May 1, 2014

SWD management viewed for Southeast berry crops

The impact of spotted wing drosophila is being seen throughout the United States. It’s a primary target for those involved with the management of insect pests in berry crops.

Hannah Burrack, associate professor and Extension specialist at North Carolina State University, has been on the frontlines of the SWD battle. She shared some of her experiences in January at the SE Regional Fruit & Vegetable Conference in Savannah, Ga.

Burrack was involved in the formation and development of the eFly Spotted Wing Drosophila Working Group. It is made up of scientists, Extension specialists and agents, fruit growers, marketers and educators working to develop management strategies for SWD, the rapidly spreading and increasingly significant pest of soft-skinned fruits.

The goals of the eFly group are to: facilitate coordination of SWD research, Extension and education activities; develop an eFly web page to coordinate regional information and connect with national information; rank and revise SWD research, Extension and education priorities; and maintain and update SWD impact statements in the eastern United States.

The working group has conducted extensive grower surveys to detect the latest SWD patterns in the region.

“We can get more tools for your guys, justifying pesticides and activities to deal with this pest,” she said. “We will be able to get support for those activities to get funds to do things that will help you deal with that pest.”

She said survey results would help identify research and Extension activities, and pinpoint those “we think are important.”

SWD’s impact on the southeastern part of the country has been well documented, affecting strawberries, blackberries, raspberries and blueberries.

“We are seeing some potential impact in day-neutral or later-season fall strawberries, with limited infestation in spring fruiting berries,” Burrack said.

North Carolina blackberries and raspberries experienced about a 15 percent loss from SWD damage in 2012, representing about $1.4 million in crop loss.

“Blueberry crop losses have been variable for us in North Carolina,” Burrack said of 2013 findings. “Most of our observations this year were during our processing season, so later in the processing period.”

She said there was not a reported SWD infestation in North Carolina grape vineyards, “although other parts of the Southeast have it.”

Burrack said blackberries and raspberries have been impacted by SWD more than other crops, because “they really do like to eat them.”

“Research going back several years ago showed they laid by far the most eggs in raspberries. They develop faster in raspberries because they are able to support more larvae than some of the other berries and other fruit.

“There have been similar numbers for blueberries over the last two years, but we haven’t seen the same differences in the infestation rate in blueberry and strawberry as we’ve seen in blackberry and raspberry, which is was a little surprising to us. We expected to see some differences there.”

Differences from previous year

Burrack said researchers in 2013 learned a few things more about SWD than they knew in 2012.

“We know this year, that in most cases, we have enough materials, enough insecticides to design rotational programs that will get us through a typical growing season,” she said. “In blueberries, when we employ those management programs we didn’t exceed our pesticide residue levels – our legally allowed pesticide residue levels using that management strategy – with the big caveat (2013) was a raining year, so we’re going need to do that hopefully in a year where it didn’t rain so darn much.
“For these materials, the residual activity appears to be less than seven days in pretty much all cases and certainly in rainy conditions; so a seven-day application interval probably makes sense for us,” Burrack said.

“We have baits we can put in traps that catch flies one to two weeks earlier than apple cider vinegar, which had been our standard bait we were putting in traps. And in some cases those baits may actually detect flies before we have damage in fruit. That’s something we didn’t know (in 2012).”

Fruit sampling remains a “really crucial” strategy in managing SWD infestation, she said.

“We also learned larvae don’t develop at typical postharvest storage temperatures for most fruits, but they don’t necessarily die,” Burrack said. “So they don’t grow anymore but they don’t necessarily go away.”

Identifying new insecticide materials to contend with SWD has been an ongoing process, Burrack acknowledged.

“With some materials we already have, it’s better if we add something that makes the fly want to eat – like sugar. Pesticide coverage is important and we need time to improve the tools we already have.

“The botton line for me remains – it’s not necessarily about killing flies, it’s about protecting your fruit with season-long management programs.”

She said trials in North Carolina and Georgia affirmed season-long approaches, as did establishing export standards and an established training program with Canada.

“In all cases, our maximum pesticide observances didn’t cross the allowable (pesticide) levels. That’s very encouraging. In all cases we had higher (SWD) mortality in our treatments than untreated plots. But when we (looked at) seven days after treatment is applied, nothing dies. Part of that was due to the rainy year in 2013.”

Early detection traps crucial

Burrack said advances in trap design, including the realization that the more holes there are in a trap enables more flies to be trapped, is a significant discovery for early season detection, as well as having holes on the side of the trap to bring more fly catches than having holes on the top of the contraption.

“A yeast and sugar mixture was much better than apple cider vinegar. It made a huge difference in what was captured.”

She presented results from 2013 trap trials in 10 different states, using six different mixtures in the traps. The traps were out for at least eight weeks.

“A fermenting cup trap and synthetic lure when suspended over apple cider vinegar caught more flies than any of the other traps,” Burrack reported. “A yeast and sugar and wine mixture caught more flies than apple cider vinegar. Apple cider vinegar was a consistent loser across the board.”

Burrack noted there were “much lower trap captures in blueberries overall than there were in blackberry and raspberries. The fermenting cup was much more attractive in blackberry and raspberry sites.”

She said there was not a significant difference in the gender of flies that were trapped, but “we caught more males in blueberry sites than females, and we caught more females in blackberries and raspberries.”

Native drosophila flies, which are not the damaging SWD variety, also make up a significant portion of the trap catches, making it important for growers to know the difference.

“The good news is that all of the newer trapping alternatives caught flies one to two weeks earlier than apple cider vinegar drops, and in some cases before fruit infestation was developing,” she said. “It’s an earlier warning than apple cider vinegar will give you.”

She said inroads are being made to identify SWD in its early stages of infestation.

“We’re showing progress in the right direction about something that might give us an earlier warning,” Burrack said. “No trap or bait combination is selective. They all show varying success. Some new lures are promising, but they can’t tell you anything more than the presence or absence of SWD in your crop.

“So when SWD are active, a management activity should be undertaken.”

– Gary Pullano