By Tracy Turner
A relatively new but already widespread winged pest to Ohio small fruit growers can cause significant crop damage but, if spotted early, can be managed to avoid losses, according to an entomologist with the College of Food, Agricultural, and Environmental Sciences at The Ohio State University.
While spotted wing drosophila may look like a common vinegar fly, it instead has the potential to wipe out entire fruit crops because of its propensity to attack healthy ripening fruit, said Celeste Welty, an Ohio State University Extension entomologist and associate professor of entomology.
“The bad news about this pest is that is it widespread and causes significant damage,” 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.
“But once you identify it and know it is impacting your crops, it can be managed and beaten back. Early detection is a critical part of managing this pest.”
To help growers learn new management tips for spotted wing drosophila and new methods to trap and get rid of the pest, Welty, along with Jim Jasinski, an OSU Extension educator and integrated pest management specialist, will offer a webinar May 6 from 10:30 a.m. to noon.
The webinar will teach participants the basics of adult monitoring with traps, cultural controls, how to manage spotted wing drosophila with insecticides once detected, and how to determine if fruit is infested with larvae using a simple salt water test, she said.
“The salt water test to determine if the larvae are present in the fruit requires putting the fruit in a plastic zippered storage bag or 1 quart container filled with warm, salty water and waiting 15 minutes,” Welty said. “The bags or container with fruit infestation will show little larvae floating to the top of the salt water.”
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. And the pest was spotted in 37 Ohio counties in 2013, she said.
“Spotted wing drosophila was a huge problem for growers in 2013, but because more growers are learning about the pest, spotted wing drosophila was a smaller issue in 2014,” Welty said. “In 2012, the pest was still new and caught everyone by surprise.”
Thanks to training offered by OSU Extension on spotted wing drosophila, more growers were expecting it in 2014 and knew more about what to do about it, she said.
“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,” Welty said.
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.
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,” she said.
The webinar will discuss trapping options, including a homemade one that may be more difficult to use or a purchased option that is easer to manage thanks to a new lure that is specialized to attract spotted wing drosophila.
“Growers who’d prefer to avoid using pesticides can instead try growing black raspberries or June harvest strawberries, as these two crops don’t seem to as much of a problem with spotted wing drosophila,” Welty said. “There is also a pesticide available to use that is effective and is allowed in organic growing.”
Other 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 fruits 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.
The May 6 webinar will also be archived and posted on at ipm.osu.edu and at entomology.osu.edu/welty/fruit_info1/Fruit_info.html. Participants can register for the webinar at www.surveymonkey.com/s/SWDmm2015.