TRANSCRIPT Running on Fumes: Strawberry’s Dirty Secret

This is a transcript of the Gastropod episode Running on Fumes: Strawberry’s Dirty Secret, first released on August 27, 2019. It is provided as a courtesy and may contain errors.

MATT CELONA: In the first year that we did pick-your-own, we tried to do it on two days, Saturday and Sunday. And so we put a barrier like thinking like, okay, people will pick this part of the bed today. And the people literally pushed the barrier over and picked the whole thing. It was crazy trying to control the crowds. And it’s like, for those few hours it’s mayhem and we call it, like, strawberry zombie time.

CYNTHIA GRABER: This is basically me in June at the farmers market. I can’t buy enough—I bring home quarts and quarts and I eat as many as I can and I make ice cream and popsicles and then I freeze whatever I haven’t devoured. I am a strawberry zombie.

NICOLA TWILLEY: This has never happened to me. Because, to be honest, I’m more of a raspberry girl. But Cynthia, I hate to break it to you—we can get strawberries basically all year round in the great state of California.

GRABER: Not just you—everyone can get California strawberries all year round. That’s where nearly all the strawberries for the entire U.S. are grown today. I have to say, I don’t love those year-round strawberries, I think they’re basically flavorless. I reserve my enthusiasm for the local ones in the summer. But this does make me wonder: How did California corner the market on strawberries?

TWILLEY: That’s the story we’re telling this episode: it’s that age-old tale of an innocent young berry that heads west to California to make its fame and fortune and loses its soul in the process. Cue violins.

GRABER: That soul it lost, it’s not just the missing flavor. It’s also the deal with the devil the strawberry had to make to become so world-famous—that is, its deep entanglement with chemicals known as soil fumigants.

TWILLEY: So what are fumigants, and how did strawberries end up in bed with them?

GRABER: Plus, what’s their impact on the environment and on human health? And can the two ever get a divorce?

TWILLEY: All that plus a sneak peek at the strawberries of the future. But first we have a couple of important news flashes. In case you’ve been living under a rock: we are having a very important birthday. That’s right, Gastropod is turning FIVE! In September!

GRABER: Five whole years! Which is actually an eternity in the podcast world. Sometimes it seems that way to us, anyway. But we are celebrating!

TWILLEY: And you are invited—we are making a special birthday episode. Also, if you happen to want to get us a birthday gift, hint hint, now is the moment to do it! We’ve got a super special prize for anyone who donates between now and the end of our birthday month—just go to

GRABER: We’ll be offering this special birthday present for all of you, and, of course, for us, until the end of September. And if you’re a long-time Gastropod supporter already, don’t worry, we haven’t forgotten about you! We have a special present for you, too, in honor of our birthday. We love feeling the love from all of you, and we are going to give it right back!


PATRICK EDGER: So that’s actually a common misconception is that what we call the fruit is actually not the fruit. It’s a botanical organ called the receptacle. And if you ever look on the strawberry fruit itself, the little—you’ll see little studs of what we sometimes call seeds. Well, those are actually individual fruits. And the seeds are within those.

TWILLEY: This is Patrick Edger. He’s an assistant professor at Michigan State University and he studies plant genomics. He’s been on Gastropod before—he described the evolutionary war between butterflies and cabbages that gave us mustard.

GRABER: And in case Patrick’s botanical description of the strawberry caught you by surprise—and we were surprised, too—yes, he really is saying that the delicious red berry you eat? It’s not fruit. It’s the receptacle for the fruit. Basically, it’s the fleshy growth from a flower that forms to hold all the fruits.

TWILLEY: And the things you think are seeds on your delicious red receptacle? Nope, those little sesame-seed-looking dots, those are the fruits! The real seeds are hidden away inside them. I feel like my entire relationship with strawberries is built on a lie.

GRABER: Fruit or not, my zombie relationship to strawberries is mostly because those fleshy receptacles entice me with their smell.

TWILLEY: You are not the only one to have noticed this.

EDGER: So strawberry or its Latin name Fragaria was named by Linnaeus because it has a sort of striking aroma to its fruit.

GRABER: The ancient Roman poet Virgil called the strawberry ‘fragrant fruit born of the soil.’ A small variety was enjoyed more than a thousand years ago by the imperial court in Japan. Indigenous communities in what’s now Chile cultivated them for millennia before the Spanish conquest.

TWILLEY: So many strawberries, so many flavors.

EDGER: There’s one that I particularly like that tastes like a—almost like a little pineapple. It’s wonderful. It’s actually yellow in coloration. It’s very tropical tasting, very small. The fruit’s maybe the size of a pinky nail, so it’s incredibly tiny.

GRABER: That pineapple-flavored pinky-sized fruit is one of dozens of species of wild strawberries that have been around for millions of years. But the cultivated strawberry you can buy at the store? That’s super young.

STEVE KNAPP: That modern strawberry really only has 300 years of domestication history. It originated from chance hybrids from plants carried from the New World to the Old World by early explorers. And so it’s a hybrid between two wild species actually.

TWILLEY: This is Steve Knapp, he’s director of the strawberry breeding program at the University of California, Davis. He and Patrick recently collaborated on a project to decode the genome of the strawberry.

GRABER: What’s weird is that for most fruit, we have no idea when the fruit we eat today emerged. It probably took place over thousands of years, it took a lot of time and generations of mixing of different plants. But for the commercial strawberry, we know precisely where and when it was born.

EDGER: It occurred from a collection—a voyage to Virginia about, you know, 300 years ago. Wooden ships, collecting strawberry of one of the progenitor species called Fragaria virginia. It was brought back to France and then later there was a subsequent expedition where they collected the other species, Fragaria chiloensis from Chile, and then brought it back to France as well. And then, in a known greenhouse in Versailles, they accidentally hybridized. And then all of sudden they saw this massive strawberry emerge. And that really transformed the strawberry industry and what strawberry people eat.

TWILLEY: All the sudden, bingo: big conical red berries, rather than tiny little round ones.

GRABER: The new berries were hardier, too, which was a big deal. And they still tasted amazing.

TWILLEY: The British writer Samuel Butler was sufficiently moved to write “Doubtless God could have made a better berry, but doubtless God never did.”

GRABER: Samuel, you and I have something in common. And Samuel Butler could have enjoyed those heavenly berries for longer than in the past. Because the wild strawberries he’d have eaten otherwise—they were the very definition of ephemeral.

EDGER: They also have this quality that’s referred to as they melt. And so if you pick a wild strawberry, they will, like, melt in your hand. You can see them melting.

GRABER: These larger, less melty strawberries’ first home was in the northwest corner of France; the growers there supplied the markets of Paris and London. The farms were near the coast, and the region had a lovely marine environment with mild temperatures year round. Sounds like—

TWILLEY: The gorgeous coast of the gorgeous state that I am lucky enough to live in: California!

KNAPP: California is really blessed with this wonderful Mediterranean and subtropical climate mix. We also have good alluvial plains and flat areas where, you know, flowers and strawberries and lots of other crops thrive. We just have this ideal mix of temperature, the ocean cooling effect, and arable land.

GRABER: Wild strawberries might have been adapted to all sorts of environments, but this new breed of strawberry, it had finally found the perfect home. California had everything the strawberry could desire.

JULIE GUTHMAN: So the reason that California has become such an important place in the strawberry industry is it has these two kinds of natural advantages.

TWILLEY: Julie Guthman is a sociologist at UC Santa Cruz and she’s the author of the new book, Wilted.

GUTHMAN: Strawberries like sandy soils and they like temperate temperatures. And so most of the strawberries grown in California are grown very close to the coast, within three miles. People who’ve experienced summer on the Pacific coast know that summer like today, it starts foggy in the morning and warms to a nice 70s or so in the afternoon. So it’s never very hot. And so for the strawberries it’s like an eternal spring. And many other regions just don’t have those natural advantages.

TWILLEY: Blessed with these natural advantages, the California strawberry industry gets going. By the early 1900s, it’s already starting to be a serious business, although growers are still mostly only selling to the San Francisco market.

GUTHMAN: And when they first grew strawberries in California experimentally, they’d often grow them in between rows of apple trees. Strawberry farming then was still fairly small-scale, the strawberries were mixed in with other crops on the farm, and you could only get them a few weeks a year. They were a treat.

TWILLEY: So we’ve met the hero of our story: the California strawberry. But now we have to meet the villain. Its name is wilt.

GUTHMAN: So wilt refers to a problem of soil disease that comes from soil-borne fungi that get into the plants’ tissues and clog them up and disable that plant from being able to uptake water and nutrients and causes them to wilt.

GRABER: Julie’s book Wilted is, yes, largely about the meeting of heroic strawberries and the villainous wilt. The fungi is technically known as verticillium dahliae. And it’s bad for a strawberry plant.

GUTHMAN: It may still produce strawberries but it may not produce any. Often the wilt doesn’t happen till late in the season and so growers might get strawberries at the beginning of the season, and then they’ll see the wilt and they’ll get a less of a harvest.

TWILLEY: Now it’s not like wilt saves up all its evil powers to attack the strawberry. This is not personal.

GUTHMAN: It affects many, many plants. Tomatoes and potatoes and cotton and lettuce. Probably many, many others. I think there’s maybe over 150 plants are host to the pathogen.

GRABER: So wilt can kill a lot of crops. But it doesn’t sound too smart to kill off the plants you colonize.

GUTHMAN: It’s a bad evolutionary strategy for sure for a fungi to kill its host. And so you know in most settings something like verticillium is more of a parasite on its host.

TWILLEY: But in the strawberry situation, it does make sense for wilt to kill its host. Because the farmer is just going to come along and plant another strawberry plant in the exact same spot next season. There’s no penalty for killing your host.

GRABER: And so, by the 1920s, when the strawberry industry in California had started to grow, they also started seeing problems. Fields of strawberries would just all die.

TWILLEY: Farmers had no idea how to fight the wilt.

GUTHMAN: That didn’t help. For instance they used to leave strawberries in the ground for a very long time. Because strawberries will continue to produce. So if you don’t rotate those strawberries elsewhere the fungi will persist in the soil and reappear every year.

GRABER: And then on top of that, the farmers watered more heavily to try to revive their wilting plants, but verticillium actually loves damp soil. So that made it worse, too.

TWILLEY: So… maybe the strawberry is not going to make it big out west after all?

GRABER: But wait, World War 1 to the rescue.

TWILLEY: Specifically, tear gas.

GUTHMAN: And chloropicrin was tear gas. It was used to gas soldiers in World War One. When people are exposed to chloropicrin, they—their eyes tear and they want to vomit. And so what would happen is enemy troops would spray chloropicrin and soldiers would pull off their their gas masks to vomit and they’d be exposed to the full array of lethal chemicals.

GRABER: And then they died. Lovely.

TWILLEY: But, so did all the insects! Some bright spark noticed that yes chloropicrin caused crying and vomiting, but, also, there was a noticeable shortage of bugs in the areas where it was used.

GRABER: After the war, there was a lot of chloropicrin left over. So an entomologist started testing it on soil and found that, yes, it worked to kill bugs—but it also killed crop seeds, so he recommended waiting after using it before planting.

TWILLEY: Now, chloropicrin was super toxic, it smelled bad, and it made people really nauseous when they used it. But, at the time, there were a lot of scientists seeing whether weird left-over chemicals could be useful in the fields

GUTHMAN: Yeah, there was a lot of experimentation with chemicals. I mean it was such an imperative to control disease and pests. And I don’t know that there was a lot of public reaction to what the long-term effects would have been.

GRABER: Julie wrote in her book about a pineapple scientist in Hawaii who got a shipment of fifty-five gallon drums filled with chemicals, they were all waste products from Shell Oil’s petrochemical research.

TWILLEY: It was like Christmas morning. He went out, dug holes in the pineapple field every fifteen inches, poured in these random liquids, and waited to see what died.

GRABER: And a lot of creatures did. Dow Chemical heard how impressive those field trials were, they figured out what in the chemicals was doing the killing, and today that chemical is still in use in agricultural fields to kill tiny worms.

TWILLEY: But not strawberry fields. For strawberries, the magic bullet was chloropicrin—that’s the tear gas—but specifically chloropicrin used *in combination* with a chemical called methyl bromide

GRABER: Methyl bromide was first developed as a flame retardant, but then quickly scientists figured out that it could wipe out insects, too. In fact it was used in the Second World War to delouse soldiers.

GUTHMAN: So those two chemicals used in combination were the ones that the university scientists came upon in the 1950s, together they worked really well to control verticillium wilt.

TWILLEY: Like the pineapple scientist, California strawberry farmers injected this combination into their soil. Both chemicals were toxic, but methyl bromide was better at moving through soil, and chloropicrin had a noticeable smell, which was a helpful warning sign. And together—they fumigated the soil.

GUTHMAN: Well they, you know—sometimes they call it disinfestation, sometimes they call it sterilization. It kills a lot.

GRABER: Today we call those particular chemicals fumigants. They fumigate the soil. As Julie said, they kill nearly everything in their path. Including wilt.

GUTHMAN: Starting in the 1950s, growers started to fumigate instead of doing other techniques to control wilt. And by the 1960s, fumigation was a widely used practice.

TWILLEY: It wasn’t just that these fumigants stopped the strawberries from dying from wilt. Turned out injecting the soil with poison had other benefits.

GUTHMAN: Well, it had a tremendous effect on yield. I mean, after growers started using these chemicals combined—yield increased 20 or 30-fold. Huge increases. And part of it is like they don’t even know what was working about it. I mean, certainly they were losing less fruit to just the wilt, but they believed that there was something in the mix of these chemicals that was having an effect way beyond controlling wilt. That was giving it some sort of boost.

GRABER: Unsurprisingly, nearly all strawberry farmers started to fumigate. You kind of had to—banks wouldn’t even lend to farmers who didn’t. Because it was kind of like an insurance policy; you basically knew you’d likely have a successful crop if you fumigated.

GUTHMAN: And so growers who didn’t fumigate just wouldn’t stay in business very long. I mean there is a cost to fumigation and today it’s very expensive but pretty much everybody adopted it.

TWILLEY: So it’s the 1950s, and our hero the strawberry has had to get in bed with a couple of shady characters. But it seems like nothing can stop it now!

GUTHMAN: So fumigation did solve a whole lot of problems for growers and allow them to focus on a lot of other things including breeding for other qualities. They didn’t have to breed for disease resistance anymore. So it became all about breeding for yield and ship-ability. You know, in other words, a berry that wouldn’t rot.

GRABER: And then really quickly in the 1950s, after breeders turned away from wilt worry, they had a big breakthrough. They were interbreeding cultivated strawberries with a wild plant and they brought in a useful gene—

KNAPP: That had a really profound effect on changes in production, and it’s called day neutrality, but it’s a gene that allows the plant to flower under long days.

TWILLEY: This is Steve again, our strawberry breeder. And for the strawberry, this day neutrality gene is like winning the Triple Crown. Now you’ve got a strawberry that can grow year round, you’re breeding it to be more and more productive and long-lasting; meanwhile, your fumigants are taking out wilt and also boosting production. And, just as an added bonus, it’s the 1960s 1950s and pretty much everyone in America now has a shiny new refrigerator in their kitchen. Strawberries for the win.

GRABER: And so strawberry farmers bought new land. They planted more and more. They planted the strawberries year-round, no need to rotate crops because the strawberries never died.

GUTHMAN: And it created this surplus of fruit. I mean lots and lots of fruit. And so the California Strawberry Commission, which is the main industry group that supports research and marketing for strawberries, has had to do a lot to market strawberries because there’s so many grown. And so they’ve done all sorts of marketing campaigns. They work with retailers to feature strawberries in the front. They’ve done advertisements to encourage you know to tell people that strawberries are important or healthy or good for you or your kids’ll love them or that they’re antioxidant. And so there’s been a lot of work behind the scenes to get consumers wanting those strawberries. Productivity came first and then they had to figure out how to market them.

GRABER: And it worked. Strawberries are the most popular berry in America. Kids seem to love them. They’re in all sorts of processed food snacks. They’re everywhere.

TWILLEY: The strawberry came out west to make its fortune, and it has. Is that the end? Are we done, Cynthia?

GRABER: Well, Nicky, you and I have been making Gastropod episodes for five years now, and we both know—and you listeners know—that the story’s never quite so pretty. Because all those fumigants that all the strawberry farmers use to clear out the soil before planting? Well, maybe it won’t shock you to hear that they have some pretty serious downsides.

TWILLEY: Downsides! You know you want to hear all about downsides. And, of course, how our hero the strawberry might yet be able to overcome them.


TWILLEY: There are a lot of rules and regulations around fumigation that are designed to make it totally safe. For starters, it’s not like these chemicals are just sprayed on the field.

GUTHMAN: It’s a below-ground treatment and growers are no longer allowed to do it themselves. They hire out companies. There’s one company that does about 95 percent of the fumigation in California. The fumigation company has a rig and everybody suits up in this you know hazard protection equipment. And they go through the field and inject it into the soil and then cover it with plastic. And no one’s allowed to—supposedly allowed to go near that for several days after fumigation.

GRABER: Sometimes of course the plastic tears, and people do get exposed to the chemicals. It’s also an issue with communities that live near the farms.

GUTHMAN: There’s also people who after the fumigation takes place, there’s people who go round and shovel and they often do not wear protective equipment. So there’s all sorts of potential for exposure.

GRABER: Chloropicrin was, of course, tear gas, and it causes headaches and nausea and dizziness. If you’re exposed over the long-term, it can cause lung damage, and maybe cancer.

TWILLEY: Chronic exposure to methyl bromide is also not a good idea. High doses will kill you, but constant, low-level exposure damages your nervous system, it damages your liver, kidneys, and lungs. It’s carcinogenic. And scientists have found that pregnant women who live within 3 miles of fumigated fields have smaller babies, with lower birth weights and smaller head circumferences.

GRABER: Of course the protective gear and the plastic cover and the waiting time before planting, that’s all supposed to protect farm workers and people who live near strawberry fields. But Julie says that doesn’t always work.

GUTHMAN: This is a super contested thing. The strawberry industry thinks these accidents are unusual and hardly happen anymore. And if you talk to public health or farmworker communities they’ll tell you that it happens all the time and they don’t get reported in part because people don’t want to be deported or whatever.

TWILLEY: To be clear, what’s contested is how common exposure to fumigants is, not whether that exposure is a bad thing.

GUTHMAN: Most agree right now that they’re pretty toxic. The question is is whether the existing mitigation measures are effective enough at preventing toxicity to get to humans.

GUTHMAN: And again the degree to which these fumigants affect the plant or affect the pathogen is something that’s very little known about.

TWILLEY: Obviously, when you kill everything in the soil, you’re killing good things as well as the wilt. And Julie says that may well have led to the emergence of new strawberry diseases.

GUTHMAN: Fumigation pretty much controlled verticillium wilt. But in the past 15 or so years there’s been new pathogens that have emerged in the strawberry fields. But it’s also possible that those pathogens were there all along and appeared because of the changes that fumigation and the whole system did to the relationships between the plants and soils and diseases.

GRABER: And these are not the only problems that fumigants cause. Back in the 1980s, everyone was all worried about the hole in the ozone layer that was letting in more and more UV light that would kill plants and give everyone skin cancer. If you were around then, you might have thought your fridge and your aerosol hairspray were the biggest culprits—

TWILLEY: Which they were. But strawberries were to blame too.

GRABER: Specifically, methyl bromide. And so its use was phased out as part of the Montreal Protocol that was signed in 1987.

TWILLEY: At the time, there were other industries that also used methyl bromide. But they all had to figure out alternatives. They were given until 2005 to stop using it.

GUTHMAN: And the strawberry industry kept on lobbying the U.S. government to extend that deadline and they got what are called critical use exemptions. They said like we don’t have a viable alternative. Without methyl bromide the industry will die. And again that was the U.S. government really on behalf of the strawberry industry. They were the main group lobbying.

GRABER: But eventually even strawberry farmers had to give up their precious methyl bromide. The last year it was used was 2015.

GUTHMAN: There was another chemical that was developed to replace methyl bromide called methyl iodide. And that was super toxic, a neurotoxin. Probably causing thyroid cancer. It’s used to induce cancer in laboratory rats. It had all sorts of health effects related to it. And it was actually withdrawn from the market after a long activist battle and a lawsuit.

TWILLEY: So methyl bromide was finally gone, and there was no alternative. The strawberry industry predicted doom, gloom, and disaster. They said production would fall off a cliff.

GRABER: But it didn’t. Honestly, it’s mostly because strawberry farmers still use fumigants. They just use chloropicrin without its partner methyl bromide. It doesn’t spread in the soil quite as easily, but it still works.

TWILLEY: Basically, strawberry growers are hooked. They can’t grow on the same plot of land year after year without a fumigant. Which means they can’t grow in California without a fumigant.

GUTHMAN: I mean the cost of strawberry, of growing an acre of strawberries these days is at least $70,000. It’s probably more because labor costs have gotten really high for growers. And so to make a profit there, that means they’re making more than seventy thousand dollars an acre, which is extraordinary, compared to like something like rice which might be like fifteen hundred dollars an acre per year. So that’s a huge investment but the land is priced with the expectation that growers are going to grow this very high value crop.

GRABER: And so most California strawberry growers are still locked into this fumigant cycle, just so they can grow enough to afford the land they’re growing on.

TWILLEY: At this point, you might be starting to get a little worried. Like, oh my God, have I been eating tear gas along with my California strawberries? But researchers have tested and they have found that residues from fumigants don’t show up on the final fruit. So you are not exposed to fumigants, just the farmworkers and communities.

GRABER: Which is definitely already a reason to buy organic. But And there are plenty of other residues on conventionally grown strawberries. The Environmental Working Group lists the strawberry at number one of the dirty dozen pesticide-laden foods.

GUTHMAN: Oh, strawberries use all sorts of inputs. Fumigation’s just one of them. They’re one of the most chemical intensive plants that are—fruits or vegetables that are grown. They use all sorts of anti-fungals, they use miticides, because they have problems with spider mites. They use all sorts of inputs.

TWILLEY: In response to being named and shamed, over the past few years, the organic strawberry industry has grown. Even big industry leaders like Driscoll’s are converting more of their production to organic and not using fumigants in those fields.

GRABER: Frankly, though, I think even those organic Driscoll’s are pretty bland, since they’ve been bred to be stored and shipped long distances. As you all now know, I buy my strawberries in the summer from local farms that grow incredibly delicious, super aromatic strawberries. One of my favorite farms that grows strawberries is Mass Audubon’s Drumlin Farm. We visited with the head farmer Matt Celona.

CELONA: Right. So we are standing in our strawberry patch and we’re looking at eight thousand plants.

TWILLEY: There’s not fruit yet—it’s just like a carpet of green plants.

CELONA: Generally like the smell comes late in the season, like late June early July, and that’s when the berries are just ripening so fast and you have like this incredible sugary aroma. Smells like jelly, I suppose.

TWILLEY: Matt said that around when the fruit starts coming in, they use straw to keep weeds down. And they water the baby strawberry plants when they first go in the soil and that’s it. No sprays, no more irrigation, no nothing.

CELONA: We’d like to say like, hey, we we think the organic standard is kind of like a minimum standard and for us sort of unacceptably low. Like we want to be known for doing things beyond what’s required by the organic standard.

GRABER: And Matt said they have no problems with strawberry diseases. No issues with wilt. And lots of happy customers.

TWILLEY: But those baby strawberries? Matt gets them from a nursery. And that’s a whole different scene.

GRABER: Matt was shocked to hear about conditions in the nursery, and so was plant geneticist Patrick Edger, and we were too. But before we tell you about how those strawberry baby plants are grown, first we have one more sponsor to tell you about.


TWILLEY: Here’s the thing. Strawberries aren’t grown from seed—there’s too much natural variation. They’re cloned from runners—just pieces of the strawberry vine. And these runners are grown into baby plants at special strawberry nurseries.

GRABER: And those nurseries need totally clean stock for farmers in the U.S. and even in other countries. And so they managed to convince the powers that be that they should have what’s called a critical use exemption for methyl bromide.

GUTHMAN: It’s still allowed in the nurseries. I mean, I’ve talked to people New Zealand who use California varieties. And so because they haven’t found something that reliably keeps these plants disease free—and I think they have to, like, there can’t be any more than 5 percent of the plant can have disease or it becomes un-shippable.

TWILLEY: So this fumigant that is banned in the fields—every year, the strawberry nurseries apply for an exemption and every year they get one, and no one—even people who know a lot about strawberries like plant scientist Patrick Edger—no-one knows this.

EDGER: So actually that exemption is totally new to me. You know something I don’t know. Yeah. So—so nurseries that are propagating can use it?

GRABER: Yeah. It’s nearly impossible to buy starters from nurseries that don’t use methyl bromide.

EDGER: Huh. In glass houses or in the field?

TWILLEY: In the field.

EDGER: Huh. Yeah that’s totally new to me.

GRABER: So Patrick was shocked, and Matt was shocked, too. He didn’t even know that strawberry farmers in California use fumigants, because his farm operates so entirely outside that monoculture culture. So the idea that nurseries might use methyl bromide? Not on his radar.

CELONA: No, because I don’t know about this fumigant thing that you’re talking about. So yeah, it never crossed my mind. Wow. So, yeah, good to know.

TWILLEY: Like we said, Drumlin Farm holds itself to a higher standard even than organic.

GRABER: Matt buys his baby strawberries from a nursery nearby. He didn’t know how they grew those plants, as I said, he didn’t even know that anyone would ever fumigate strawberry fields. But I emailed that nursery, and, yes, they use methyl bromide.

TWILLEY: Even the best intentioned strawberry farmers don’t really have much of an option here. Almost all baby strawberry plants are grown using methyl bromide. In New England, according to industry sources, there are no commercial nurseries growing baby strawberries without fumigants. It’s like this dirty secret.

GRABER: But there are solutions that could wean the strawberry industry off fumigants—strawberry farmers who use chloropicrin, and strawberry nurseries who are using methyl bromide, too.

TWILLEY: In an ideal world, the strawberry industry would quit fumigants. Right?

KNAPP: Could I be un-courageous? Could I not answer that?

GRABER: Because Steve Knapp is a strawberry breeder who works with the entire strawberry industry in the state of California, organic and conventional, he really did not want to answer that question.

KNAPP:You’re just not going to let me be uncourageous, are you?

TWILLEY: Sorry Steve!

KNAPP: You know, I mean, I have deep personal feelings about our planet, right? And there are things I would like to see happen. But I really I also understand the challenges that people have to produce food. It’s you know—my view is hopefully my contribution to the world here will be to make that less necessary.

TWILLEY: Conventional strawberry growers love fumigants. So Steve’s caution is completely understandable—Patrick was the same way. But for farmworkers sake and for the environment—and honestly, maybe for the future of the strawberry itself—the industry *needs* to wean itself off them. And there are some ways it could start doing that.

GUTHMAN: One method that works is is very agro-ecological, like where you rotate strawberries with other crops or with compost. And/or with mustard seed and broccoli. Broccoli has mild fumigation properties. But in those integrated systems strawberries are a minor crop and you can only put strawberries in the ground like every three or four years because you’re using those other crops—you’re using fallows or or compost or cover crops or brassicas to fend off the pathogens. So that works but it doesn’t work—you can’t grow as many strawberries and you certainly can’t grow in the monocultures that we see in California.

GRABER: This integrated system is how Matt farms at Drumlin. And he has no wilt problems. But part of why he can afford to do that is because even though the farm is on pretty valuable land close to Boston, that farmland can never be sold to a developer. But strawberry farmland in California is incredibly valuable coastal property. And strawberries bring in a lot more money than broccoli does.

TWILLEY: In Europe, most strawberries are grown without fumigants—but also without soil.

GUTHMAN: In Europe, they grow a lot in greenhouses. And that’s certainly one of the directions the strawberry industry is experimenting with. If not full greenhouses than what they’re calling field level hydroponics, where they are growing strawberries in trays filled with soilless substrate. So rather than using soil which is is the medium of the disease, they use coconut coir or peat moss.

TWILLEY: Of course, in Europe, these Dutch greenhouse-grown varieties are also infamous for tasting of precisely nothing.

GRABER: Plus, California growers aren’t interested in soil-free greenhouses.

GUTHMAN: It’s super expensive. It’s a lot of infrastructure to use waist-high trays. They haven’t yet found varietals that really works well in those systems in California because so many of these cultivars have been bred to be in fields.

TWILLEY: And remember, the only reason the strawberry moved West is because of California’s natural charms.

GUTHMAN: But individual growers have nothing to gain by or little to gain by this because their biggest advantage is again the sandy soil and the climate. And once you move toward soilless systems and particularly if you move toward indoor growing, what’s the advantage of growing on this very expensive land in California? They could move these berries closer to urban markets.

TWILLEY: In other words, if you’re going to grow strawberries for New Yorkers in a greenhouse, that greenhouse may as well be in New Jersey.

GRABER: Farmers could use a non-chemical type of soil fumigant—there are a number of different techniques. One is called steam disinfestation, which is what it sounds like.

GUTHMAN: So rather than using a chemical, disinfesting in the field with steam injection. Which works OK. It works well on weeds but it’s super expensive and time consuming. There’s also a technique that’s been—that a lot of organic growers are using called anaerobic soil disinfestation where you’re mixing in a carbon source like molasses or rice bran into the fields and then flooding them with water and covering them with plastic and that’s kind of drowning out the pathogen, creating anaerobic conditions so it can’t replicate.

DAN NELSON: And we found that to be working very well, in particular in the nurseries where the temperatures are high. The efficacy of that treatment works really well.

TWILLEY: That last voice, that’s Dan Nelson. He is one of the co-founders of the only nursery that supplies baby strawberries that haven’t been grown using chemical fumigants. Driscoll’s—that’s the biggest player in the strawberry industry— they recently began to supply some of their growers with organic baby strawberries. But for non-Driscoll growers, Dan’s company, Innovative Organic Nursery, that’s their only option to avoid baby plants grown with methyl bromide.

NELSON: There’s a lot of other techniques that we’ve explored. we’ve got cover crops that we’re playing with. And we’re exploring almost anything that’s available to us. You know, we’ve spent the last four years effectively testing all of the options out there

GRABER: Dan’s baby strawberry plants so far are, unsurprisingly, more expensive than the methyl bromide fumigated ones. And Dan has to actually work even harder to have disease-free baby strawberries because he knows organic ones are an unknown risk for farmers.

NELSON: You know, essentially we’ve got to make sure that we don’t deliver something that is that is problematic for the growers. So yes, there are options but none of them are—have been really scaled up and a lot of them have significant disadvantages, not least of which is cost.

TWILLEY: In the meantime, there’s another path our strawberry hero could take. After all, we have bred strawberries that are bigger and last longer and are more prolific and bear fruit all year round. Why not breed strawberries that resist disease?

KNAPP: First of all, the strawberry is a fascinating species. It’s called an octoploid. So it has four different plant genomes that came together to make what we call the modern strawberry everybody’s familiar with.

GRABER: Fascinating, sure, but those four different plant genomes, or eight different sets of chromosomes, it means that breeding new strawberries is even harder than for other species that have fewer chromosomes. There’s so much genetic variability, the new breeds could kind of go anywhere. It’s hard for Steve to find the trait he wants and keep it in his new strawberry plant.

TWILLEY: We humans have just two sets of chromosomes in our genome that we inherit from our parents— one from each. In scientific terms, we’re diploids. But plants tend to be hoarders and they hold on to extra genomes when they interbreed. Still, eight sets of chromosomes is a lot. And that’s why it’s only just this year that scientists managed to publish the strawberry genome. Patrick and Steve and a couple of colleagues, specifically

GRABER: To assemble the octoploid strawberry genome, Patrick and Steve had to develop new tools to figure out how to put together genetic code for a plant that has eight sets of chromosomes. They didn’t publish the very first example of an octoploid—another team did that with the sugar cane genome earlier in the year.

EDGER: That was, you know, it’s also an octoploid. But really prior to that people really stuck with diploid organisms because how difficult it is. To even assemble something that only has four copies or a tetraploid was very, very difficult. And so for us to go on a mission to try to put together an octoploid, really, and develop tools to allow us to do this, was really pushing boundaries.

TWILLEY: And it took them a lot longer than usual. Assembling the genome of a diploid plant—that takes Patrick a couple of days, maybe three. Then maybe another month or so to make sure it’s all in the right order.

EDGER: The octoploid strawberry genome took us about two and a half years.

GRABER: It might have taken an extra long time, but it worked! They were able to assemble the strawberry genome. Which will help with breeding the strawberry of the future.

KNAPP: You could think of the genome as the foundation of a house. Without the foundation we’re not going to get the walls and the roof and the windows. And that the genome is is like a roadmap. If we don’t have that we can’t locate where a particular gene is. But once we know that it provides us with a strategic way to use DNA barcodes.

TWILLEY: Steve used to have to make crosses based on what he knew about the strawberry parent plants traits, and then he’d just have to wait and see. Now, using the genome he and Patrick assembled, he can predict which crosses will give him the qualities he’s looking for, and then test the baby plants right away to see if he’s right.

GRABER: And this is a really big deal to a really big business.

EDGER: For breeding programs, strawberry is a high-dollar crop to the U.S., worth about between somewhere between three to four billion dollars every year to the U.S. economy. And there weren’t really any tools available to guide breeding programs, to make strawberry bigger or better or more aromatic or higher disease resistance. So there were really no tools available as there are for soybean and corn and so on.

GRABER: But now that they have this tool, Patrick and Steve can use this information to breed new varieties that meet what growers need today—and, now that fumigants are being phased out, growers want plants that are resistant to diseases.

EDGER: Yeah. Oh yeah. We found hundreds of genes that are key candidates for disease resistance against a number of really important pathogens.

KNAPP: But you can imagine if you if you put the sort of the Venn diagram of all it, took all of it together, you know—be high yield, complete resistance to all pathogens. Wonderful flavor every month of the year. And so of course those are the ideals we’re shooting for.

TWILLEY: But, in strawberry plants as in life, turns out you probably can’t actually have it all.

EDGER: Of course, the plants don’t have infinite amount of resources. Some metabolic resources are now going to have to be devoted to defending themselves against some pathogens. And so there’s 100 percent going to be a trade off between yield, fruit quality, and disease resistance that people didn’t have to worry about before.

GRABER: It takes energy—metabolic resources, as Patrick says—for the strawberry to defend itself. And that metabolic resource has to be diverted away from something else. Like maybe growing bigger.

EDGER: Maybe there is a slight size—decrease in the fruit size but the aroma and the taste is going to be good—is going to be improved. But ultimately that I think will then have to be decided by consumers. But personally as a consumer myself I would be OK with a fruit that’s maybe 5 percent smaller if it’s more aromatic.

TWILLEY: Or if doesn’t require treatment with toxic chemicals.

GRABER: Yep, me too.

TWILLEY: Patrick has gone on to sequence the genomes of a bunch of wild strawberries. He’s found disease resistance genes in them that have been lost from the commercial variety we all eat.

EDGER: It’s going take us maybe a few years to be able to stack all that resistance to create new cultivars. But I’m confident that it could be done without soil fumigants

GRABER: And Patrick’s not just interested in resistance. He thinks that growers could breed a variety of strawberries, kind of like how you can buy apples that tastes pretty dramatically different from one another. Some are good for pies, some are good to snack on, some are better for applesauce…

EDGER: And of course it’d be nice, yeah, to have some diversity, right? Where we can have really a spectrum of different strawberries with different attributes. Some that maybe pair nicer in salads or some that may pair nicer in desserts or in cakes and so on. Or to eat plainly. Right? So I certainly envision a future where that’s possible.

TWILLEY: Of course, you’re not going to see all these new strawberries in the store next summer— even with the genome it still takes years to breed a winner and then grow up enough plants to introduce a new variety. But Steve and Patrick are definitely enjoying this next step in the strawberry’s journey.

EDGER: So you know it’s—so the greenhouses and particularly growth chambers where—these are highly climate controlled places where we grow strawberries. They’re sealed from the environment. Right. But as soon as we open them, like, there’s a blast of the most lovely—I mean, it’s exciting. I look forward to opening a growth chamber and getting blasted with the smell of strawberries. I look forward to that one or two times a day where I go and just check on all my plants and it’s really—it’s just really nice.

GRABER: Steve isn’t just studying strawberry genomes, like Patrick is, he’s breeding new varieties. So he actually has to eat them. A lot of them.

KNAPP:And I just eat them fresh. I just eat them fresh. I don’t do anything with them. I do make one Italian dessert with them, yeah, with sort of Madeira and crème fraîche. But, anyway, that’s the only way I ever doctor em up.


TWILLEY: If you haven’t started drooling yet, I don’t know what’s wrong with you. Even I am and, like I said, I’m really more of a raspberry girl. But I’m going to try Steve’s recipe—and you can too—he shared it with us so it’s on our website at

GRABER: You might be wondering where this whole story leaves you in terms of eating strawberries. I totally love them, and I do think you should enjoy your strawberries! But I’d recommend you get them in season as much as possible and as close to you as possible. First of all, they’ll taste a lot better. Second of all, you can find out how they’re grown and try to buy from someone who grows them on an integrated farm, like Drumlin. Organic practices are definitely the way to go with strawberries.

TWILLEY: And if you really want strawberries all year round, Driscoll’s is starting to use organic baby strawberries too. But this is really a chance to talk to your farmer and ask them about their nursery. Organic baby strawberries are available from Innovative Organic Nurseries, and it’s not a bad idea to put pressure on other nurseries to clean up their act.

GRABER: Thanks so much this episode to Steve Knapp, Patrick Edger, Julie Guthman, Matt Celona, and Dan Nelson. We have links to their research and companies and books on our website,

TWILLEY: There’s another reason to go to gastropod dot com and that is to get in on our awesome birthday gift exchange. You support us at any level before the end of September, our birthday month, and we give you a super special prize! If you prefer Patreon, we’re at

GRABER: And we haven’t forgotten about those of you who have been long-time supporters of the show, you’ll be hearing from us in honor of our birthday, too! As we say frequently, we are just a two-person team here at Gastropod, and we could not do what we do without all of you!

TWILLEY: And guess what, because we just love to party, our next episode is also going to be a celebration! This one takes us south of the border. Any guesses?