Small Fly, Big Trouble

Just as berry season is approaching peak deliciousness in Minnesota, we zoom in and take a look at a tiny pest that causes problems for berry growers on this episode of Smarty Plants. Berry experts Mary Rogers from the University of Minnesota and Andy Petran, owner of Twin Cities Berry Company discuss the invasive spotted wing drosophila fly and the work being done to keep our berries dazzling and delicious. 

Smarty Plants is a podcast of the Minnesota Department of Agriculture. Visit www.mda.state.mn.us/plants-insects/smarty-plants for more episodes. Look for a new episode of Smarty Plants every month.

Transcript

Jennifer Burington: 0:20

Hello, everyone. I'm Jennifer Burington, and welcome to Smarty Plants, a Minnesota Department of Agriculture podcast that keeps you informed about invasive species affecting our environment and agricultural resources. Spotted wing drosophila might be small, but it's having a big impact on berry growers and gardeners. This invasive pest targets ripening fruit, making favorites like raspberries, strawberries, and blueberries especially vulnerable. Since showing up in Minnesota, it's become a widespread challenge affecting everything from home gardens to commercial operations. In today's episode, we'll take a closer look at what spotted wing drosophila is, how to identify it, and what you can do to protect your fruit while still making the most of your harvest. Today, we're joined by two great guests, Mary Rogers and Andy Petran, who bring both research expertise and real-world experience to this topic. Thank you both for being here.

Mary Rogers: 1:18

Thanks

Andy Petran: 1:18

Thank you … glad to be here.

Jennifer Burington: 1:20

Mary Rogers is an associate professor of sustainable and organic horticultural food production systems in the Department of Horticultural Science at the University of Minnesota. Mary is a horticultural entomologist whose research focuses on integrated pest management, plant-insect interactions, and environmentally friendly strategies to manage invasive pests. Her lab has been studying spotted wing drosophila and how to manage it in Minnesota since 2015. Andy Pietran is the owner of Twin Cities Berry Company, a research and production farm in Isanti, Minnesota. Andy specializes in high-density strawberry production inside modified hoop houses. His work focuses on adapting high-tech greenhouse growing methods to support small and emerging growers who may have limited land or resources. Mary and Andy, welcome to "Smarty Plants."

Andy Petran: 2:13

Thanks for having us.

Mary Rogers: 2:13

Thanks.

Jennifer Burington: 2:14

To start us off, what is spotted wing drosophila, and why has it become such a concern for berry growers?

Mary Rogers: 2:23

Yeah. Um, s- spotted wing drosophila, we'll call it SWD um, to make it easier. It's a very small fly. Um, it's a vinegar fly in the family of Drosophila. We call them also fruit flies, and it's very, um, similar to a more familiar fly, Drosophila melanogaster, which I think a lot of people have experienced as a nuisance pest or a kitchen pest. Um, but spotted wing drosophila is a little unique in that the females have a serrated ovipositor, so that's just a fancy word for their egg-laying structure, and it's toothed or saw-like, and it allows the females to insert eggs inside ripe berries, and so they're kind of competing with us for ripe fruit. And it becomes an economic pest. And it's, um, it-- Early on in its invasion stage, it was a real concern because it, it, sort of the population was unchecked by natural enemies. We didn't understand a lot about its biology, and it just has this really rapid, um, this ability to really rapidly increase in populations very fast. And, um, so it was, it, it was kind of a five-alarm fire for fruit producers, uh, early on in the stages of invasion.

Andy Petran: 3:39

And I think, uh, morphologically, it's kind of fascinating how you can have these tiny little differences in between species, right? Like with Melanogaster, we've had this history of being able to manage them by just making sure that everything's pretty clean. Just don't let the fruit rot- Right … don't let it drop. And, and but if you have this little tiny difference, so the serrated ovipositor, it totally changes the management techniques, and it's something that growers in this area have never had to deal with before. So figuring out how to do it most effectively and the economic fallout if you don't, or if you just lest-- Ugh, if you just rest on your laurels and do it the way that you've been used to maybe your entire career, you can have these, uh, unintended consequences. So forcing us to think on our toes a little bit here. It's an interesting, scary, and, uh, morphologically int- fascinating little problem.

Mary Rogers: 4:32

Yeah. Uh, uh, also, in addition to that, um, with a lot of insect pests, we have thresholds, and with spotted wing, we don't have- Oh, yeah … there's not a, a threshold for, for larvae in fruit. It's a zero-threshold level because people don't want to eat, um, maggots in their fruit generally. So even one egg or one developing larvae can com-completely render that fruit unmarketable, and so you can't sell that fresh fruit. So processing is another, um, consideration, but you get less value for your fruit, um, that way.

Jennifer Burington: 5:07

So I know it's not anatomically correct- Mm-hmm … but I always think of it is that she's got a chainsaw on her butt. Right. And she can make it, she can make it into berries. Yeah. I know, totally wrong. That's a good way of thinking of it. No, that's exactly how I think of it. Totally wrong body parts on that fr- fruit fly. Right. But that's how I remember it, um, because, like, there, she's digging into that fruit that I would like to eat as well, and usually fruit flies, most people know them going for, like, rotting fruit. Like, if you leave your banana sit on your counter for way too long, and then you have fruit flies.

Mary Rogers: 5:37

That's right.

Jennifer Burington: 5:38

Um, she gets these ones, spotted wing drosophila or SWD, gets in way before things are even close to being- Right… Andy Petran: um, rotting.

Andy Petran: 5:47

Yeah, that, that's- Yeah … that's the biggest difference, in that normal fruit flies are sort of an effect of the rot, whereas spotted wing can cause the rot.

Jennifer Burington: 5:54

Perfect. So Mary, when was it first discovered in Minnesota, and how has its impact changed over time?

Mary Rogers: 6:03

Yeah. Um, SWD was first confirmed in Minnesota in 2012, so we've had it here for about 14 years. Um, it was first found in the US in 2008, and then it just kind of quickly established. It, basically everywhere we looked, we found it. And, um, early on, it was a newer pest people were just learning about. We didn't have natural enemies. We didn't have a lot of management tools. Um, and it was, it was pretty catastrophic overall across the country for fruit growers. And, and here it was problematic, too, because we never had an-- b- before SWD's arrival, we didn't have any major fruit pests, and so we were really in this kind of expansion, uh, stage for y- let's grow a lot of fruit. We don't-- It's easy to grow. It's easy to get certified organic, too. Um, and then spotted wing came and completely changed the scene. Um, now we're, you know, 14 years into it. We know a lot more. We've had a lot of investment in research and extension. Uh, all the growers, it's on their radar, anyone who's growing fruit currently. And I think people are a, getting a little bit more, and I'd, I'd like to hear Andy's opinion on this. I think people are getting a little more, more confident about growing fruit again, uh, 14 years into it because we have, we've, we've learned a lot.

Andy Petran: 7:17

Yeah, it's, it's due to the, the learning, and I think just the fact that it's been here and sort of the shock factor is off. And, and Mary was talking about this. I agree 100%. If you wanted to make a recommendation to a grower of what crop to grow, you could almost always just say,"Well, just do raspberries." Yeah. Right? They can grow- Right … in sandy soil. They don't have a whole lot of nutrient requirements. It's kind of farming on easy mode. There's no such thing as that. Right. But, like, on the scale of difficulty, you can get this beautiful, delicious, high-value fruit pretty quickly and make a decent amount of revenue off of it. You're, you're never going to have issues with demand. You'll always have a pretty prolific supply, and there's no huge disease or pest pressures to worry about. And with the introduction of SWD, that entire philosophy was just turned on its head. It went from an easy mode crop to maybe one of the more difficult small fruit just because- Yeah … especially raspberries, because they're so soft, it's probably, I'd say, the most preferred fruit commercially grown for SWD to hit.

Mary Rogers: 8:20

Right.

Andy Petran: 8:21

Almost to the point where I've heard farmers talk about using raspberries as a trap crop- … to protect their blueberries or to protect their strawberries. So it's, it's, it's a fascinating sort of development in that it, we had the shock factor, but now because of all the research coming out and people becoming more used to it, um, folks are pivoting back to fruit that had been commonplace in decades prior.

Jennifer Burington: 8:49

So what does spotted wing drosophila look like, and how can people tell it apart from other small fruit flies?

Mary Rogers: 8:58

Yeah. Um, it's really small.

Andy Petran: 9:01

Yes,

Mary Rogers: 9:01

they are.

Andy Petran: 9:02

They are

Jennifer Burington: 9:02

quite

Mary Rogers: 9:03

small. Um, like two to three millimeters, if you can-- if you know what that is. Um, but, uh, so the males are a little more characteristic because they, you know, they have this spot, this characteristic spot on their wings, which it gives them their name. Uh, females don't have that spot, and so it's a little harder to tell, um, females just by looking at them. Um, and sometimes you'll need mag-magnification. So if you have, uh, if you're trapping for them with y- like yellow sticky cards or lured traps, um, that drown them, you can kind of-- you can sort the males based on that spot. And then with females, if you have a little hand lens, like a 10X, uh, y-you can r- once you start to see that, that chainsaw on their butt - … you'll know-

Andy Petran: 9:46

Yes… Mary Rogers: um, that, what And so it, it takes a little bit of experience. Um, but with, with the larvae, um, they go through three, uh, larval instars or development stages, and the first instar is the earliest, and they're kinda hard to see. But by the time they get to level three, uh, you can see them with the naked eye. And so if you have mushy fruit, like a raspberry on your plant, and you pull it from the plant, first you'll have-- you'll notice there's a receptacle that's left behind, and that will be s- if it's stained red with the raspberry juice, that's kind of a tell that something's going on. And then if you s- kind of investigate, you smush the fruit in your hand and you'll see the creepy, the white maggot or the, the third instar, that's-- then you know. Then you know for sure what you have. Yeah, and I'd, I'd say just on top of that, you can really tell if you have it based on the effect of its presence rather than- Right it itself because it's so small. So if you're growing crops, you're doing good cultural practices, you're keeping everything clean, but you still notice rot starting to happen or soft fruit- Mm-hmm … starting to occur even without seeing the SWD- Yeah … you can be pretty sure that it's there. Mushy fruit. Yeah.

Jennifer Burington: 11:01

Yeah. I can definitely tell when I get to the raspberries in our yard that are just kind of growing wild on the hillside- Yeah… that I'll, pulling a couple of them off and they're fine, and then you get to one and you're like, "Eh, it still looks okay, but it, it looks okay, but it's, like, actually squishy." I'm like- Mm-hmm"That's probably one that has spotted wing." Yes."Let's throw that in the freezer."

Mary Rogers: 11:21

Yep.

Jennifer Burington: 11:22

So, um, can you, Mary, walk us through the life cycle a little bit more of the spotted wing drosophila? You've mentioned a couple, um, uh, life stages you- Mm-hmm … of the adults and then the larvae and stuff, and how quickly can populations build up?

Mary Rogers: 11:40

Yeah. This was key to, to why it became such a significant pest so fast is because it's very rapid. Um, so we, we have the egg stage, and so the females will deposit the eggs inside the fruit, and then the eggs will hatch, and they develop in- inside that fruit. So they're kind of protected y- while they're, when they're feeding inside. And then I mentioned they go through three larval instars and, and that those are just the stages through development, and then they'll go through a pupation stage. And they do this either in the fruit, or the fruit will fall from the plant, and they might do it kind of near the soil surface. And then they'll develop into an adult and then mate, and the whole cycle begins again. Um, so females can lay 300 or more eggs within their lifetime, which is significant. And then w- if conditions are right, so warm, humid conditions, like think 77 degrees, you'll get-- you can get egg to adult, uh, in, like, 10 days. Wow. So you get rapid, um, generation build-up if the conditions are right, and then they're, um, overlapping generations. And so, um, within, you know, just a few weeks, you can go from very low populations to very high populations, which makes it kind of a, a, a tough one to manage.

Andy Petran: 12:59

That's the scariest part, I think, is that combo of SWD where it has that serrated ovipositor, the butt saw- … and then also the fact that can, like Mary said, you can get nine to 10 generations- Right in one field season. Right. Nine generations. Wow. Yeah. That's crazy. So the fact that you can go from a little bit of presence, and I think that's what surprised growers right off the bat too, is that you didn't notice it at all, and over maybe a couple week period, you went from-

Mary Rogers: 13:25

Right… Andy Petran: 0% infestation to 100% The fact that it came so quickly. So that combination made it very, very economically devastating- Right … especially right off the bat, and still even today. And it's worse, um, if you have a lot of moisture in the environment. So in, in years where we're getting ample rainfall, um, yeah, it can, it c- it's a lot worse than summers where we're having extended drought periods. So some years I, I, you know, growers are like, "Yeah, this year not a problem," but we also didn't have any rain. Yeah. Um, so the years that are really good for fruit, you know, are also really good for spotted wing drosophila.

Jennifer Burington: 14:08

And obviously they're overwintering in Minnesota. There's been, they're, um-

Mary Rogers: 14:14

Yeah … their

Jennifer Burington: 14:14

populations

Mary Rogers: 14:15

come

Jennifer Burington: 14:15

out kind of right away.

Mary Rogers: 14:16

That's, that's a really good point is they do have this winter morph stage, and so they overwinter as adults, and they, they go through this sort of developmental switch, um, in the fall where, um, they don't be- they're not reproductive anymore, and they're kind of going through the stage where they're acclimating themselves to overwintering conditions. And so they'll, they can overwinter in, you know, leaf litter and kind of these protected environments and then emerge in the spring, and then they'll, they'll start their reproductive stage again. But I think, uh, there's probably a little bit of a combination between some overwintering populations here as well as new individuals kind of coming in from warmer areas.

Andy Petran: 14:58

Yeah, I think we have this combination again of it's being so difficult to manage because you have these overwintering populations in combination with populations from other areas- Yeah … coming in. So even if you do the perfect job, which is impossible, but let's say you do the, the best job you can possibly do managing SWD on your farm, it does not guarantee that it's not going to be there next year because you can't make sure everyone else does a perfect job too. Right. Or you can't make sure that the native environment around your property isn't harboring them as well. So- It has a staying power because this combination of its ability to emigrate from other areas and also to overwinter in the same area. I've seen spotted wing drosophila in my house, like, in January at times. Really? Yes, I have. I've found them. Which was not good for morale, but- Yeah… interesting from a scientific perspective.

Jennifer Burington: 15:57

So how significant are the economic impacts of spotted wing drosophila for growers and local agriculture?

Andy Petran: 16:06

Yeah, anecdotally, I'm hoping maybe Mary has some exact numbers in terms- Yes … of the economy statewide. But anecdotally, just from my own experience in talking to other growers, like I said, you can go from having a thriving operation to completely losing your crop in one field season. And if that's a reality, which it is for SWD, it can have this massive economic impact, not only in the reduction in supply for consumers, but also the viability of small farms in general. Like I said, you can have raspberry go from an easy mode crop to probably something that's not even viable if you're not taking care of the SWD on your farm. So the economic impact can be huge. It can force you to spend more money on control, to completely adapt your practices, to pivot to completely different crops. And if your infrastructure is based on one specific thing and you have to completely change that infrastructure just because of one little invasive insect, it can have these reverberating effects, not only on your own farm, but the economy of the entire state

Mary Rogers: 17:16

Yeah. Back in, um, like 2018, 2019, when we were really, um, getting hit by, um, by spotted wing and we were starting to see the impacts, we did, uh, we worked with an applied economist, um, Gigi DiGiacomo at the University of Minnesota, and she, she estimated the impact just on raspberries in our state to be 2 million in losses, and that we c- we considered a conservative estimate because it didn't get at the loss of acreage that would have been planted if spotted wing hadn't been present. So it can, it can be pretty significant. And we're not a huge fruit-producing state, but $2 million is a lot, and that doesn't also get at the impact that it had on home garden gardeners or community gardeners and the, the, um, folks growing raspberries, um, as a hobby.

Andy Petran: 18:02

And we're not a huge fruit-producing state, but we're a massive fruit-consuming- That's

Mary Rogers: 18:06

true. We love our fruit… Andy Petran: state. I think Driscoll's did an analysis and found that the Twin Cities metro consumes- We're a hot market

Andy Petran: 18:13

for fruit. Yes. We consume more raspberries and small fruit per capita than any other metropolitan area in the entire United States, so we- Which

Mary Rogers: 18:20

should drive our local production.

Andy Petran: 18:21

Exactly. Yep. Yeah. It's like the-- I've-- And I have found this since I started my farm, the demand is absolutely there. Even just for my strawberries, I have never not sold out of strawberries at a single farmers market. We have the best- We have

Mary Rogers: 18:32

huge demand.

Andy Petran: 18:33

Yes, we have huge demand, so when a fly like this comes up and potentially disrupts the supply, you have this massive economic fallout, but even a social fallout, too, because people love buying local produce- Right for the taste and also for supporting, you know, their communities, so- Mm-hmm … it's, it's, it's a Drosophila disruptor, I guess you could say.

Jennifer Burington: 18:56

Perfect. Well, and we've talked a little bit about wild host plants- Yeah. Kind of mentioned it a little. But how do wild host plants like buckthorn or elderberry play a role in spotted wing drosophila population?

Mary Rogers: 19:12

Yeah. Um, it plays a significant role, and this is also, um, one of the, the things that makes management so challenging, is we have a lot of-- So for the, for the crop hosts, we talked a lot about raspberries, blueberries, also sour cherries are a host. But then there's all of this non-crop host in the envir- host plants in the environment. And so if you're imagine having a fruit farm and you're looking at these sort of edges of the field where you have wild kind of un-unmanaged habitat, you're going to have buckthorn, you're gonna have wild honeysuckle, maybe elderberry. These are, these plants are all hosts. And so spotted wing is able to take advantage of those non-crop hosts in the environment and kind of move back and forth. Or they're there earlier, depending on the phenology of the fruit and when these, when these wild, um, non-non-crop hosts, um, are ripe, are ripe. So you'll have a population there already. And so, and it's, and it's hard to manage, right? So, um, we have-- we've, we have a, um, involved with a current project at the University of Minnesota looking at the extent that invasive honeysuckle is supporting spotted wing drosophila, and so you have an-- it's a great case of invasive supporting invasives But yeah, they act as bridges really and, and reserve or a reservoir for these populations.

Andy Petran: 20:35

The social fallout of this reality is that I can't, I'm telling you as a farmer, it can get depressing, but then it, you get to a certain point where it's almost a relief because you realize, oh, there's, I don't have to worry about wondering if it's here or when it's going to come. Like, 'cause that first step of being scared of it arriving can have like sort of mental effects on you as a grower. But once you get to past that denial phase or worry phase or anxiety s- stage, in the off-season, you can think, "Okay, I know it's coming, so now what can I do about it?" Right. Being able to get past that hurdle, I don't even worry about if it's here anymore because I know that it is. Right. And that means I can devote all of my energy into figuring out how to reduce the population, reduce the effect on my revenue, and increase the viability of the farm. Perfect.

Jennifer Burington: 21:30

Uh, for listeners who may have just a few berry plants in their yard, like myself, uh, why should they worry about this pest?

Mary Rogers: 21:38

Yeah. Um, I, I think, you know, we all, we all wanna eat our fruit, and we're not gonna eat it if it has, um, maggots in it, right? So, um, so i- it's going to reduce, you know, the overall quality and number of fruit that you get out of your home garden and your, and your plots at home. Um, so, a- and you also could be p- I think it's, I think it's worthwhile thinking about how good management and stewardship too because you don't- Mm-hmm if you're, if you're not taking care of your fruit, then you're serving as a reservoir for other folks around, and, um, you're just kind of maintaining that population. But I, I, I would say it's a little easier on a smaller scale, right? To manage it, um, frequent harvesting and then just keeping, kind of keeping your plants clean and kind of, uh, making sure that you don't have a, a lot of overripe kind of rotting fruit around. Um, some growers, um, I've heard of use or gardeners will use like landscape fabric, and then it's easy to kind of clean up any fruit that falls. Um, I know, um, a friend of mine has a sour cherry tree in her backyard, and she really loves those cherries. And so she, um, invested in like net, a net that she just put over her, her tree, uh, when the fruit was green and still hard and not ripened yet. And so, um, that way, um, she had some fruit protected from, from spotted wing. So that can definitely help. So I think, you know, s- things like frequent harvesting, sanitation, these are all really good tools. Um, Andy also did some work when he was in the lab at the University of Minnesota on, on pruning and just kind of, um, because the flies really love kind of this cool, humid, protected habitat. If you, if you prune your plants and kind of open up that canopy, that's better for plant health. It reduces diseases, and it can also re- reduce the habitat for spotted wing.

Andy Petran: 23:29

Correct. And there are these recommendations that- Researchers will observe all the time based on their meticulous observations, and some of the recommendations, they sync better with a more commercial scale. Like if you have to use a spray, there are very few home growers- Right … that are using insecticides, and I, I would agree with that 100%. But then there are some recommendations that are unfeasible at a large scale. Things like making sure that the understory of your, you know, five-acre blueberry farm is totally free of blueberries. That's not going to happen. Right. But it is something that can happen if you just have a couple plants- Mm-hmm … in your backyard. I also have just a couple raspberry plants in my backyard as well because I'm a sicko. I, I work with fruit all day, and then I come home and work with fruit. Uh, something if you are a home grower and you want to observe to help keep maybe the leaf litter down or things in a just feasible environment, not only for yourself, but for keeping SWD concentrations low, I would encourage you to observe your raspberries this year and see if the flowers are occurring on only the green canes or if they're also growing on the brown canes. And we can get into the scientific jargon about all this if we want to. But basically, if you are noticing that you are getting fruit on your green canes, you can go ahead and mow down every single cane at the end of the field season. Just mow them all down because then they're just gonna come back up the next year, and you will get fruit every single year, and you don't have to worry about this intensive pruning techniques. That's why you get these brambles, because you feel overwhelmed with, "Well, what am I gonna prune? Which brown ones do I keep? Which brown ones do I remove?" If you're getting the fruit on that green cane, just mow everything down. Remove every single cane every single year, and they're gonna pop right back up and give you more fruit, and it will help keep SWD overwintering populations a little bit lower locally.

Jennifer Burington: 25:28

Hmm. Something I'll have to look for on my raspberries this year. So what should people look for in their fruit to know if spotted wing drosophila might be present? We talked about it a little bit earlier, but now when this'll be about the time that, um, when people are out harvesting their fruits, what should they look for? Oh,

Mary Rogers: 25:51

is this for you?

Andy Petran: 25:52

This one's re- Yeah, this one's real easy. Um, if, if the fruit falls apart in your hand, that's what you should look for. If you stick your hand in and your first reaction is, "Ew, bleh," that probably means that you've got some SWD. Just the, the biggest effect is going to be sunken fruit. It's going to be, um, this degradation of the cell wall structure because the larvae are eating through as they're growing and getting larger, and also just looking for the physical presence of the flies themselves. Um, if you, if you want to think about if you're seeing something flying around you and it looks like it could be a Drosophila or it could be something else, I'd say married Drosophila are more of lazy flyers. They kinda hover more.

Mary Rogers: 26:36

Mm-hmm.

Andy Petran: 26:36

And so if you've noticed something zipping around real fast, it's probably not gonna be SWD. Yeah. Would you agree with that? And

Mary Rogers: 26:43

they, and they, um, are more present at dawn and dusk. Mm-hmm. They like this kind of, you know, th- they don't like direct heat and sun. And so you- The crepuscular. That's right. That's a great word. Like beavers. So, so, so sometimes you'll go out, I don't know if you've observed this, but if you go out really early in the morning-

Andy Petran: 27:00

Yeah… Mary Rogers: to your fruit plants- see like clouds of these little, and it's like, "Oh no, I hate to see that." But, um, yeah, that's, uh, that's another, that's another sign. Some, some folks will trap for them, and that, that, I think that happened a lot. The adult traps were something that we were recommending for monitoring early on, kind of in the invasion period. Um, but now I think we, we should-- it's safe to assume that you're just going to have them. And, um, and you, and now I think people are a lot better at, at noticing that mushy fruit or that- Mm-hmm sunken fruit and, and, and as an indication that there's, there's larvae. Yeah, I think what we've observed over time is that the traps were useful at the beginning of this invasion-

Mary Rogers: 27:40

Yeah… Andy Petran: but they're not or significantly reducing the overall local population. Yeah. So don't think that you can put some traps in and use that to solve your SWD problem.

Jennifer Burington: 27:56

And perfect. So if someone finds a larvae in their fruit, um, 'cause it's a little squishy- Mm-hmm … or even if it's not, is it still safe to eat, and what should they do with it?

Andy Petran: 28:09

So this is a really good question, and it's gonna be based on your personal preferences, personal tolerances. If you can't stand the idea of eating an infested fruit or even with just a tiny little egg in it, you know, you can, you can throw them out, and then that's your way of keeping a clean environment to reduce the probability of future fruit getting that infestation because you're removing the next generation from the environment. If you do notice it a tiny bit and you're not noticing the sunken fruit yet, if you just are noticing a couple flies and you're worried about getting to that phase where everything's falling apart in your hands, you can just pick the ripening or totally ripe fruit and just freeze it because that's-- you may get a couple eggs in there, but it's, it's totally indistinguishable. You won't be able to-- Especially if you've put it through the freeze-thaw cycle. It not only will it kill the egg or kill the larva, but it will-

Mary Rogers: 29:05

Oh, yeah… Andy Petran: if, if you have plans of the first place, then SWD isn't going to be as big of a deal for you. Let's say you're growing raspberries in the backyard because you love raspberry jam or you wanna make some strawberry syrup or something like that. You can still take fruit that has some eggs in it or maybe a first instar developing larva that it's now falling apart in your hand. You can still freeze that and totally safe. The-- There's nothing toxic about- Right … the larva. There's nothing toxic about the egg. You can absolutely still use that as an ingredient in your processed goods, and it's a good way From a home standpoint of still making use of your fruit if you get an infestation. And if you're a grower, you ca- if you do get a decent size infestation in your field, it could be an option of you, instead of selling them as fresh, just picking everything as soon as you can, freezing it, and then using it- Mm-hmm… for a processed good production if you have a, a commercial kitchen or a cottage food license or something like that. Yeah. Yeah, my recommendation to people is that if the fruit looks good, it's good. Mm-hmm. Um, at the, you know, egg and first instar stages are completely undetectable and not harmful at all. Um, if you get a little bit of softening, you know, um, y- like Andy said, processing. I also recommend just, you know, keeping those berries refrigerated and cold immediately. If you can get them into the refrigerator after harvest, that's going to make the, improve the quality and, and yeah, you won't, you won't have any further development. Yeah,

Andy Petran: 30:39

removing that field heat, it's good- Right … for the shelf life of the fruit, but then also good for reducing the- Yep … the infestation rate.

Jennifer Burington: 30:47

So Andy, what has Twin Cities Berry Company done on your farm to manage and control spotted wing drosophila? And are there particular strategies or tools that have worked well for you?

Andy Petran: 31:00

The number one most important thing that we've done, and we've done it for several reasons, this is a practice that has multiple benefits, but it also has been nice for SWD. We've pivoted all of our production inside of hoop houses, so high tunnels, caterpillar tunnels. Think of them as just slightly lower tech greenhouses. Um, we do not grow anything in the open field anymore. And I have a lot of economic, social, and environmental philosophies that align with that practice, but if we're just focusing in on SWD, one of the most important things you can do is move everything inside a controlled environment. And then for all of your entry points, all of your ventilation points, if you have side walls, you can buy this thing called insect netting. It's this really fine mesh, and if you attach it onto every single interface between the outside world and your tunnel, it will provide what's called phys- uh, just this physical barrier that helps keep the outside pests from getting in, with SWD being one of those. If you're looking to buy this for yourself, I think the mesh density is measured in like grams per meter or something like that. So if you get a 75 or 85 gram per meter mesh, and they will have that labeled on the websites where you can buy it from, it-- That is tight enough to keep SWD from getting in. I will say that Achieving 100% exclusion with this method is impossible, and that's a fool's errand. You can sink as much time as you want into rid-- to completely getting rid of this external pressure inside your controlled environment. But if you can get to like 95% exclusion, that means the ones that get in are going to be much more manageable. Maybe you can use traps to g- to control the 5% that get in. Or if you are forced into a position from a commercial standpoint where you have to use a spray, not only does the physical exclusion keep that spray frequency down, but it also completely, almost completely eliminates the risk of pesticide drift from getting outside of those tunnels. So if you only spray Pyganic or Entrust or something inside, then you don't have to worry nearly as much about a wind coming by while you're spraying and bringing it into a neighboring field or into a neighboring habitat, something like that. So physical exclusion has been our number one thing. Like I said, there will be-- I think we had one year where one of our tunnels got a pretty decent infestation anyways, and then we did have to resort to a spray in order to tamp down on that SWD. We try to-- We are not certified organic at this time, but we use as many organic practices as we can. We still use totally organic sprays Mary, from my experience, and I believe from when I was still in academia, one of the only sprays that was organically approved that worked was called Entrust. It's, uh, spinosad is the- Mm-hmm … active ingredient. It's quite effective, but it's also incredibly expensive. So- Mm-hmm that should never be for, for anything, for any pest. It's my philosophy that a spray should never be your first line of defense. It should always be your last resort. Mm-hmm. But if you do get to that point, um, putting some spinosad onto the plant is probably gonna be your best bet if you wanna keep it on the organic route.

Mary Rogers: 34:32

Have you noticed too that, um, like, besides, uh, spotted wing drosophila, that the fruit quality is just much better in your tunnels than- It's-… than in the open field environment?

Andy Petran: 34:41

So much better. And

Mary Rogers: 34:42

so you get-- It's kind of, you know- Yeah … if you're doing it, you might as well ex- try to exclude them, right?

Andy Petran: 34:47

Correct. Um, we've noticed-- I, I did a three-year trial comparing a lot of different aspects from tunnel-grown strawberries versus open field-grown strawberries, and one of the biggest differences that we noticed is the percent marketability of the fruit. Just because it's not going to be as susceptible to wild swings in temperature, you're not gonna have to worry about, uh, hail storms or just getting knocked around in the wind as much. I th- if you don't have an SWD infection, we can have around 95% marketability of our- Mm-hmm … strawberries if they're grown inside a tunnel the way that we do it, versus if you, if you have open field strawberries, especially the day neutrals that we grow that go into August, September, you can have 50% marketability or less. So there's, there's m- a multitude of benefits from growing inside a controlled environment. And, um, the economic one is huge because not only will you have higher yields, but you'll have a higher percent marketability as well.

Mary Rogers: 35:51

Mm-hmm. Andy's not gonna say this himself, but he's been really clever at figuring out how to, to use the fruit that isn't quite damaged, like with your fruit leather- Yeah at the, at the farmers market, and the syrup.

Andy Petran: 36:05

Yes.

Mary Rogers: 36:05

So good.

Andy Petran: 36:06

I'm-

Mary Rogers: 36:07

So the fruit that you're not selling fresh and ripe or that might have blemishes or imperfections or maybe minor spotting- We've- … you can process… Andy Petran: from, from a, from a personal the point where we make more money per pound of fruit from the processed good- Really?

Andy Petran: 36:22

than we do. Yes. Um, it's-

Mary Rogers: 36:23

And it's just because no one else is really doing it, right?

Andy Petran: 36:25

Yeah, it's a combination of the quality of the product, plus I think we've, we've done a decent job with marketing and with labeling. I hired a graphic designer to, uh, have really nice labeling on our products. When f- you have to understand the psychol- this is gonna be a farmers market podcast now. Sorry. You have to understand the psychology- … of the average farmers market consumer, and they want to buy something nice, and they wanna feel like they got something beautiful. So if you're just slapping a black and white sticker on a jar of jam, y- that's gonna have a much lower probability of being purchased, whether if you just put a couple hundred dollars into hiring a graphic designer to get, to just make it look pretty. That's what people want almost more than the product itself. So you can clear out your supply, you can do a little bit of a premium because people want to feel like they got something nice. And- And

Mary Rogers: 37:18

so you almost have no waste, right?

Andy Petran: 37:19

Yes. We have almost zero waste. We use every part of the buffalo. The buffalo being the strawberry. We, we have this wonderful product called a fruit shrub, which is a fruit infused drinking vinegar, and we macerate a lot of the juice out of the strawberry and then cold press it into a white wine vinegar. But then we still have, like, this, these spent strawberries.

Jennifer Burington: 37:39

Mm-hmm.

Andy Petran: 37:40

And I remembered a story I heard about craisins. Um- Ooh … Ocean Spray using the spent cranberries from making their cranberry juice and drying them, throwing a little sugar on it, and selling it. It used to be a waste product, but now they make- Mm … more money from that waste product than they do from the cranberry juice, and I thought that was super clever. So I took the spent strawberries, and I started making a puree and turning it into fruit leather. And now the fruit leather's gotten so popular that I don't have enough spent strawberries from the shrub- … to satisfy the demand. So I'll take totally ripe, fresh strawberries- Wow … and turn that into fruit leather. So we'll harvest twice a week. The early week harvest almost entirely goes towards processed goods production, and then the late week harvest goes to, um, the fresh for the weekend farmers markets. Nice.

Jennifer Burington: 38:30

Yeah, I know a lot of people do, try to do, like, the fruit leathers at home and stuff. Yes. Mm-hmm. And all the trays. The just- It's so finicky… Andy Petran: uh, it's so

Andy Petran: 38:36

nice. It's my least favorite thing to make bec- but it's, people just love it. It's the only product I make that my daughter eats.

Jennifer Burington: 38:44

Yep. It's like just the, um… I remember, like, Fruit by the Foot and like- Yes, right … all those other- Yep … other things and stuff, and it's just one. But healthier because it's- But healthier because it's actual fruit. I tell people

Andy Petran: 38:55

it's a fruit roll-up that's actually fruit.

Jennifer Burington: 38:57

Yes. Right. There you go. Perfect. Well, that's good. I'm glad you're able to use all of them. Um, so going back kind of to talk about home growers a little bit here, uh, what are some simple, effective steps that home growers can take to reduce spotted or- Mm-hmm drosophila problems?

Mary Rogers: 39:13

Yeah, yeah. I think with these processing things we were talking about, it's a good way of, of using some fruit that might be less than perfect. Yeah. But really, I… it kind of goes back to the basics of just, um, w- watching your fruit, um, picking when it's ripe as frequently as possible, especially if this is raspberries because, you know, i- i- raspberries could almost be picked daily because- Yep they'll- Mm-hmm … keep ripening. Um, so not letting that fruit stay on the plant too long, not letting it go overripe, um, clean- cleaning up excess fruit, keeping things pruned and kind of sanitized and clean. And these are all good strategies anyway for keeping your plants healthy and productive. Um, and then just those, uh, that keeping post-harvest, picking your fruit, keeping it cold is, is important.

Andy Petran: 40:00

I'd piggyback on that. The, the only other thing I would add is because the SWD has this massive generational frequency per field season, you can get nine generations per field season, and you get this population density buildup where as the field season goes on, you just get more SWD, more SWD, and more SWD. And where when we get to probably, Mary, I'd say late August to early September is, is when populations are gonna be- Right. Are the

Mary Rogers: 40:28

highest.

Andy Petran: 40:28

Yeah, are gonna be the highest. Right. So if you plan your backyard garden in a way that doesn't line up with that population density spike, then you're just gonna have less native risk of the SWD being there. So there are, there are some blueberry cultivars that will fruit a little earlier than that massive spike. Uh, if you grow June-bearing strawberries, if y- instead of the day-neutrals that we do, where you're gonna have most of your harvest at the beginning of the field season, you almost don't have to worry about SWD very much at all. We call this phenology management, where you're trying to desync the ripening and harvest period with the population density spike of the pest. So growing crops that don't line up with the time of highest population density is something that you can do when you're planning in the off-season. And then when you combine that with everything Mary said, you can probably have a pretty decent chance of reducing your infection rate even without the use of sprays.

Jennifer Burington: 41:31

Well, perfect. And then Mary, what are new research or what new research is underway- Yeah … to manage SWD more effectively?

Mary Rogers: 41:40

Right. Um, so a couple exciting things are happening. Um, I, I've been involved with, uh, you know, because this is a national pest, um, a lot of the research that we've done on this has been multi-state. And our last, uh, f- multi-state funding opportunity was really looking at biological control and trying to suppress, uh, spotted wing drosophila with, with other, um, insects. So we call this biological control, um, or b-by using natural enemies. Uh, um, and a lot of effort has, had been traditionally focused on, on this classical biocontrol model of going into the-- going into Asia and the, um, the locations where spotted wing was native and looking for what is suppressing it there, and then a lot of research and investigation and, and choosing and selecting the right agent that's a specialist that we could maybe import and release, um, uh, for fruit farms here. Um, so that, that process had been going on, but in the, in the interim, we-we've started to see this tiny, um, parasitoid wasp. So this is a wasp that's non-stinging. It doesn't have any interest in humans at all, and it's called Leptopilina japonica. And it's, it, it happens to be a drosophila generalist, so it will, it'll, it will attack spotted wing drosophila as well as other, like Drosophila melanogaster or other drosophilids that are non-target, which is not what we really want in a biocontrol ag-agent. We, we, we want things to be specific and targeted. Um, but this, uh, seems to be, um, wh-where we're looking for it. Everywhere we're looking for it, we're finding it. So we don't know how it got here, um, but it has appeared on, on, in these, particularly in these woody, unmanaged areas where there's a lot of buckthorn or wild honeysuckle or elderberry, this non-crop fruit that we were talking about. This is where we're seeing this Leptopilina japonica. And I think that since it's here, um, it's providing some suppression. And so this is kind of where we're, where we're looking. And it, and, and this is-- it's, it's- You know, not a bad strategy really because it's pesticide-free and, um, and it's, it's taking advantage of, of things that are just here naturally. Of course, if you have a heavy spray rotation program, you're probably killing it along with the flies. Mm-hmm. But it-- So we're keeping an eye on this, on this, um, Lep- Leptopilina japonica. And since we're in this, you know, fourteen years, we, we've seen this with other invasives too, is that there's a little bit of, you know, nature finds a way. We, um, there's things that take advantage of, of resources when they're overabundant and, and things start to kind of balance out again. So although they're non-natives, um, this, this could be, could be something interesting. But of course, I think looking at potential non-targets of, you know, other, other drosophilids and the food web kind of ecological consequences of that would be, will be important. Another thing, um, we're doing is there's been a lot of development on this sterile male technology, and this is, um, through some biotechnology, um, creating populations of males in the lab, um, that will, will mate with females but they don't result in, um, offspring. So, so if you, if you get, uh, enough of these males released on farms, they will, um, you, you can crash the population if they outcompete the wild males. Um, so this is really interesting. It's another completely, um, non-pesticidal, uh, method of control. It also would work really well with the biocontrol because you're targeting two different life stages here, the reproductive, reproduction, so you won't get the egg. But also, um, when you do have eggs and larvae, if you have this parasitoid, it's attacking that stage. So these are two things that, um, I think are, are, are kind of exciting and, and I know growers are interested in the sterile male release. Of course, this, this technique is, is really gonna be more applicable for commercial farms, larger farms than, you know, it's not really something a home gardener would use. Um, but, um, it's-- And it's still sort of-- It's in its, I, I guess, its later stages of research and development, so we're expecting to see some commercial products of these sterile males available pretty soon. So those are kind of the two things we're, new things we're sort of keeping our tabs on and looking at.

Andy Petran: 45:53

Mary, do you know, are the researchers doing anything to make these sterile males more alluring to the females than the ones who-

Mary Rogers: 46:01

Yeah, so- -did

Andy Petran: 46:01

not receive the vasectomy? They

Mary Rogers: 46:02

would have to-- Behaviorally, they would have to really be competitive with the- Yeah … with the, with the males that are already in the, in the environment. And so that we're, what we're seeing is that they, they look, they act, they um, just like, uh, you know, a, a drosophilid raised in the wild. Um, that's, that's the other thing is, you know, they're lab-reared and so you need them to be hardy and competitive- Mm-hmm… but in order for it to be worthwhile. But yeah.

Jennifer Burington: 46:27

Great. Well, perfect. And then to kind of give people, um, to give our listeners a little bit more information on management resources, do you have any locations that they can get that information?

Mary Rogers: 46:40

There's a ton of good resources on University of Minnesota Extension pages. Um, I would also plug the, um, fruit and vegetable newsletter, and this is-- they'll have timely updates on spotted wing drosophila as well as other tips, um, for fruit and veg growers. Um, I think the, the MDA also has some good resources on invasive pests, so this is, so this is part of, um, spotted wing drosophila re-resources are definitely on the MDA pages as well.

Andy Petran: 47:06

I think 'cause we're 14 years in now,

Mary Rogers: 47:09

there's- There's a lot. Yep. There's a lot of… Yeah.

Andy Petran: 47:12

Now we have bulletin boards, we have social media posts, we have podcasts now.

Mary Rogers: 47:17

Growers have- There's- Yeah, like, you know, they, they sometimes they will have the most innovative, creative ideas. Um, so I, I think, uh, yeah.

Andy Petran: 47:26

Just going to conferences and-

Mary Rogers: 47:27

Talking with other fruit growers. Yeah,

Andy Petran: 47:28

talking with other-

Mary Rogers: 47:29

Mm-hmm… Andy Petran: fruit growers is

Jennifer Burington: 47:32

Yep. There's a couple throughout the year. We have the fruit and vegetable-

Mary Rogers: 47:35

Yeah… Jennifer Burington: uh, growers and things like that- Right … that all talk about a lot of these. So if you are interested in getting, uh, if people are interested in getting involved and, um, possibly doing some more fruit production on their, um, in their backyard or even on a small farm, um, there are, uh, these education opportunities, um, especially in the fall and the winter, um, when everybody's not out in the field growing things- Right and taking care of their plants and picking berries, um, to do all these education opportunities and stuff so t-we do have a couple of those listed on our website, on the Department of Agriculture website also, um, and we try to send out information, um, to register for them as well. Well, thank you both. Uh, this has been a really great conversation, and I learned a lot, and I'm sure our listeners did too. This has been "Smarty Plants," a podcast from the Minnesota Department of Agriculture. Our producers are Brittany Revell and Sadie Anderson. Our editor is Larry Schumacher, and I have been your host. You can learn more about invasive species and plant pests at www.mda.state.mn.us. And while you're checking that out, we'll be working on the next episode of "Smarty Plants." See you there.