Rise Of The Plant Destroyer

The first reports in Europe came from West Flanders, Belgium, although it most certainly started elsewhere. It was August 1845, and the potatoes were dying. Dark flecks would develop on the leaves of one plant, and within days the entire field was destroyed. The stems seemed almost melted and the leaves hung dead, charred and black, as if an invisible fire had ripped through the land. When the potatoes themselves were dug up, they’d been reduced to a slimy ruin.

Within weeks, the disease had spread across Europe into the Netherlands, Germany, Switzerland, Poland, France and across the English Channel to the British Isles. When a Miles Joseph Berkeley of England received infected leaf samples from a friend in Paris, he remarked that his own crops in Northamptonshire were “never more abundant or finer.” In less than a week, the potato fields around his county too were blackening.

Crop diseases had struck before but never with such terrifying speed. Panic took hold across Europe, and theories began to spread that the disease was caused by static electricity generated by the new steam trains, or vapors of “bad air.” Or perhaps it was simply a judgement from God.

Nobody knew what to do — leave the potatoes in the soil or dig them up? Expose them to light or keep them in the dark? Smother them in salt or soak them in chlorine? Also: Could these diseased spuds still be consumed? For three whole days, Monsieur Bonjean, a man from the French town of Chambéry, exclusively ate rotten potatoes and drank water boiled with them to see if it caused any ill effects. He survived but reported a disgusting taste and a “disagreeable heat oppressing the chest.”

In the preceding centuries, new trade routes had uprooted the potato from its native South America and shipped it to Europe. Just as it had supported the rise of the Incan Empire, it supported the rise of Europe, becoming a vital food staple from the 1700s onwards. It was a durable crop, easier to prepare than bread and highly nutritious. Monarchs promoted the potato to their populations as a solution to famine and food riots. And because it grew underground, it was rarely damaged or pillaged during Europe’s endless wars. 

In France, Louis XVI and Marie Antoinette even began wearing potato blossoms as accessories, and the royal gardens of Tuileries Palace were planted with potatoes instead of flowers. In Prussia, King Fredrick II ordered his government to distribute free seed potatoes with growing instructions, and Nicholas I did the same in Russia. Populations across the continent boomed partly as a result of the potato’s rise, and the historian Charles Mann likened its impact on Europe to the invention of the steam engine. If archeologists arranged human history using organic rather inorganic materials, this would have been called the Potato Age. 

Nowhere took to the potato quite like Ireland, where the cool, damp climate was especially suited for its proliferation. The population nearly doubled between 1800 and 1845. The Irish remained largely poor but healthy, and around a third were sustained on nothing but potatoes and milk. 

But then on Sept. 13, 1845 The Gardeners’ Chronicle in the U.K. announced the disease had “unequivocally declared itself in Ireland. The crops about Dublin are suddenly perishing.” Irish folk archives of the time report a dense fog that lasted days in the west, and a terrible stench that filled the fields. That year, the disease wiped out a third or more of Irish potato crops, but the following year, it was total devastation. 

“Wandering beggars, roadside deaths, rising crime rates, poorly attended burials, widespread panic about contagion and mass evictions were commonplace throughout most of the country,” wrote the historian Cormac Ó Gráda. “Evictions, by forcing migration, exacerbated the problems. … There were many such accounts of bodies left unburied; others described survivors dragging corpses unaided to cemeteries, and people not yet quite dead being lowered into communal burial pits.”

There’s no doubt that Britain’s neglectful colonial rule over Ireland during the famine years — fueled by the ideological rhetoric of Prime Minister John Russell, as well as leading figures like Charles Trevelyan and Charles Wood — worsened a crisis initiated by plant disease. Tens of thousands died across Northern Europe, but that was little compared to Ireland, where it is estimated that as many as 1.5 million died of disease, hunger and fever following the crop failures, most of them the country’s poorest. And between 1846 and 1855, 1-2 million more emigrated, a mass movement of people that, until then, was perhaps the fastest in human history. To this day, Ireland’s population has not returned to the level it was before the famine.

At the same time as potato crops were failing across Europe, halfway across the world, chestnut trees in the southeastern United States were dying in great numbers, so many that hillsides once covered in majestic greens, reds and yellows turned a dull grey. They were perishing too in western Italy, where locals noticed what they called “mal dell’inchiostro” (“ink sores”): foul-smelling wounds amid the trees’ ridged bark oozing a black liquid. 

Nobody knew it then, but the potato famine and what would become known as chestnut root rot were the result of closely related microorganisms. The world had shrunk, and devastating microbes were traveling to lands they had never visited before, attacking plant species that were unprepared to fight back. 

This genus of microbes contains many different species that behave in many different ways — the ones that attack potatoes and chestnut trees are only two of perhaps hundreds of others. But in time scientists would come to realize they were all related, and they grouped them together under one carefully named genus: Phytophthora. In Greek, it means “plant destroyer.”

“Every aspect of human society and every part of the natural world is affected, for good or ill, by the activities of tiny unseen microbes — bacteria, viruses, fungi and protozoa,” wrote the British writer Bernard Dixon. Microscopic organisms are the most abundant form of life on Earth, filling the air we breathe, water we drink, soil we walk on and food we consume. They make life possible, and have been since the very beginning. Many of them are also the waste disposers of our planet, without which we would be surrounded by ever-growing colossal mountains of the dead. 

At some point in their approximately four-billion-year existence, certain groups of microbes discovered the evolutionary niche of living on or inside other living things. Your body is a good example: A couple pounds of microbes, more or less, live inside your mouth, your eyes, your gut, on your skin, all carrying out their own independent tasks. You are a complex assemblage, more “we” than “I.” 

Most plants are no different. Microbes live on and in plants, and in the soil from which they grow, weaving their way into their cellular structures to create an interface where they exchange everything from nutrients to water to signaling compounds.

“We know from the oldest fossils that when plants arrived on land, they already had fungal structures inside their cells,” Sebastian Schornack told me, as I admired a colorful tank of shell-dwelling cichlid fish on the desk in his office. Schornack is a plant scientist at the Sainsbury Laboratory at the University of Cambridge. His research focuses on how plants and microbes live together, sometimes collaborating, other times competing. “Plants consider this so important they have maintained a whole set of genes to engage with symbiotic fungi. But if you have a whole system that allows someone into your home, the question is: Are there others exploiting it?”

In an era of animal pandemics — tuberculosis, smallpox, COVID-19 — it’s easy to overlook the fact that plants also experience them, and they can have an equal or more devastating impact on human society. Humans of course live in complete entanglement with plants, and our incessant struggle to manipulate and control them has defined modern civilization. Plants provide over 80% of all the food we eat and are the primary source of feed for our livestock. Their materials are in our fuels, clothes, medicines and the structures we build; even our hands are shaped by millions of years of climbing trees. Trees cover around 30% of the world’s land and produce much of the oxygen we breathe, not to mention store the carbon we need to remove from our overheating atmosphere. What affects plants, in other words, affects humans.

As the climate shifts and global trade quickens, plant diseases are becoming increasingly frequent, severe and widespread. Each year, pests and diseases rip through global food crops, where they cause losses of up to 30% of staple crop yields, and dramatically alter the Earth’s natural forest ecosystems. It was plant disease that made the once-dominant “Gros Michel” banana nearly commercially extinct (Fusarium wilt), turned the towering American chestnut into a mere shrub (Cryphonectria parasitica) and is currently threatening the future of coffee (Hemileia vastatrix). “There is basically always a plant disease pandemic ongoing,” said Schornack. “But most people don’t know it.”

For almost a century, scientists working on Phytophthora (pronounced “fi-toph-tho-ra”) thought they were dealing with a strange type of fungi. It looked like fungi and behaved like fungi, so it must have been fungi. But as technology improved and they were able to look deeper into the structure and behavior of the pathogen, they realized they were dealing with something different. In the 1980s, one scientist went so far as to suggest renaming it “pseudofungi.” “Let’s put it this way,” David Cooke, a scientist at the James Hutton Institute, explained to me over Zoom, “it’s as closely related to a fungus as you and I are to a pine tree.” 

Phytophthora descend from an ancient lineage of microbes known as oomycetes — a group that either absorb their food from surrounding soil or water or by colonizing the body of another organism. Oomycetes are most closely related to algae but evolved to form a motley crew of parasites. Like all microbes, they complicate our taxonomies by blurring the lines between animals and plants: Some of them attack fish and amphibians, others attack insects, but most, like Phytophthora, attack plants. 

“Essentially, they are like algae that have lost the ability to photosynthesize,” Cooke said. “They worked out it was easier to hijack their food from plants that are doing the work for them.” In 2000, scientists knew of only 50 or 60 Phytophthora species. Today some 200 have been discovered, and the number is still climbing. 

“Evil fungus?” I proposed to Schornack, who grimaced. 

“From a human perspective, it seems dark because it involves stealing or tricking,” he said. “But in an ecosystem, we need these mechanisms, otherwise we wouldn’t have the constant circulation of resources, like minerals and nutrients. … Parasitism is a widespread phenomenon that evolves in all parts of life. The interesting thing about it is that it always evolves together with the host. You have a coevolution where parasites try to steal and hosts try to defend. Both parties adapt their mechanisms to steal or defend.”

He directed me down wood-paneled corridors into one of the labs where his team works. Machines whirred and surfaces shone white. There were microscopes on each table, and one in a room of its own. It was so powerful, Schornack told me, that you could look into individual cells and watch proteins move around. 

He ushered me toward a shelf where a small, sealed Petri dish sat unassumingly. Inside, pressed against the lid, was a white fluff. “This,” he said, “is Phytophthora infestans.” It looked as if someone had captured a tiny slice of cloud, or gathered a fragment of cotton candy.

Of the hundreds of species of Phytophthora, some float through the air in droplets of water and attack plants through their leaves, fruit or bark; others swim in waterways and creep through the moisture in soil to attack roots. The Phytophthora infestans (P. infestans), which caused the crop failures that began the Great Irish Famine, is the poster boy of the oomycetes. It has been described as “the plant pathogen that has most greatly impacted humanity to date,” and remains among the biggest killer of potatoes and tomatoes worldwide. 

Over the last 200 years, sudden outbreaks of this globe-trotting fluff have damaged economies, influenced wars and sparked social unrest. For a while, humans even flirted with harnessing its destructive nature for our own uses. During and after World War II, Germany, Britain, France and America invested heavily in researching P. infestans as a tool of biological warfare that could destroy an enemy’s food supply. The appeal was its ability to spread far and wide, like radiation from a nuclear bomb, and when you look closer at how it works, you can see why warmongers desired it.

As a parasitic microbe, Phytophthora is formidably, elegantly designed to do what it does. It is able to have sex with itself, a reproductive process which eventually births ephemeral sporangia — imagine microscopic and colorless lemon-shaped spores — that float through the air, carried for miles by wind, rain and fog. Life continues for the sporangia if one lands on the leaves of a plant it understands, preferably a species of potato or tomato that hasn’t evolved disease resistance. 

Then, if the conditions are right — ideally damp and cool — the sporangium will, over the course of 30 minutes or so, swell up and burst open, allowing a hoard of tiny spores (known as zoospores) to come scuttling out. The tiny zoospores hover for a moment, as if coming to terms with what they are and what they do, before speeding off. They are incredibly fast swimmers, almost sperm-like, and propel themselves using two hair-like threads that they whip and beat in tandem to navigate the moisture on a leaf’s surface. Under a microscope, the zoospore appears like a demonically possessed tennis ball wielding two pipe cleaners.

The zoospore then grows a long germ tube that slithers and probes around for a weak spot on the leaf before punching its way into the plant’s flesh. Into this microscopic wound, hyphae grow: long branching pipes that maraud through the plant’s insides via the corridors of air between its cells. The hyphae poke finger-like haustoria (from the latin “haustor,” meaning “one who drains or drinks”) into cells, which begin sucking the nutrients from the plant. As the disease colonizes the entire plant, it secretes proteins that suppress its immune system and convince it that it is not actually dying. The plant, now nourishing the pathogen rather than itself, rapidly deteriorates and dies.

An observer would see black, brown or purple blotches on the leaves grow and spread, soon followed by white fringes of mold on the underside of the leaf. This mold is the pathogen’s final act. Under a microscope, the mold reveals itself to be a forest of thread-like filaments emerging from the pores, or stomata, on the underside of the leaf’s surface. Having sucked the life from the plant, these tiny trees grow and bear the fruit of a new generation of sporangia, ready to be carried away again, leaf to leaf, field to field, country to country. In certain conditions, P. infestans can also produce oospores — thick walled stalwarts that can survive freezing winters and reinfect new crops the following year. 

The British botanist and novelist E.C. Large described this ordeal in gory detail in his 1940 opus on plant disease: “If a man could imagine his own plight, with growths of some weird and colorless seaweed issuing from his mouth and nostrils, from roots which were destroying and choking both his digestive system and his lungs, he would have a very crude and fabulous, but perhaps instructive idea of the condition of a potato plant when its leaves were moldy with” P. infestans.

This entire process takes 48 hours or so, and every square centimeter of an infected leaf’s surface produces around 20,000 more sporangia per day. “Amplify that to an industrial crop scale and there are billions of these spores being produced very quickly,” Cooke said. 

Since the late 1960s, widespread forest epidemics as a result of Phytophthora have increased exponentially. Among the most virulent tree killers is Phytophthora ramorum (P. ramorum), which most likely originated in East Asia, and spread around the world via the global rhododendron trade, one of the many plants it infects. Like P. infestans, it is primarily an airborne disease that moves quickly. It was discovered in California in the late 90s — where it was given the name “sudden oak death” — and went on to kill around 50-70 million native oaks and tanoaks across the U.S. Then it turned up in Europe, and soon it had blown to Scotland.

On the outskirts of Dumfries, a town in southwest Scotland, I met with Alan Gale, the adaptation and resilience manager at Forestry and Land Scotland, a government agency responsible for conservation, timber production and managing and protecting a third of all the country’s forests. Gale was born and brought up in the area and has been working in forestry for 30 years. “All of my family work in forestry,” he told me. “We love trees.”

Unlike most fungi, Phytophthora have no mushroom or fruiting body that signal its presence. It’s ghostly, invisible to the naked eye, known only by the destruction it leaves behind. If scientists and foresters want to find it, they have to go looking for it. They can leave buckets out in the rain to collect water and analyze it for spores, or take samples of soil. Another method, which Gale retrieves from the trunk of his car, is a PCR test. Trees, just like humans, can take PCR tests. “It’s exactly the same as the ones we all now know,” he said. “You take your knife, take a little bit of bark off, put it in the little bottle of fluid, and give it a shake. We’ve been using these for five or 10 years.”

For the first 20 years of his career, Gale said, he had “no need for an interest in pests and diseases. It was something I thought about once or twice a year. … Now they’re having a massive impact.” As we drove through the countryside past fields of Highland cows, he pointed at vast swathes of brown forest rising up on the hills around us and even bigger stretches of dark stumps. “Dead,” he said, pointing at one section. “That’s dead,” he said, pointing at another. “In parts of south Scotland and west Scotland, it has been catastrophic.” 

In a world where the effects of climate change are sometimes dramatic, Scotland is mostly mellow: no severe droughts, wildfires or devastating storms. The impact is more subtle: Winters are a little warmer and a little wetter. But P. ramorum likes warm and wet winters. “Most larch are going to die in this area,” said Gale.

As is the case with all Phytophthora, there is no known cure for P. ramorum. And because infected trees become vectors of transmission, the official control method in Scotland is to cut down everything within about 800 feet of an infected tree. In the last 10 years, millions of larch across Scotland have been felled or put on a waiting list to be. In one area between the coast and Dumfries, the disease spread so quickly and so brutally that foresters, fellers and sawmills couldn’t cope. Felling and prevention tactics were simply abandoned, dead trees were left standing, and no woody materials allowed in or out. 

Phytophthora have extremely high evolutionary potential, and are known for their ability to overcome host resistance and jump to new species if the conditions are right. Until 2009, P. ramorum had never been found in larch — it was called sudden oak death for a reason. Scientists were bewildered to find it in larch, and they will be again if (when) it jumps again. The front line is moving north, and they are already felling uninfected larch just as a preventative measure.

Gale and I pulled into Dalbeattie Forest: around 2,700 acres of trees on granite upland. Larch are not native to Scotland: They were first introduced in the early 1700s, and are grown and cut for timber used in construction. They are allowed to grow for almost half a century, and in that time create vibrant forest ecosystems and communities. Bike tracks and walking paths weave through the forest floor; goshawks and red squirrels and many other animals have colonized the trees. At the forest gate, a startled roe deer dashed away as we approached. Gale walked with a crutch, having hurt his leg, but he scampered into the crunchy undergrowth and snapped off a branch with a crack that echoed around us. “The needles should all be flushing a lush green right now, for spring,” he said. “But they’re not.” 

I realized we were completely surrounded by dead trees. Some larch can live for 300 years and grow up to 130 feet tall, but a microbe smaller than a needle point can kill one in months. A cool breeze cut through the forest, and if our eyes could have seen the sporangia, they may have been gliding through the air: a blizzard of poisonous snowflakes.

Gale told me that foresters like him get great data on how much warmer and wetter it’s going to be in the future as the climate warms, and how that’ll affect plant life and forest ecosystems. What they struggle to plan for are the pests and diseases, he said. “We really don’t have a clue what’s coming at us.”

“What makes a native plant or animal or fungus abandon its companionable habits to carve a path of destruction across the landscape?” asked the anthropologist Anna Tsing in a 2018 essay on invasive species, from rice-devouring insects to frog-killing fungus to ocean-dominating jellyfish. Her essay was inspired by her work on Feral Atlas, a scientific research project that proposed the concept of “feral” ecologies: the unintended consequences of human activity that spiraled out of our control. Viruses, bacteria, fungi and chemicals that thrive because of human disturbance, spread via global trade flows, proliferate in dramatically changing climates and become uncontainable. 

Most plants can defend themselves against most pathogens, especially those that have coevolved together; they tend to reach a state of close competition in which the pathogen can steal enough to survive and reproduce, and the plant can defend itself well enough to stay alive and spread. “The result is that both sides are continuously adapting and counter-adapting to each other,” wrote the biologist Andy Dyer in his 2014 book “Chasing the Red Queen.” “In such an ‘evolutionary arms race’ there is no winner, only a never-ending race without a finish line.” In biology, this is known as the “red queen hypothesis,” named after a passage in Lewis Carroll’s “Through the Looking Glass” in which the Red Queen explains to Alice that in Wonderland, a person must run very fast just to stay still.

Problems arise when the incessant beat of global trade brings feral pathogens to new territories where species have not evolved the defenses to protect themselves. Thomas Jung, a scientist at the Phytophthora Research Centre, recalled travelling across Asia to trace the origins of Phytophthora cinnamomi. “In Taiwan, Vietnam and all across Indonesia, you are basically walking on Phytophthora cinnamomi,” he said. “It was in almost every soil sample I isolated. But there was no damage to the trees, because of coevolution. … It’s definitely there, but it’s a benign pathogen.” By contrast, when the exact same disease found its way to southwest Australia, it became a threat to national biosecurity, attacking around 40% of all native plant species. Scientists and conservationists there call it the “biological bulldozer.”

Plants have been moved around the world in huge quantities since the dawn of European colonialism. Timber, grasses, potatoes, tobacco, tea, coffee, cacao, oil palms and many more species were uprooted from their native climes and transported across land and sea, bolstering the economies of colonial powers as they went. Colonialists, the people they’d enslaved and the livestock they transported spread diseases, causing unimaginable death among Indigenous populations — and the plants they took and traded did the same. The historian Alfred Crosby called this process “ecological imperialism.”

Phytophthora and other plant diseases have hitched a ride on these transportations, in soils, on leaves and in the flesh of plants themselves. The strain of P. infestans that triggered the Great Irish Famine came across the Atlantic, hidden aboard a ship of infected tubers heading for Belgium, like Dracula in a box of dirt. Scientists recently discovered that after it had swept Europe it followed British colonial trade routes to East Africa, China and eventually Australia and New Zealand. 

The prolonged travel times of ships up until the 20th century helped prevent the transfer of all but the hardiest diseases. But now plants are moving around the world at an unprecedented rate, and plant diseases are swarming with them. Maritime transport, which accounts for 90% of all global trade, is faster than ever, and carries more than ever. Crops and timber, whole trees and shrubs, cut flowers — all of it uprooted and taken to new lands. The U.S. alone imported $2.5 billion worth of plants in 2020. Plant diseases have even been discovered on the International Space Station.

Phytosanitary regulations are in operation at borders around the world, but they are only effective at preventing what we know about. Many of the Phytophthora currently wreaking havoc around the world had not been discovered until they started causing devastation. Effectively unknown by science, they could not have been stopped or even detected wherever they entered new territory. In September 2021, Phytophthora pluvialis — a pathogen never before detected in Europe — was found infecting trees in rural England. 

“We are constantly throwing pathogens — and I mean constantly, every day, hundreds of thousands — from one biogeographic region into another one,” Jung told me. “Many of them will never find a host there. But some do.” The ones that do usually thrive because the climatic conditions are favorable to their survival and there is a large population of susceptible hosts for them to infect. This might be a native forest, but more often, plant diseases end up thriving and mutating in large manmade agricultural or forestry plantations of mostly identical species. 

Crowds of any one thing promote the spread of pests and diseases. And the dense way we have come to grow identical plants has been a scourge for centuries. The failure of Europe’s potatoes in the 1840s was largely the result of intensive farming of a very narrow range of potato species that, it transpired, were susceptible to P. infestans. In Ireland, it was the infamous lumper potato.

Farming has transformed since then — post-WWII industrial agriculture is a thoroughly scientific domain, teeming with pesticides, herbicides, fungicides, resistance breeding and genetic modification. But the monoculture approach of growing vulnerable fields of identical crops still dominates industrial agriculture, and industrial agriculture dominates agriculture — 1% of the world’s farm owners control 70% of the world’s farmland. 

“Progress and Doom are two sides of the same medal,” wrote Hannah Arendt, and much like the antibiotic paradox, pesticides, herbicides and fungicides have created their own worst enemies. New chemicals are created to kill unwanted organisms, but the targeted organisms over time adapt and survive. It is a cycle that has come to be known as the “chemical dependency treadmill.” For the farmers who can’t afford the chemical weapons, crop losses tend to be unpredictable and devastating. 

The monoculture-like settings of the horticultural nursery trade play a similar role to industrial agriculture. Asymptomatic plant materials arrive in nurseries around the world carrying non-native plant diseases, which they pass on to other plants, which are then redistributed. The same goes for composts that are imported and sold. Cooke and his colleagues launched a project in 2016 called Phyto-threats that aimed in part to establish the amount of Phytophthora present in U.K. nurseries; in one experiment they tested a sample of water from a puddle on the ground in a nursery and found 10 different species of Phytophthora. So many Phytophthora in one place increase the chance of hybridization: new and more virulent species with wider host ranges. Cooke calls them “hopeful monsters.” 

Jung has made similar discoveries. “You buy these little pots with the basil and the coriander from the supermarket, and after a couple days they start looking bad, and they are wilting and they get spots,” he said. “We isolated one: it was carrying the same Phytophthora species that was killing the big beech trees outside: Phytophthora plurivora. So you buy these herbs, they die, you put them on the compost pile and then it spreads onto rhododendrons, then hedge rows and, eventually, it kills the big beech trees a few years later. It’s amazing — the implications are actually really huge.”

What makes a native Phytophthora abandon its companionable habits to carve a path of destruction across the world? The manmade infrastructure of capitalism has created a constant movement of organisms that displaces native pathogens and exposes vulnerable hosts, and fuels a climate crisis that creates new environments in which they can thrive. To maintain the growth of economies, we dismissed the growth of plants. “Endless expansion has unintended consequences,” Tsing said in a 2018 interview. “The new wild,” she called it.

The steep coastal cliffs and expansive beaches of the Waitākere Ranges form one of the most iconic ecosystems in New Zealand, but it’s the ancient and colossal kauri trees that grow on the forested hills that are the area’s most spectacular feature. Kauri trees are some of the oldest in the world; the kauri genus, Agathis, has been around since dinosaurs roamed the Earth. They can grow to be 165 feet tall, with a girth sometimes exceeding 50 feet around, and can live for more than 2,000 years. They are a keystone species — critical to the survival of other plants and animals that live among them — and also form an integral part of Māori mythology. “They are what we call the kaitiaki, or protector of the forest,” Edward Ashby, a board member of the Te Kawerau ā Maki, the tribe (iwi) that is the historic guardian (mana whenua) of the ranges, told me over Zoom. “They are thought of as a living ancestor, a connection between people living now and the atua, or gods of the past.”

The forest started to die in the late 2000s. A survey in 2011 discovered that around 8% of the kauri trees were infected with Phytophthora agathidicida. By 2016, it had shot up to around 20%. “A whole valley in the forest that used to be green and full of birds was now just all these skeletons sticking up,” Ashby said. “It started to look like a graveyard.” He called it “stag horning” — without their leaves, the dead and dying kauri resembled antlers. 

Nobody knows how P. agathidicida arrived in New Zealand, whether it was brought to the country or had been dormant in the soil until climate conditions enabled it to go feral. In a way, it hardly matters how it got there, only that it was bringing 2,000-year-old gods to their knees. “These trees that have lived for essentially the entire human history of New Zealand — some of them are older than all of the tribes,” Ashby said. “Now, seeing them die — what that means for the future is devastating.”

To iwi like Te Kawerau ā Maki, the death of the forest was an existential threat. P. agathidicida, it turned out, isn’t airborne, but waterborne — it was creeping through the soil like a subterranean specter. And of course, it was being aided and abetted by humans: Close to a million people visit the Waitākere Ranges each year, and the disease traveled around the forest primarily on the soles of muddy shoes. Nearly 70% of the dying trees were within 50 meters (164 feet) of walking tracks. 

After consulting with scientists, the iwi made a simple and defiant decision. On Dec. 2, 2017, members of Te Kawerau ā Maki held a ceremony beside a 1,000-year-old kauri tree known as “Aunt Agatha,” in which they laid down a rāhui: a spiritual set of protocols that declares an area to be sacred. Human access to the Waitākere Ranges was thus banned. 

“It’s kind of like a quarantine, a spiritual quarantine,” Ashby said. “It essentially means to commune with the other realm. … In the opinion of the Māori, the environment is a lot older than all of us; it knows how to look after itself. You just need to get out, leave it alone and it will heal. That’s the idea of rāhui.” It was, and remains, one of the biggest and most complex rāhui declared in living memory. 

“When you walk through a mature kauri forest, it’s like walking into a cathedral,” said Lee Hill, a biosecurity specialist and one of a handful of scientists who has been given permission by the iwi to continue entering the forest for research. Unlike in Scotland, there is no chance that such culturally significant kauri trees can be felled, even if they are vectors of infection. So Hill and others have had to get resourceful. They spoke to experts in Australia who had been fighting a similar Phytophthora that was killing jarrah trees. There, they had implemented an unusual approach: They vaccinated their trees. The chemical compound known as phosphite seemed to be a safe biostimulant — it didn’t cure the disease, but it did boost the tree’s immune system and slow the infection. 

It seemed to work for the kauri too. In the last five years, Hill and his team have administered around 17,000 tree vaccinations. “When I go back to these trees four or five years later, they are still there, when they would have been dead,” he said. “But,” he admits, “it’s got this Frankenstein feel to it.” To do the vaccination, first you remove the outer bark on a small patch of the trunk, then drill a hole in the tree trunk and insert a syringe into the hole. A spring on the syringe forces the medicine into the tree. On hot and dry days, the tree will sometimes suck in the liquid itself. 

“It doesn’t look pretty,” Hill said. “You’ve got a god of the forest, then you’ve got me drilling holes in it and injecting it. So, you have to have that conversation with the public or mana whenua, and ask them: Are they okay with this? Having the tool doesn’t always mean we can use it.” A representative from Te Kawerau ā Maki accompanied Hill and his team into the forest and blessed the work as it was being done.

Hill isn’t the only one tackling the disease through cross-cultural collaboration. Monica Gerth, a microbiologist at Victoria University of Wellington, has been studying Phytophthora interactions with plants. Alongside a team of researchers, she used Māori mātauranga (traditional knowledge) of the forest to select and test if four native medicinal plants were able to produce any anti-Phytophthora compounds. They found that roots and extracts from the kānuka plant not only disabled P. agathidicida’s zoospores, it stopped them from germinating. 

“In an ideal world,” Gerth told me, “we’d be able to find something that can be planted near a tree or given to a tree as a medicine, that doesn’t involve trunk injections. They are a good solution for a dying tree. But when you inject a trunk, you damage it, and you need to inject again after four or five years. These kauri can live for thousands of years. Are we going to be injecting them for thousands of years?”

Last year, a few paths on the edge of the forest were reopened, but footwear disinfection points and elevated walkways were installed so that no dirt could be walked in or out. No human feet touched the sacred ground. 

Most of the forest remains closed. It is an act that has forced many New Zealanders to wrestle with questions around their relationship to nature, ones that more of us may have to face in the coming years. Does a forest have value if we are not allowed to look at it — or even go near it? “That question was raised a lot,” said Hill. “If people can’t go in there for five or six years, will they forget its value?” In other words: Do we value nature in and of itself, or just when we are extracting something from it — a resource or pleasurable experience? And what if one of the most promising solutions to our climate crisis is not the endless endeavor of science and technology and perhaps politics, but the eerie stillness of inaction? “In our forest,” Ashby said, “most things have stopped moving.”

Surveillance of the disease goes on in the Waitākere Ranges. “The data has confirmed that the science is aligning with the custom,” Ashby said. “We’re only seeing the disease light up around the edges. … It isn’t showing up in the heart of the forest.” When I asked when the iwi will be lifting the rāhui, he paused. “The environment will tell us when it’s ready, when the mauri [life force] is balanced and the forest is healed,” he said. “Are we seeing more death, or are we seeing new kauri coming through? Are we hearing birds returning? Are we seeing lush green canopy again? There are signs we will look to, and that’s when the rāhui will lift. But ideally, what we would like to see is a sanctuary in the center of the forest: a place that isn’t anything to do with recreation or visitors. A forest just for its own sake, that will be there thousands of years into the future.”

To grieve the death of a tree is to see it as something other than a resource or an object of beauty. It’s something many people struggle with, myself included. It’s easier to grieve the death of an animal. Despite a multitude of forms, animals are essentially like us: Born of flesh and blood, they eat, sleep, talk, procreate, move around and die. 

Plants, by contrast, seem alien in their lifecycles, behaviors and forms. They are alive in a way that is utterly unlike us. Psychologically, we maintain a strange distance between our world and theirs, a sort of denial of the fact that our existence depends on them — a distance that was perhaps required and reinforced so that we could overlook their wholesale destruction for human purposes. Now more than ever, Indigenous knowledge systems with centuries of ecologically grounded thought are reminding us that a dying forest is not a dying resource, but a dying miracle — a miracle that includes and affects us.

During a series of impassioned debates in which Auckland City Council members voted on whether to endorse the rāhui (they eventually did), an elder in the iwi, Te Warena Taua, was asked what it would mean should the disease be allowed to continue without major intervention. He replied with a proverb: “Ko te mauri o te kauri.” It roughly translates to: “If the kauri dies, we die too.”

Potatoes are still farmed in the Andean region of South America where the strain of P. infestans that triggered the Great Irish Famine most likely originated. Wild native potatoes were first domesticated there some 8,000 years ago, and today they are grown in greater diversity than anywhere else in the world. 

In 2002, in the Sacred Valley of the Incas, five different Indigenous Quechua farming communities — around 6,500 people in total — came together to form the Parque de la Papa (Potato Park). Living and growing at an altitude that ranges from 10,000 to almost 16,000 feet above sea level, their farming methods are completely at odds with industrial agriculture. Land ownership is collective, not individual, and the economy is a mixture of monetary and non-monetary, in which barter markets and labor exchange play an important role. Across more than 22,000 acres of mountainous land, they cultivate almost 1,500 varieties of potato — plus beans, barley, quinoa and maize — in a wondrous mosaic of fields. Nature, after all, doesn’t abide by tidy rows.

“Farmers here don’t separate themselves from nature,” said Alejandro Argumedo, who was born to a native Quechua farming family and works as the principal advisor at the Potato Park. “They see themselves as part of this complex and unique system. They maintain their livelihoods and societies in a way that is in harmony with their surroundings. The human community has to work with the wild. … Conservation is a foreign word here, because they have been doing that forever. Agriculture and food production is done in a ritualistic way, in tune with those beliefs.”

Every June, farmers ascend the mountains during some of the coldest nights of the year to observe the Pleiades, a cluster of stars in the constellation Taurus, the brightness of which they believe determines the timing and quantity of rainfall that will come during potato growing season. In 2002, a group of American meteorologists and climatologists investigated the scientific basis for this folk practice and found it to correspond with the presence of certain high, thin and almost undetectable clouds that increase during El Nino years in that area. They concluded that it had a higher forecast accuracy (around 65%) than scientific weather forecasts of the time (55-60%). 

The potatoes come in all colors — brown and yellow of course, but also purple, pink, red, orange and blue — and shapes, from long and curly to stout and knobby. There’s even a black variety, puma maki, that’s shaped like a puma’s claw. The potato is respected, inspirited and treated like family — different varieties are incorporated into marriage proposals, weddings, baptisms and funerals. Humans and potatoes live in companionship. 

Phytophthora infestans has been known since at least the 1500s here — it’s sometimes called “la rancha” in Spanish and “chuyu” in Quechua. But the cultivation of a huge variety of potato species on frequently rotated land plots — as well as the constant crossbreeding with nearby wild potato relatives that have coevolved a natural resistance — has stopped the disease from ever really getting a foothold; there’s never been a need in the park for intensive pesticides or genetic modification beyond crossbreeding. There is a sense that the mountains — some of which are viewed as sacred entities by the Quechua — have dictated the conditions of their society. “Diversity is at the core of farming in a mountain ecosystem,” said Argumedo. “One single variety of potato could never do it here, because every time you move a hundred meters, the eco-climatic conditions change completely.”

Over the last few decades, however, temperatures are rising faster in high mountain areas due to a climate phenomenon known as elevation-dependent warming, and many of the once snow-covered peaks are now bare. As soil and air temperatures rise, greater populations of pests and diseases are hitting the Potato Park — Phytophthora infestans, but also weevils. “Pests and diseases are moving upwards, because their ecological niches are changing,” Argumedo said. “So are plant species.” Farmers have responded to this by moving crops higher too — more than 3,000 feet in the last 30 years.

Upwards and upwards: The farmers, the pests, the plants and the diseases chase each other ever higher. What happens when everyone reaches the top?