Winning war over Spotted Wing Drosophila

Oregon Ag responds to the Spotted Wing Drosophila
Commercial fruit growers managing the insect so far
Oregon Department of Ag.

So far this summer, Oregon’s fruit crops have made it to the marketplace in good shape despite fears that a tiny fruit fly would have a huge negative impact. A combination of an effective monitoring program and management tools for growers seems to be keeping the Spotted Wing Drosophila in check. But the real test is about to begin as the late season fruit crops ripen.

“I think we are at a critical juncture,” says Dan Hilburn, administrator of the Oregon Department of Agriculture’s Plant Division. “A year ago, it was fruit crops at the end of the season that were impacted by Spotted Wing Drosophila. This year, up to this point, the caneberries, blueberries, and cherries that have made it to market have been high quality and without problems. But we don’t know if that’s because of the efforts being made by growers and others, or if the insect is always going to be an end-of-the-season problem.”

The message to consumers is that local fruit they find in the marketplace is clean, good tasting, and nothing to worry about. The message to growers is to stay vigilant.

Working with the industry are four major players- ODA, Oregon State University, the US Department of Agriculture’s Agricultural Research Service (ARS), and Peerbolt Crop Management, a private consulting and insect scouting service located in Oregon. The State Legislature’s approval earlier this year of $225,000 for research, monitoring, and education reflects the seriousness of the pest.

In entomological shorthand, Spotted Wing Drosophila is known as SWD. Its formal name of Drosophila suzukii suggests a foreign species, which is exactly the case. But this is an foreign pest- an invasive species that first showed up in the Pacific Northwest late last summer and early fall. A few growers lost significant amounts of fruit last year because of the insect. What makes SWD especially troubling is that its larvae infest ripe and ripening fruits, unlike most fruit flies that only bother rotting fruit. Once the larvae hatch and begin feeding, the fruit completely disintegrates. It’s almost impossible to detect damaged fruit until it is too late. The insect is capable of producing 10 generations of pests per crop growing season. Eradication is not a viable option. Control is the best chance Oregon has in protecting crop yields and maintaining markets.

“We are getting to the point now where we will learn whether last year was a fluke and whether we have the tools to manage it throughout the season,” says Hilburn.

At the core of those tools is effective monitoring. Traps have been placed in berry fields and fruit tree orchards throughout the state to detect any growing SWD populations. If detections increase as the fruit gets ripe, growers are taking protective measures- primarily applying pesticides.

“Both conventional and organic growers have been monitoring and taking precautionary steps when needed,” says Hilburn. “There are many pesticide products available for use against SWD, including some that have been certified for organic use. These products are effective.”

That has been one of the important lessons learned since last year.

“Spotted Wing Drosophila is relatively easy to control using standard chemical control programs,” says Vaughn Walton, OSU horticultural entomologist.

Between the private consulting firm and OSU Extension, there are eight scouts setting and monitoring the traps. Crops surveyed include strawberries, raspberries, blackberries, blueberries, cherries, peaches, figs, and grapes. More than 100 Oregon fruit growers have participated in the survey.

“These growers have been involved, proactive, and responsible,” says Tom Peerbolt, who runs the consulting firm. “They have overwhelmed meetings to get the information and contacts they needed. They have cooperated in the scouting program and have kept on top of the situation. We are still in the midst of the response, so no one is claiming ‘mission accomplished’ yet. But I’m cautiously optimistic that we will make it all the way through the year with minimal commercial field losses.”

The story is a little different for small growers, U-pick fields, and home gardeners. These are sites where there have been some SWD hot spots this summer. One common denominator seems to be growing a succession of crops in one operation. Those who produce strawberries, caneberries, and cherries- for instance- appear to have a build up of SWD populations. Operations that do not clean off all the fruit from bushes and trees, or let dropping fruit lay on the ground, also seem to be at risk of higher overall insect populations, including SWD,

There is also a question about the impact wild fruit may have on harboring Spotted Wing Drosophila. Himalayan blackberries- a noxious weed in Oregon- are ripening and not necessarily under anyone’s control. It’s possible those blackberries could become a reservoir for SWD. Officials will be monitoring the situation.

The Oregon response to Spotted Wing Drosophila can only be given a mid-term grade at this point. But the marks are generally high, and those involved feel better than they did a year ago.

“Last year, I couldn’t imagine being where we are now,” says Peerbolt. “A year ago, I was visiting the affected fields, contacting entomologists at ODA, USDA, and OSU, and trying to figure out what the heck we were up against. It was pretty scary, to tell you the truth. Major crop losses were not only possible, but likely, in my view. But the work done by government, the land grant university, and the industry to build bridges, cooperate, and put a crisis management plan in place with minimal resources has been truly impressive.”

It may be September or October before the full impact of spotted wing drosophila in 2010 is assessed. It could end up being another of the many insect pests fruit growers deal with each year. The bug will be manageable, but must be given close attention in order to ensure high quality fresh fruit in the future.

For more information, contact Bruce Pokarney at (503) 986-4559.

Disclaimer: Articles featured on Oregon Report are the creation, responsibility and opinion of the authoring individual or organization which is featured at the top of every article.