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Farmers, Scientists Work To Find Organic Solution To Invasive Fly

Michigan State University graduate student Heather Leach takes one of the spotted wing drosophila yeast traps off of a raspberry bush
Rebecca Thiele, WMUK

Prices for organic produce are always a little higher. But lately you might have noticed you’re paying even more for berries. That’s partially because of a tiny fly called spotted wing drosophila. It’s a lot like an ordinary fruit fly, only it can lay its eggs inside a piece of fruit even before it starts to go bad.

MSU set up different high tunnels on this Coloma farm to see if they would help quell the spotted wing drosophila flies
Credit Rebecca Thiele, WMUK
MSU set up different high tunnels on this Coloma farm to see if they would help quell the spotted wing drosophila flies

While conventional farmers have been using multiple pesticides to fight the bug, organic farmers don’t have as many options. So organic farmers and academics in Michigan are coming together to find solutions.

Heather Leach walks along a row of 14-foot tall white tunnels that cover raspberry bushes at a farm in Coloma. She’s the graduate student assigned to this farm and two others as part of Michigan State University’s research program on spotted wing drosophila.

These tunnels or “high tunnels” look like greenhouses but have one or more sides open to the air.

“We’re not totally sure yet, but we think that high tunnels deter them because they can’t find the crop as well. You know if they’re flying and they see this big plastic structure they’re not seeing raspberries. Unfortunately the main cue that they use is odor, so they’re still cueing in on the fact that there’s raspberries here. So what we’ve done this year is put netting over two of these tunnels to see if we can get SWD completely out of those tunnels.”

Leach says many Michigan farmers are reluctant to tell anyone that they’re fields have SWD. Farming is their livelihood and no one wants to buy from a grower that might have maggots in their fruit. But Leach says right now it’s not a question of if a berry farm has drosophila, but how much.

"Spotted wing drosophila is everywhere in Michigan," she says.

Matt Grieshop heads the Organic Agriculture Research Station at MSU and helped start the SWD task force. Since last year, researchers and organic farmers across the country have been testing out new ways to squash the spotted wing drosophila through a USDA planning grant. For certified organic growers, controlling SWD is especially difficult. There is one expensive organic pesticide called Entrust, but Grieshop says that’s not enough.

“If you’ve got a huge population of flies out there and they’re reproducing a lot. You’re having a lot of genetic recombination through mating. And overtime if you put out something like a strong insecticide, only the flies that are least susceptible to that insecticide will survive. And pretty soon what you’ll end up with is a resistant population,” he says. 

But the research team is not just looking at insecticides. In fact, Grieshop says for organic growers that’s kind of a last resort. They’ve also tried putting netting over the plants. A lot like what you’ll find on a screen door.

“That seems to be pretty promising. The problem of course with netting is that you are looking at $15,000 to $20,000 an acre investment…to net an acre of berries,”  says Grieshop.

Grieshop says that number doesn't include things like labor costs.

Then there’s the pouch. MSU developed this. It’s just a nylon pouch filled with an insect lure, with a pesticide on the outside.

“You’re bringing the insect to the insecticide rather than broadcasting insecticide and hoping the insect will land on a treated piece of foliage,” Grieshop explains.

But MSU still doesn’t know if it will work for SWD.

Grieshop says one of the biggest hurdles is trying to out how the fly finds the fruit in the first place. After all, if they can’t find it, they can’t eat it. Last fall, researchers and farmers met in Atlanta to discuss what they found out working with the traps, and they came up with some very confusing results.

“One year we might have a commercial lure that works really really well in blueberries and the next year it doesn’t work very well. Or it worked really well in blueberries, or it didn’t work in raspberries. Or it worked really well in raspberries on the west coast, but in Michigan it completely failed,” Grieshop says.

But even when a method fails, Grieshop says having farmers in the group has been invaluable—because they know what works. Scientists? Sometimes not so much.

“We did some research and if you bury your blueberry plants you can kill this insect. Ok that’s great, but if I’m a grower—if I bury my plants—I’m going to have to un-bury them, right? So that they can get sun and whatnot. And again that’s kind of a ridiculous straw-man example, but it’s surprisingly…I suppose it’s not very surprising. When left to our own devices, agricultural scientists can come up with solutions that yes they work, but they’re not practical.”

The Organic Management of Spotted Wing Drosophila group is seeking a $2 million grant from the USDA to better combat the problem. Grieshop says they’re very optimistic.

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