Destructive pest could hit fruit growers hard

COLUMBIA–A variety of fruit fly, the spotted wing drosophila, has appeared in Missouri and made its presence felt by fruit growers.

“This is the first summer that we’ve confirmed their presence,” says Bruce Barrett, a University of Missouri Extension entomologist. “They’ve probably been here for two or three years. This has been the summer’s pest surprise in the state of Missouri.”

What sets the spotted wing drosophila apart from the 1,500 other types of fruit flies is the serrated ovipositor that females have. They can attack healthy fruit by cutting through the skin of the fruit and inserting their eggs.

“Once the ovipositor breaks through the fruit’s skin, that opens the door for fungus, bacteria and molds to enter the fruit,” Barrett says. “Also, the developing maggots will feed on the inside of the fruit.”

Barrett, who is also a professor of entomology in the MU College of Agriculture, Food and Natural Resources, says infestations of spotted wing drosophila can cause significant economic impact, especially for small growers.

“When you are a small grower who has 15 to 20 trees and the fruit in half of the trees is infested, that is definitely an economic impact,” Barrett says.

There are some challenges to combatting spotted wing drosophila. They have a very short life cycle, with up to 10 generations in a growing season.

“So it is very hard to monitor when a generation is completed because they are in various stages of development,” Barrett says. “That makes it difficult to pinpoint when to spray.”

The spotted wing drosophila attacks ripening or nearly ripe fruit, which is a big problem for stone and small fruit growers. Many insecticides have a minimum pre-harvest interval. Often a grower will need to control a problem within a few days of harvest but won’t have an insecticide that can be safely used in that window.

“Once the egg is inside the fruit you can’t spray to kill the maggot, so that fruit is gone,” Barrett says. “Once you have infested fruit, then sanitation is a big issue.”

Barrett says it’s important to remove and destroy all infested fruits. That includes all dropped fruit, where overwintering adults can live. Leaving it under the tree will mean the flies will be there the next season.

“Next year we’ll conduct more research-oriented projects that will help us provide some solutions to growers,” Barrett says. “Right now we’re just putting out fires. We’re answering questions, writing guide sheets and directing people to online resources.”

For more information about monitoring and managing spotted wing drosophila, see the Aug. 2013 issue of Missouri Environment & Garden at ipm.missouri.edu/meg/.

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