No rosy picture

Spotted wing drosophila was first detected in Washington State more than 15 years ago, but cherry growers still have limited control options. By Anna Mouton.

Tim Pitz manages approximately 800 hectares of pome and stone fruit for Mount Adams Orchards Corporation, a Washington State-based company that packs and ships pome fruit and cherries for itself and more than 55 other growers.

Mount Adams currently has about 60 hectares of cherries — a favourite target of spotted wing drosophila. Pitz spoke with Fresh Quarterly about the impact and control of this pest.

Q. How does spotted wing drosophila impact your operation?

A. It completely dictates our spray programmes and intervals. We have to spray basically every seven to 10 days once the fruit is susceptible to keep it covered.

SWD [spotted wing drosophila] isn’t technically a quarantine pest, and it doesn’t affect where we can send the fruit, but we could get rejections because of decay if we don’t keep our fruit clean. We have good optical sorting that sorts out affected fruit. The only challenge is the newly oviposited fruit that the cameras may not see.

We still get some damage, but SWD doesn’t significantly affect our pack-out. But the spray programme is very costly, and SWD pretty much destroyed IPM [integrated pest management] for cherries. I would say it was the worst thing ever.

Cherries were basically organic until SWD showed up. We had great programmes — GF-120 [spinosad bait concentrate] to control cherry fruit fly [Rhagoletis indifferens] — but SWD completely changed the game.

Q. Has spotted wing drosophila affected your planting decisions?

A. No. Even with the expensive spray programmes, we still make a lot of money on cherries in a good year. And as a packer, our company needs to pack fruit. We’re actually expanding and planting another 100 acres [40 hectares] of cherries in the next few years.

We do pretty well revenue-wise up here. We grow good quality, and because we’re a later district, we don’t hit the big peak market season. So, even though it’s a dirty, nasty spray programme, it’s still cost-effective.

Q. What are the control options for spotted wing drosophila?

A. Lambda-cy [lambda-cyhalothrin] is kind of the big hammer that we use. We also use some spinosads [spinosad and spinetoram] and a little bit of [fenpropathrin], acetamiprid, carbaryl, and a few pyrethroids.

There are not a lot of options. That’s concerning. I think we’re probably driving resistance because we’ve got about three or four products that we use consistently throughout the season and year after year. I think there already is some resistance to spinosads.

It’s concerning to me that, as an industry, our programme is still just to spray and kill them away. We haven’t come up with a more IPM-friendly solution like we did with GF-120 and cherry fruit fly. I’d love it if we could create an attract-and-kill product.

There’s also no real trapping [monitoring] that is significant enough for me to adjust my spray programme. I’ve tried. We put up some traps and worked with extension folks, but the information is never solid enough. We don’t have any good threshold data for trap counts, so we’re always hedging our bets and trying to cover and be covered.

Q. Have you observed seasonal and climatic effects on pest pressure?

A. We tend to deal with various SWD pressures every year. We can follow a pretty standard spray programme, and then, in some years, the development is so fast that they’re cranking out generations faster than our sprays can cover them. We’ve had years where we get worms [larvae] on a 10-day rotation and go back to a 7-day rotation.

Our challenges with SWD are typically in years with snow cover. The bugs live in the soil under the snow, and it’s nice and warm there. Unless we get super subzero for weeks to the point where the soil freezes, the bugs come out happier than heck because they’ve stayed in diapause nicely all winter under the snow and wake up energised.

We don’t get very hot, but Washington State does get 100–110 °F [38–43 °C] in the summertime, and SWD is throughout the state.

Q. What do you see as the future of this pest in Washington State?

A. We have all kinds of wild berries that SWD lives in. They don’t just like agricultural crops. They’re going to be happy with a lot of your native small berries and fruits. So, I would say to your guys that once it shows up, it doesn’t go away. It just expands, and it finds all kinds of hosts.

My only hope is maybe some of the sterile breeding programmes, but I think that’s just getting started.

Q. Do you have any other advice for South African growers?

A. If you don’t want damage, you have to understand the pest’s phenology. At the right temperatures, they can go from an oviposited egg to an adult that can lay eggs in less than a week, so it can be challenging, especially at high temperatures.

And they can come out pretty early. They can infect fruit that sometimes you wouldn’t think they could infect. The cuticle only has to get slightly soft, and they can shove right into it. And then you have to worry about them almost up till the day of harvest.

There’s nothing you can put on the fruit to kill the worms once they’re in it. If there are too many, you could lose the whole block.

Be aware that whatever you’re growing next to your cherries is going to struggle IPM-wise. Anything we grow next to cherries always has more pest pressure because the chemicals we use in the cherries kill beneficial insects. We see that all the time in the pear blocks.

I can’t paint a rosy picture of other controls. You must keep a tight spray interval and make sure your products have good efficacy on the pest.