Spotted Wing Drosophila Impacts Berry Crops

COLUMBUS, Ohio – John Albert is keeping an eye out for a new winged pest in Ohio that, while it looks like a common vinegar fly, instead has the potential to wipe out entire fruit crops because of its propensity to attack healthy ripening fruit.

Although the spotted wing drosophila hasn’t reached his 50-acre Ruffwing Farms produce and livestock farm in Lancaster, Albert is ready to tackle the harmful insect should it come seeking his blueberries and black and red raspberries.

“It would be devastating to my crops,” he said. “For example, black raspberries have a very short harvest, maybe a two-week window to harvest.

“So if I had spotted wing drosophila on my farm, I would have to shut down the harvest for a week, potentially resulting in a 30- to 50-percent loss while I manage the pest. It’s not a problem for me yet, but it’s important to learn how to prevent it, mediate it and manage it.”

Albert was among 27 growers who attended a training session April 30 taught by experts from Ohio State University’s College of Food, Agricultural, and Environmental Sciences on how to identify and manage spotted wing drosophila. 

The workshop was designed to provide growers and crop consultants detailed information on spotted wing drosophila, including how to differentiate it from common fruit flies and how to manage the pest while saving fruit crops, said Celeste Welty, an Ohio State University Extension entomologist and associate professor of entomology who co-presented the workshop.

“Early detection is a critical part of managing this pest,” said Welty, who also has an appointment with the Ohio Agricultural Research and Development Center.

OSU Extension and OARDC are the outreach and research arms, respectively, of the college.

“This was a big deal for many growers last year,” she said. “It can devastate an entire season’s harvest if you don’t realize that you have it and then don’t do anything about it.

“Once you find spotted wing drosophila, it takes rigorous insecticide use to manage it, including spraying weekly using a pesticide that can be applied close to harvest.”

Some growers who do not want to spray are abandoning the production of berry crops until a biological control tactic can be developed, Welty said.

Spotted wing drosophila is a fly that targets fruit crops, including cherries, raspberries, blackberries, blueberries, grapes, peaches and plums, and sometimes strawberries, pears, apples and cherry tomatoes. The pest causes damage through larval feeding on ripening fruit. Damage starts as a tiny scar on the skin of the fruit, with the skin collapsing in two or three days and mold developing.

The pest is known to cause significant losses for fruit growers in several states, including Michigan, where many blueberry, bramble and strawberry growers reported up to 50 percent fruit loss in 2012, according to a report from Michigan State University Extension.

In Ohio, spotted wing drosophila was detected in Champaign, Clinton, Warren, Montgomery, Guernsey, Holmes, Wayne, Medina, Wood, Fulton, Fairfield and Meigs counties in 2012, Welty said.

The pest was spotted in 37 Ohio counties last year, she said.

The adult male spotted wing drosophila is distinguished from other fruit flies by spots on its wings that are visible with the naked eye and two dark bands on its front legs that can be viewed with a 40x magnifier. The adult female spotted wing drosophila is distinguished from other fruit flies because of its saw-like, hard ovipositor, which also can be viewed with a 40x magnifier, Welty said.

Growers can determine if spotted wing drosophila is in their crops by setting up traps to monitor any activity.

Growers can follow these steps to make their own traps:

• Get a clear plastic jar or cup with a lid.
• Add the color red --by adding a strip of red duct tape, for example -- as it attracts the fly.
• Punch holes near the top of the jar or cup along one side.
• For a simple bait, use apple cider vinegar, 1 inch deep in the plastic cup, and add a drop of dish soap.
• For an improved trap, add a small cup of fermenting bait made from yeast, sugar, flour and water, with a fine-mesh top; place this inside the trap so it floats on the vinegar.
• Use a strainer or paint brush to remove trapped insects.
• Change the bait weekly but do not dump it in the field.
• The threshold level is the capture of a single confirmed spotted wing drosophila adult.
• Beware, many non-target insects are likely to be caught.

Management tips include:

• Do not delay harvesting: Pick as soon as fruit ripen.
• Keep harvested fruit cooled as soon as picked.
• Sanitation is critical. Collect and destroy unharvested or damaged fruit every two days. Put culls in a clear plastic bag and leave it in the sun for one week, or bury it 2 feet deep.
• Netting is a mechanical control option, especially for organic growers.
• If any spotted wing drosophila are found in the trap, then the fruit crop needs protection by insecticide, starting when fruit begin to ripen or berries start to turn color, until the final harvest.
• Spray every seven days with insecticides that provide seven days residual activity.
• Do a salt test weekly to see if the control program is working well: Put a sample of fruit in a bag with warm salty water and wait 15 minutes to see if any larvae are present.

Jim Jasinski, an OSU Extension educator and integrated pest management specialist who co-presented the workshop, said identification of spotted wing drosophila is key to combating the pest.

“The most important thing for most growers is to identify spotted wing drosophila, monitor it and then manage it,” Jasinski said. “Once you find out that you indeed have spotted wing drosophila, then you can begin weekly spraying.”