Fight spotted wing fruit fly with field sanitation, pesticides - The Packer

Fight spotted wing fruit fly with field sanitation, pesticides

11/16/2010 02:00:00 AM

By Vicky Boyd

Photo by Ed Show

Just about a year ago, the spotted wing drosophila fruit fly was confirmed in Florida.

Although the new pest didn't cause serious problems last year, that may not be the case this season, says Jim Price, a University of Florida entomologist based at the Gulf Coast Research and Education Center in Balm.

"We have a big task in front of us to work with industry and to come up with pesticides that are available or in development," says Price, who's with the university's Institute of Food and Agricultural Sciences. "Bottom line—this pest isn't leaving. We have to face it.

"We can manage it and get through this year, and it will not be devastating."

He made his comments before a packed audience at the recent Florida Ag Expo in Balm. Shortly after his presentation, he flew to Portland, Ore., to meet with other entomologists to discuss spotted wing drosophila.

Key to getting the upper hand on this pest is field sanitation, Price says.

The spotted wing drosophila, a native of Japan, was first confirmed in the United States in California in 2008.

Since then, it has been confirmed in Oregon, Utah, Washington state, Michigan, Louisiana, Kentucky, North Carolina, South Carolina, Louisiana and British Columbia.

In California, it severely damaged cherries in some cases and challenged caneberry growers. To a lesser extent, it infested strawberries.

In Oregon it also attacked stone fruit and grapes.

And there's no reason to suspect that it won't attack blueberries and strawberries, as well as stone fruit, in Florida, Price says.

He says he doubts it will attack round tomatoes. But he says it isn't known whether they'll cause problems in cherry or grape tomatoes.

Fruit fly identification

The spotted wing drosophila is a fruit fly, but it belongs to a different genus than the Mediterranean fruit fly, Caribbean fruit fly and Oriental fruit fly.

Unlike most fruit flies that favor rotting fruit on which to lay eggs, the adult spotted wing prefers fruit just reaching maturity.

The female has a serrated ovipositor that she inserts into the fruit to lay eggs, providing an entry way for fruit rot pathogens.

When the larvae hatch, they feed on the fruit flesh, rendering it unmarketable.

Japanese literature suggests the spotted wing drosophila may produce 10 to 16 generations per year in Florida.

Since it is a native of Asia, it prefers cooler climates. Based on monitoring conducted by David Dean of the Florida Department of Agriculture and Consumer Services last year, fly populations peak from December through February and remain high through May and June.

The peak populations coincide with the state's strawberry and blueberry seasons.

Identifying fruit in which eggs have been laid is difficult, Price says.

In strawberries, for example, the ovipositing site may resemble a slightly darkish spot as if a finger squeezed it slightly.

Hang traps to monitor flies

In Oregon, researchers have developed easy-to-make traps using cider vinegar as an attractant.

Price says he has found those aren't as effective if fly populations are low.

So he's developed a trap made from a 2-liter plastic soda bottle.

Drill two pencil-eraser sized holes in the bottle that allow the flies to enter.

The bait, which is poured into the bottle, is a mixture of one-half packet of baker's yeast that can be purchased at a grocery store, 12 ounces of water, 4 tablespoons of sugar and two drops of a surfactant, such as Tween.

Hang the bottle in or near host plants, and check at least weekly.

The mixture, which ferments, will attract the flies.

Keep 'em clean

At the forefront of spotted wing management will be field sanitation, or as Price describes it, managing the reproductive environment.

Instead of throwing culled fruit in the row middles, crews should put them in separate buckets or containers that are removed from the field and disposed of properly.

Conducting control measures on an area-wide basis also will be important, he says.

If you're removing rotting fruit from your fields but your neighbors aren't, theirs will attract and produce more flies that may migrate into yours.

This also is important at the end of the strawberry season when growers may stop fly treatments.

The pests could build up in those fields and move into neighboring blueberry fields.

Chemical fly control

A handful of products are registered for the pest, Price says.

GF-120, from Dow AgroScience, is a mixture of a bait attractant and spinosad.

The flies are attracted to the bait and die after eating it. The effectiveness wears off in about five days, Price says.

Another option is Nu-Lure and an adulticide.

Because the baits can spot strawberries, Price says he's working on a treatment system that does not involve applying it to strawberry plants.

John Duval, a colleague at the Gulf Coast Research and Education Center, suggested applying the material to a Styrofoam coffee cup, then inverting it on a stick in the row middles.

A handful of organophosphates also are labeled in certain crops for fruit fly control.

But Price says they have drawbacks.

Malathion, which used to be the mainstay of the Medfly program, is labeled for fruit flies. But Price says, "I haven't advised that a farmer use it more than three times in the past decade."

Lannate is labeled for blueberries but not strawberries.

Diazinon is labeled for strawberries but not blueberries and has a five-day pre-harvest interval.

They also belong to the organophosphate chemical class, an old family of products that has garnered bad press.

Danitol and Brigade are pyrethroids that are broad-spectrum. As a result, Western flower thrips may flare, he says.

"They trip the switch for bringing in a Western flower thrips problem that may be as bad as spotted wing drosophila," Price says. "I think we should hold these things for later in the season when we are not worried about changing the ecology of the field." 

For more information on spotted wing drosophila, click here.

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