AUBURN UNIVERSITY, Ala.—Summer is a great time for growing and harvesting fruit. The farmers markets are filled with beautiful fruits and vegetables. However, summer can bring about many diseases and pest problems, making it difficult for farmers to produce a good crop.
Chip East, an Alabama Extension commercial horticulture agent, reveals one pest that is causing a problem in fruit around the state and country.
Spotted Wing Drosophila
Spotted wing drosophila is a type of fruit fly that causes problems in late summer. It has been in other states for several years, but was first found in Alabama in 2011. Most fruit flies lay eggs in over-ripe fruit, and that does not affect fruit production. However, the spotted wing drosophila lays eggs in ripening and ripe fruit, as well as fruits with thin skin such as strawberry, blackberry and blueberry. Thick-skinned fruits are especially susceptible.
Regional extension agents have put out traps and caught thousands of these insects in large plantings, as well as small home plantings.
“Of course all of the spotted wing drosophilas we catch are not females, but there are a lot of eggs being laid in fruit,” East said.
The insect has a complete life cycle, which means it develops from an egg, to a larva, to a pupa, then to an adult. Egg and larval stages are found in the fruit when it is ripe.
“I have found the pupal stage in blueberries, but it was in very over-ripe fruit, well past the time when it normally would have been eaten,” East said. “The insect does not hurt anyone who eats it, but it is there and it lowers the fruit quality.”
The larvae are tiny, but can be seen without a hand lens. Fruit can be checked for larvae by mashing fruit in a container and adding salt water. The small larvae will float to the top, and the berries will stay at the bottom of the container.
After harvest, freezing berries will kill any of the immature, insect stages inside the fruit. Temperatures of 34oF for 72 hours should kill any eggs and larvae. Refrigerating fruit will stop the development of the insect.
If you choose to spray, a weekly insecticide (organic options are available) application beginning just before the fruit starts to ripen through the end of the berry-picking season will manage the pest. Make sure to follow the pre-harvest recommendations on the label. If the label recommends one day from application to harvest, make sure to wait a complete 24 hours between spraying and picking fruit.
For more information about spotted wing drosophila, please contact your county Extension office.