Stress of the flies | Pests | Invasive species | Michigan Farm News

Stress of the flies

Category: People, Fruits & Vegetables

by Paul W. Jackson

cherry closeup mfn 2017
A luminescent sight of tart cherries is welcome, but an invader has broken the peace. Spotted wing drosophila can destroy a crop in a hurry, but researchers say it will be conquered.

Stress is wearing on Nikki Rothwell.

As she takes a phone call amid the activity buzzing around her, foremost in her mind are cherry growers who surround MSU’s Northwest Michigan Horticulture Research Center near Traverse City. She admits more than once that she’s scared for them.

“I’m a little more optimistic today than I was last week,” she said about the trap count numbers she checks daily for spotted wing drosophila (SWD) in her role as MSU fruit educator and coordinator at the Center. “I suspect those numbers will go up tremendously,” she said in early August. “It’s a real challenge for growers to get the fruit off before the SWD numbers get too high. The faster they get it off, the less likely they are to get an infestation. But there are so many things they have no control over. Maybe the processor can’t take it all that fast. Maybe the shaker breaks down.” There are more things to list, but she sighs, emotion exhausting through the phone.

When stuff beyond a farmer’s control happens – and even if it doesn’t – these nasty little invasive flies seem to thrive when stressed. Eventually – hopefully – the stress they cause will lead to their ultimate demise. But for now, the battle rages on many fronts.

There’s always some fruit left on the trees after shaking, but if we spray the (already harvested) trees, all that will happen is SWD will develop resistance,” said Francis Otto, orchard manager with Cherry Bay Orchards near Suttons Bay. “We used to have problems with cherry fruit flies, so we’d spray them and control them. But SWD has so many more generations that the pressure builds up fast. I hope they can find natural predators and get them back here, because until we get natural predation, it will be a major scourge.”

closeup fly mfn 2017
A magnified view of the SWD fly.

Part of the scourge of SWD is its ability to reproduce. The fruit fly begat one generation per year. SWD can produce 12.

“They can hatch a new generation every seven days when it’s warm,” said Phil Korson II, Executive Director of the Cherry Marketing Institute. “Each adult female can lay up to 300 eggs.”

Add to that stress a limited number of EPA-approved effective crop protection materials, a lack of natural predators, plus the fact that one maggot can cause an entire load to be rejected for market, and it’s easy to understand why the soft-skinned fruit industry has called for an “all hands on deck” approach to the stress.


There is promise for some stress relief, however.

“I think we are making progress,” said Rufus Isaacs, an entomologist with MSU who’s one of the hands on deck. “Eradication is not a likely goal, but I’m optimistic that we can control it,” he said. “When I first started at MSU, Japanese beetles were a problem, but now I don’t get calls about it from blueberry growers. It takes time. Eventually, natural enemies and other parasites catch up, but funding is essential.”

Fortunately, all the hands on deck have worked diligently to secure grants dedicated to researching control measures.

The Foundation for Food and Agriculture Research (FFAR, a farm bill project), through a program called Rapid Outcomes from Agricultural Research (ROAR), has provided funds that were matched by several stakeholder partners, Korson said.

“MSU, the Michigan Cherry Committee, Cherry Marketing Institute and the Michigan State Horticulture Society matched those funds, so now we have a total of $300,000 for research and mitigation this year,” he said. “The department of agriculture has shown its willingness to work with us, too, and I don’t think we could organize a better set of researchers than we have at MSU.”

With that funding, the result of the team effort, research has been able to expand, Rothwell said.

“Without the ROAR grant, we would not have been able to put all those boots on the ground,” she said.

Hand-in-hand with that whole-team effort for grants has come a Section 18 waiver from the EPA, Korson said.

“It was a classic partnership,” he said. “It was a great example of how we used all the talents of the people involved for the greater good of farmers.”

Thanks to efforts by the Michigan Department of Agriculture and Rural Development (MDARD), the Cherry Marketing Institute and the entire MSU entomology team to get the waiver for a pyrethroid (Mustang Maxx) in tart cherries and blueberries, there is some control ongoing.

The Section 18 waiver bumped the pyrethroid from a 14-day pre-harvest interval (PHI) to a three-day PHI. However, it can’t be used in sweets, and it’s a temporary solution, Isaacs said.

“With invasive pests like this, we need the chemicals for rapid, immediate response to control them in the short term,” he said.

The chemical of choice, Imidan, a broad-spectrum pesticide, can only be used on tarts cherries, he said. It carries a seven-day PHI, and growers are seeking another waiver to make its PHI shorter.

Also, Rothwell said, some chemicals that have proven effective have such a long PHI (the amount of time required between spraying and harvest for maximum safety) that spraying tasks – and grower costs ‑ have increased dramatically.

“I hate to tell them this,” Rothwell said the day after a 1.5 to 3-inch rain went through the Traverse City area (Aug. 3), “but they’re going to have to spray again. It’s a race to the end (of harvest) right now, and after that rain, there are no residues left from any of the 3-day interval materials. It’s not what farmers want to hear, but we’ve made it this far, and we need to finish the harvest.”

What’s next?

All parties involved will meet again in November, Korson said, to evaluate what worked this year and what did not. At that point, and even before, more Section 18 waivers will be sought to shorten other effective pesticide PHIs so SWD can finally be controlled without so much stress on growers, workers and finances.

Ultimately, though, long-term solutions mean all available crop protection products will be on deck, including new biologicals that are currently under quarantine until they can be deemed safe.

“We hope to have two of the three natural predators available for next year, or even yet this year,” Korson said. “But we have to be careful, because you’re releasing another insect, and we don’t need that to become a problem.”

There are enough problems to deal with.

“This little pest can find any hole in the spray program,” said Kevin Robson, horticulture specialist with Michigan Farm Bureau. “If the sprayer lifts up a little too soon at the end of the row, they’ll take advantage. Any little branch that the sprays missed will give them an opening. But we’re using our all-hands-on-deck approach pretty well right now, and I can’t say enough about the efforts of everyone involved. This has been an amazing team effort, and while farmers are feeling the stress right now of having to spray so much and spend so much more money, we’ll swat this fly.”

Rothwell believes that too, but as harvest winds down under extreme SWD stress, she’s too deeply involved with cherry growers to take a 10,000-foot view right now.

“I’ve seen growers, particularly ones who were a one-man show, pull trees out,” she said. “Maybe they didn’t own a harvester, and they can’t wait for it because of the pressure of SWD. And they can’t just walk away or the pest will put even more pressure on their neighbors,” she said. “I’m scared for them. In the long run, I think we will conquer it, but not with straight chemical control. It will require cultural things, biologicals and maybe even some tents over the trees. We will see some changes in the industry. Some folks may need to downsize, because it just doesn’t make economic sense to spray four or five more times than they used to.”

Eventually, Robson said, there will be some stress relief, and not the relief that comes with going out of business.

“I know it’s easy to say and hard to do, but growers need to hang in there,” he said. “They’re fortunate to have such a good team and such a coordinated effort. And they’re fortunate to have people like Nikki and this amazing team, all of whom empathize with them. There’s enough stress to go around, and the ultimate end game is to stress these little flies out of existence.”

That goal – eradication – may not be possible, Rothwell said. Control is possible. The greater, and more immediate problem, though, is the swarming stress of bringing in a crop.

“It doesn’t take much to get you down,” she said, her heart for growers showing on her sleeve. “People need someone to talk to who understand what they’re going through. They can’t talk to people who don’t understand agriculture. Our team can empathize. I just hope that helps.”