Southeast growers on the watch

Spotted wing drosophila has some growers worried, researchers on alert and others beginning to learn about this invasive species of fruit fly (Drosophila suzukii).

The male spotted wing drosophila.
Photo by Gevork Arakelian, Ph.D., L.A. County Dept. of Agricultural Commissioner/Weights & Measures.

When the SWD was first discovered in California strawberry and caneberry fields in 2008 and then moved north into British Columbia, wreaking havoc in thin-skinned fruit crops along the way, it was considered a West Coast problem.

Given grower reports of losses to SWD of 10 to 80 percent of their crops, East Coast growers, particularly those in the Southeast, took notice when SWD was identified in Florida in August 2009.

University of California Cooperative Extension Strawberry and Caneberry Farm Advisor Mark Bolda is at the leading edge of West Coast grower response to SWD.

Bolda says, “We are talking about a $2.57 billion reported loss by strawberry, blueberry, raspberry, blackberry and cherry growers in California, Oregon and Washington in SWD’s first year, and this number considers only production value without any market reaction.”

Bolda uses a hypothetical average of 20 percent yield loss that increases or decreases by crop and production area. He has co-authored a comprehensive look at SWD, titled “Spotted Wing Drosophila: Potential Economic Impact of a Newly Established Pest,” that is posted on the UC Davis Web site at www.agecon.ucdavis.edu/extension/update/articles/v13n3_2.

Florida: strategies in place

The Florida Department of Agriculture and Consumer Services (FDACS) Entomology, Nematology and Plant Pathology Bureau Chief Dr. Greg Hodges says, “The SWD situation on the West Coast situation was closely monitored by the FDACS Division of Plant Industry, and we did anticipate the possibility of an SWD introduction. This allowed for us to be proactive and ahead of the game on trapping and screening of traps for potential SWD specimens. Essentially, this allowed for us to have an early detection system in place prior to the introduction of SWD into Florida.”

SWD was identified in traps located within Florida’s strawberry region in August 2009, prior to the October plantings. The assumption is that the pest arrived there by product transport.

Florida has an extensive trapping network, particularly in central and south Florida.

Hodges says, “We monitor for fruit flies year-round in every county in Florida from the Keys to Jacksonville. SWD is attracted to the multi-lure traps we use for other types of fruit flies throughout the state. We also monitor yeast and sugar water fixed bait stations for SWD. Dr. David Dean analyzes collections in his lab. His watch throughout the winter months kept our agricultural industry well-apprised of the SWD situation and kept University of Florida personnel informed about its movement. To date, we have found SWD in 20 counties in Florida, but do not consider it a pest in any crops as yet.”

University of Florida Entomologist Dr. Jim Price is a strawberry crop extension specialist and research entomologist in Hillsborough County, where SWD was first found in Florida. Price says, “We immediately contacted the strawberry growers association, attended grower meetings and provided extension educators in every county in Florida with the immediately available info and our best guess as to SWD’s possible impact here.”

FDACS Taxonomic Entomologist Dr. Gary Steck says, “Although spotted wing drosophila is here, we are not seeing the effect that California has experienced and it is not problematic yet in Florida. One reason may be that our growers already spray strawberries for the melanogaster fruit fly [Drosophila melanogaster] and that carries over to SWD.”

Hodges adds, “We had a pretty cold winter in Florida this past year, but we are not sure if that has impacted the low level of SWD in our strawberries this spring. We found a few flies in cull berries left in the field, but no damage to the crop. Next winter could be an entirely different situation.”

In early May, University of Florida Small Fruit and Vegetable Entomologist Dr. Oscar Liburd shared SWD management strategies with a group of 50 blueberry growers.

“Although the spotted wing drosophila is in a different insect family to the blueberry maggot, the behavior is very similar. The blueberry maggot is a significant pest in the Northeast and in states such as Georgia, North Carolina, New Jersey and Michigan, and the management programs that were developed for the blueberry maggot fly give us something to work from for managing spotted wing drosophila,” Liburd says.

He points out, however, that while the blueberry maggot fly has only one generation each year, SWD has the potential to produce multiple generations under Florida growing conditions. (Cooler climates may support generations in the double digits.)

Liburd suggested some growers apply exclusionary and preventative measures to suppress SWD activities. This can be achieved by adopting good cultural practices and mass perimeter trapping with smaller acreage operations.

“The use of netting and kaolin clay, a chalk-like particle spray, are two organic measures growers can use to prevent and discourage female flies from depositing eggs into the fruit. Optimal harvesting and field cleanup will reduce the breeding sites available to SWD,” Liburd says.

Georgia: will SWD impact exports?

USDA APHIS, the Georgia Department of Agriculture and the University of Georgia are trapping for SWD in Georgia. University of Georgia Extension Entomologist Dan Horton is focusing his sampling efforts for SWD in commercial blueberry and peach orchards and is encouraging growers to be observant and practice vigilance in orchard pest management.

“To our knowledge, spotted wing drosophila is not yet in Georgia, but the risk for rapid spread exists. We are particularly concerned for growers who export fruit.”

SWD leaves only tiny exterior puncture wounds. The larval damage inside can go undetected by growers and packers, leaving consumers to discover it. Some growers are concerned that shipping bans due to SWD could impact exports.

“We are encouraged by the good news that the 2010 strawberry season in Florida showed no fruit injury attributable to SWD. We would like to know a lot more about this insect’s behavior and host preferences in the Southeast,” Horton says.

He hopes that crop is not blueberries.

“Given the size of Georgia’s blueberry export market—about 25 percent of our crop—a concern quickly developed that our growers could be hurt badly if SWD affects our exports,” Horton says.

In addition to assisting with pass-through funding to support trapping for SWD, USDA APHIS has initiated research to evaluate how levels of irradiation used to assure the mortality of SWD impact shelf life and quality in blueberries and peaches.

“We are confident irradiation would control the insect. The research is needed to provide insight on how it will affect the soft fruit,” Horton says.

North and South Carolina, Virginia on watch

The Southern Regional Small Fruit Consortium has established an SWD monitoring program in backyard gardens as well as commercial vineyards and fruit orchards in South Carolina, North Carolina and Virginia.

A broad network of extension educators, crop consultants, master gardeners and volunteers are using trapping kits modeled after those used in Oregon. The traps combine one of two sweet fermenting liquid lure solutions with a sticky card.

Nineteen trapping locations are primarily focused in North and South Carolina with a few in Virginia. Blueberry, blackberry, strawberry, raspberry, peaches and wine grapes are the targeted fruits. Traps are also being placed in non-crop hosts, including wild caneberries and Prunus species.

North Carolina State University Assistant Professor of Entomology Hannah Burrack leads the monitoring effort. She says, “We have not identified the spotted wing drosophila in this area yet, but we suspect we will catch it soon.

“We have alerted growers to be on the outlook for SWD and to use materials available from California regarding the types of pesticides that have been shown effective against SWD. Some provide longer protection than others,” Burrack says. “Organic treatments include Entrust and PyGanic, but they are short-lived.”

High-production points in southeast North Carolina’s blueberry region were under close watch as harvest began in May. Trapping data from the three-state monitoring network is posted on Burrack’s blog at www.ncsmallfruitsipm.blogspot.com.

Early warning systems and strategies

Researchers advise that trapping is the best method of identifying whether or not SWD has reached your area. In California, Mark Bolda uses one package of baker’s yeast, 4 teaspoons of sugar and 12 ounces of water to create a rapidly fermenting liquid that serves as a most effective lure for SWD. A bait-toxicant combination (GF120) with a sticky card added is also effective.

SWD does not like the hot sun, so place traps in shady areas for best catch opportunity. Best management strategies, including the following suggestions, are evolving as researchers in several states study SWD:

  • Use monitoring traps for early detection so effective management programs can be implemented early in the production season.
  • Trap with baits set to draw SWD away from production areas.
  • Practice good field sanitation: remove cull fruit and fruit left in you-pick fields to reduce breeding sites and kill immature SWD. Traps are not as sweet a lure as an accumulation of rotting fruit.
  • Dispose of unmarketable fruit to prevent SWD access.
  • Use state-approved preventative spray products. A March 2010 update from Bolda notes Delegate provided three weeks of control in California fields. Florida approves the use of malathion, diazinon and pyrethrum-based products targeted at adult flies. Organic growers can use broad-spectrum PyGanic or Entrust. Multiple applications may be required with heavy infestation. Rotate treatment products to slow resistance buildup.
  • Harvest at optimum ripeness and move harvested fruit to market quickly.
  • Watch for updates from extension, e.g., a 1939 Japanese report indicated a parasitic wasp might be a natural control option; the California Department of Food & Agriculture is looking for other natural enemies of SWD.
  • Watch for news of SWD impact in various fruit crops. Grapes were added to the list of crops at risk in October 2009 when Oregon State Agricultural Entomologist Dr. Helmuth Rogg confirmed SWD in both table and wine grapes.
  • Watch for shipping and handling strategies. Literature dating from 1939 in Japan indicates SWD may have a temperature sensitivity. Bolda says, “Constant temperatures of up to 35 degrees Fahrenheit for 96 hours or more resulted in total mortality of SWD eggs and larvae in the Japanese research. This has been anecdotally confirmed in tests in 2009 in California; however, constancy of temperature is critical and that would be a challenge for fruit shippers and sellers. The point is that we cannot rely on a cool strategy to address the suppression of SWD in harvested fruit.”

More information

Researchers, growers, shippers and consumers are all interested in learning more about SWD. Oregon State University has received a $5.8 million matching funds USDA grant to study SWD. Michigan State University has established a trapping network. Growers in Pennsylvania and New York are keeping an eye out for reports identifying SWD in North Carolina crops as a trigger point for action in those states. The following Web sites have fact sheets, blog notes and pest alert warnings.

The author is a freelance writer who keeps horses and sheep on a 100-acre farm in Mannsville, N.Y.