD. Diligent conventional growers can usually manage the problem, but it is a real burden economically and logistically: lots of extra labor and pesticides to apply products on a tight schedule. Our organic growers are in real trouble, as they don’t have much to work with.
Oregon
(Tom Peerbolt, Peerbolt Crop Management, OR): Here are a few of the main points as I see them, after three seasons of experience coping with SWD: The danger zone seems to be from late July through the season’s end (give a week or two either way). The main economic cost is one or two extra insecticide applications from mid-July through the end of harvest.
Smaller growers, farms with mixed crop fields of smaller size, and organic are all at much greater risk due to less equipment, fewer tools, and more breeding sites close to vulnerable fruit. There’s a trend away from planting late-season crops and concentrating on the earlier ripening cultivars to avoid SWD. This will most likely accelerate.
While larger growers have a good handle on the insecticides and the spray intervals, their main weakness right now seems to be coverage. SWD hang out in the shady, humid interior and aerial or other overhead applications have trouble getting into the interior of plants. Sprayer types and techniques are an area where there’s now a lot of attention. Trellising, pruning, and field layout are evolving to allow easier passage through the vulnerable fields during harvest and allow for better coverage. This season quite a few cannon sprayers were used/sold and folks who have overhead sprinkler systems are starting to use “mistigation” (insecticides through overhead sprinklers).
Massachusetts
(Nate Nourse, Nourse Farms, MA): We are now pruning fall raspberries to remove the low side canes with berries. We are also pruning summer raspberries to end their production this week. Our intention is to have a two-week break from raspberry harvest that enables us to use insecticides with long preharvest intervals. While we found larvae in both raspberries and blueberries, we had no complaints from our customers.
Our weekly insecticide treatments on all berries were one part of our success. We closed the PYO raspberries on Tuesdays and blueberries on Wednesdays to allow the use of 24-hour PHI insecticides. Our pickers are good at removing soft and juicy berries, picking into two-quart buckets. Our packers get a second look as the fruit is packed into baskets. We fear that we are going to run out of insecticide options during the fall harvest. We hope other options will be available before this happens.
For a report a recent SWD Eastern Working Group meeting, go to the next page of this story.
Eastern Working Group Meets
Note: The following report, written by Debby Wechsler of the North American Raspberry and Blackberry Association, first appeared in the Autumn 2012 issue of The Bramble.
On September 20, I attended a meeting of “eFly,” the Eastern SWD Working Group, which brought together about 40 people (with another half dozen people attending remotely) to discuss current SWD infestation, research, and management in Eastern states, start to develop an impact statement for SWD, and begin to prioritize potential next steps in research, Extension, public education, and regulations.
Those attending were growers, researchers, Extension, marketers, and others from many Eastern states. Peter Shearer from Oregon State University brought a report from the West Coast, where SWD has been an economic problem for the past three to four years, and a multistate consortium of institutions is in the middle of a $5.6 million grant to work on this rapidly expanding invasive pest.
A few of the points that were brought out during this meeting:
• The two most widely used baits for SWD monitoring traps are a vinegar solution, and a yeast/sugar solution; it seems the yeast/sugar solution may work better, but is messier. It was noted, these are both fermentation products, yet this is a fly attracted to ripening fruit, not overripe berries. A new alternative lure combining several chemicals is in the works and looks promising. Better monitoring methods are being researched. The key will be to develop monitoring or models that alert when to start control measures.
• Alternate wild hosts for SWD in the East include pokeweed, bush honeysuckle, buckthorn, wild cherries, and elderberries. We still don’t know where they overwinter. Control of the population may be an impossibility, and it is hard to get good spray coverage. Control methods that focus on creating a chemical/physical barrier that prevents the flies from laying their eggs may be the best strategy. Work is being done to find biocontrol agents such as predatory wasps.
• There appears to be variation between different raspberry/blackberry varieties in how susceptible they are to SWD. Breeding resistant varieties may help long-term.
• The SWD experience in the East differs from that in the West. The hot dry summers suppress SWD in the West; here, higher humidity helps them thrive, and rains wash off sprays. Growers are finding that once-a-week sprays may not be enough.
The group developed a long list of avenues for further work, from mating disruption, increasing pesticide efficacy with feeding stimulants, and finding new control materials to figuring out the best way to dispose of damaged fruit and greater outreach to small growers and backyard gardeners. Now, the job is to prioritize among them, seek funding, and coordinate the work of different institutions to maximize effectiveness.
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