Chemical Drift

by by Deborah Lehmann

It started with tomatoes. When I arrived at Buckhorn Gardens in early July, the other interns on the three-acre vegetable farm in southwestern Colorado had just finished pulling up almost the entire crop of these juicy summer delicacies. They yanked the plants up by the roots and threw them—flowers, leaves, stems and all—into black garbage bags destined for the landfill.
They did the same thing with the potatoes. And the fava beans. And anything else that exhibited the telltale symptoms: curling, cupping, twisting leaves, and sometimes a hard nub on the stem. By the time I left at the end of August, we had pulled up the peas, the peppers, and the beans too.
This is not what I envisioned when I decided to spend my summer working on an organic farm at the base of the San Juan Mountains. I expected hot days in the field, planting seeds and harvesting cucumbers. I awaited a bounty of succulent produce. I thought I would spend the summer months enjoying the outdoors in a pristine, unpolluted environment.
Instead, I ended up learning a lot about chemicals. Or at least the one chemical that made its way into the Buckhorn fields from an adjacent ranch, affecting nearly all of the crops. I harvested plenty and I planted some, but mostly I got a grim picture of the way we think about our land in this country. With deeds in our hands and barbs on our fences, it’s easy to forget how the actions we take don’t always stay within property lines.

A Chemical Culprit
Breigh Peterson, who started Buckhorn Gardens four years ago at age 27, never would have guessed that her plants would be harmed by an herbicide. Her farm lies on land owned by a cattle ranch in a secluded valley. There are no giant cornfields or orchards right next door, no crop-dusters in the vicinity. And though her farm is not certified organic, Peterson doesn’t use any chemicals at all, organic or synthetic. The closest she gets to a pesticide is dusting some crops with flour and cayenne pepper to deter flea beatles.
So when an extension agent from Colorado State University came out to the farm and told Peterson that her plants’ symptoms looked like signs of chemical residue, she didn’t believe him. She recalled their conversation: “He told me, ‘You know, this actually looks like herbicide.” And I said, ‘No way. There’s no way this could possibly happen here.’”
When the twisted and cupped leaves started showing up in early summer, Peterson thought they were symptoms of a common virus called curly top. But something seemed fishy even from the beginning; curly top usually doesn’t show up so early in the season, and even if it did, it shouldn’t have been spreading this quickly. Six weeks later, when plant tissue samples came back negative for curly top and a slew of other viruses, Peterson started thinking the extension agent was onto something.
It was then that she approached the owners of the ranch and learned that they were spraying an herbicide known as Milestone to control thistle in their pastures. A little computer research confirmed her new hypothesis. “I looked it up online, and the plant pictures looked the same as our plants,” Peterson said. “Exactly the same.”  Thus began weeks of research and questions: were the crops fit for sale? Was the soil fit for planting? Would the ranch reimburse Buckhorn Gardens for damages incurred? We found articles about a number of organic farms that had lost their certification due to pesticide drift and sued for thousands, sometimes millions of dollars. But because Peterson was leasing land from the ranch owners, who wanted an organic farm on the property, a lawsuit was out of the question.
The Dow Chemical Company released Milestone in 2006, adding another player to a thriving market of synthetic weed- and pest-control agents. A search on the Pesticide Action Network’s Pesticide Database turns up 2,412 herbicides registered for use on land. There are thousands of other aquatic herbicides, insecticides, fungicides, algaecides and chemical fertilizers on the list. According to the US Environmental Protection Agency, Americans apply more than one billion tons of pesticides and herbicides each year. The potential for contamination is huge.
According to Dow, Milestone uses “a novel, breakthrough molecule” to control invasive broadleaf weeds such as thistle and knapweed in all sorts of environments, from pastures and wildlife management areas, to campsites and cereal fields. The chemical is generally regarded as a low-risk herbicide; it is even registered under the EPA’s Reduced Risk Pesticide, which signifies that it is safer for humans and for the environment than available alternatives. Its biggest selling point, though, is that it’s selective. Spray Milestone on a weed-infested wheat field, and in a few weeks only the neat rows of wheat will remain.
Milestone kills plants by bombarding them with growth hormones. Peter Heywood, professor of Biology at Brown University, explained that all plants have a hormone called auxin, which regulates development. Aminopyralid, the active ingredient in Milestone, is an auxin mimic, and plants that are flooded with this chemical lose control over cell division, causing leaves to brown, curl, twist, and ultimately, die. So how does the wheat in our Milestone-sprayed field remain undisturbed? Grasses respond differently to auxin, so aminopyralid only affects broadleaf plants. Unfortunately, most of the summer crops on a diversified vegetable farm fall into that category.
The directions on the Milestone label contain intricate instructions for avoiding contamination. Users are required to leave a 50-foot border between the spray area and any non-target broadleaf crops. The label also contains a drift reduction advisory that spans almost an entire page and covers everything from droplet size, to swatch adjustment, to wind, to temperature and humidity. The managers of the ranch adjacent to the Buckhorn fields said they left a 900-foot buffer zone between the spray area and the farm site. They sprayed out of a small tank that rested on the back of a four-wheeler—a tool similar to a hand-sprayer, but not worn on somebody’s back.
“It’s hard for people to believe that this could happen from the way they were spraying,” Peterson said. “The people who spray weeds for the county, both of them think I’m crazy. They’re like, ‘No way this can happen.’”
Maybe the ranchers didn’t follow the directions closely enough. Maybe the wind changed direction or picked up suddenly. Or maybe one of the thousands of other factors out of their control kicked in. Whatever the case, Peterson received a letter in early August with test results from a lab at the University of Montana. Aminopyralid was present in three of the four plants she sent in. The one plant uncontaminated was, ironically, a weed.

Persistence, Persistence
In attempting to solve scientific problems, we tend to get caught up in our innovation and ingenuity. What we’re not so good at is predicting all the unintended consequences of our actions. Assembling a chemical substance that mimics a natural plant hormone and targets specific unwanted crops for destruction is genius. But what do we do when that chemical persists long after we want it or travels to new locations?
Despite its low-risk classification, aminopyralid has been causing a lot of problems over the past several years, and all in all, Buckhorn had it easy. When contamination occurs by air, the herbicide has a half-life of about a month, and it degrades even faster when exposed to water. The Buckhorn Gardens soil was fit for planting by the end of the summer. But contamination can also occur through other channels, and when it does, things get a lot more complicated.
In the summer of 2008, gardeners in the UK started experiencing crop failures in beds they had covered with purchased manure. It turned out that this manure came from animals that had eaten hay sprayed somewhere down the line with aminopyralid-based herbicides. Dow touts the persistence of these herbicides, saying they may control weeds for a whole season with only one application. This is how persistent aminopyralid is: a farmer sprays it on his pasture. Animals eat the contaminated hay and are unharmed. The sprayed hay is digested and comes out the other end. Aminopyralid stays in the manure, and when a nearby farmer uses some of that manure to add nutrients to his soil, the aminopyralid releases slowly as soil bacteria break it down. Plants exposed to the manure don’t germinate. Ones that do are twisted, curled and cupped. The farmer’s soil can stay contaminated and unfit for planting for a year or more.
Guy Barter, the head of horticultural advisory services for the Royal Horticultural Society, told The Guardian during the crisis that he was receiving more than 20 phone calls every week from concerned farmers and gardeners. “It’s happening all over the country,” he told the newspaper. “A lot of cases we are seeing is where people have got manure from stables and the stables have bought their hay from a merchant, and the merchant may have bought hay from many farmers, possibly from different parts of the country.” Aminopyralid wasn’t just leaking out of farmers’ fields, it was traveling large distances through lengthy supply chains. It was difficult to figure out where the chemical came from, and it was just as difficult to predict where it would go next.
More recently, growth-regulator herbicides have hurt small farms here in the United States — in Washington, California, Ohio and North Carolina. Jeanine Davis, an associate professor and extension specialist at North Carolina State University, said farmers in her community began having problems with contaminated manure last year. “Damage was widespread like we’ve never had it before,” she said. One extension agent in the state told Davis that 25 to 30 cases had been reported in his county alone.
Although both Dow and the UK’s Pesticides Safety Directorate have determined that vegetables grown in contaminated manure can be eaten without harmful health effects, aminopyralid is not approved for most food crops, and produce treated with the chemical may not be sold. Farmers who use contaminated manure could lose their crops for up to one year as they wait for the aminopyralid to break down in their soil. Without some form of reimbursement, those financial losses could be devastating to small, diversified operations.
Davis said there is sometimes disagreement at the University about whether to encourage weed-control agents like Milestone. “These herbicides are very effective, and some of our weed scientists promote them because they’re so persistent that they don’t have to be sprayed very often. It appears to be very sustainable from the point of view of the hay farmer.” But Davis said she finds the persistence of the chemical troubling.
Aminopyralid goes “way beyond the person who applies it,” Davis said. “That hay farmer has no control by the time that hay has gone from his field to the compost pile in my garden.”
Herbicides containing aminopyralid were taken off the shelves in the UK for two years following the complaints about tainted manure. This year, they were reintroduced with stringent restrictions—ones that Davis would like to see imposed in the United States. According to the new rules, aminopyralid-based herbicides may only be used on sheep and cattle pastures, and they may not be used on pastures that grow hay. Before purchasing the herbicides, farmers must discuss their plans for use with an adviser affiliated with BASIS, an independent organization that establishes standards for the pesticides within the country. On top of that, they must sign a document stating that they understand the effects of this product on their animals’ manure. Distributors in the UK may only carry the aminopyralid-based weed retardants if they re-train their staff on the use of the chemicals.
Regulation may help keep these chemicals in check. But there are some unintended consequences that will keep causing trouble.
“I hope people realize that if we keep doing this, we’re going to have a huge manure problem on our hands,” Davis said. “I keep telling people that all you need to do is put manure on your garden. It is such a wonderful resource, and to see us ruining that resource just really upsets me.”
Dow’s chemists came up with a tiny auxin-mimicking molecule to kill broadleaf weeds. They might not have known it would devastate small farmers across the globe. Or that it would create a waste problem out of something that was once a closed circle of nutrient recycling. But our scientific track-record shows an impressive knack for innovation, with a deficiency at considering consequences.

Assessing the Damages
Life at Buckhorn was morose for the last weeks of summer. With hardly any summer produce in our fields, we had to cut short our Community Supported Agriculture program. CSA members had signed up in the spring to receive a share of produce each week until November, but at a certain point it became clear that the gardens weren’t going to produce enough vegetables to make it through the season.
The financial implications of the drift incident at Buckhorn were huge. Peterson lost 85 percent of her crop — at least $40,000 dollars worth of damages. That doesn’t take into account the $10,000 the ranch is paying to reimburse CSA members. Or the labor that went into planting those seeds and tending those plants. “From spring until June, we worked 12-, 15-, 16-hour days,” Peterson said. “Everything we planted died.” Even crops that kept producing were stunted. The leeks were smaller than normal. The onions never bulbed. The squash plants produced one-third the amount they usually do.
In my last week at Buckhorn, I seeded beds of arugula, spinach and mustard greens. The good news is that they have all germinated and are growing well — no cupping, curling or twisting to be found. What’s more, the ranch agreed to stop spraying anywhere in the valley. But there are still herbicides in the region. Thirteen miles down the road, the small mountain town of Ridgway is planning to use aminopyralid to meet state regulations on control of invasive weeds. When I talked to Peterson on the phone last week, she had recently voiced her concerns at a town meeting and is advocating alternative methods of weed control, like goat grazing.
It is easy to think of air and water as common resources. Water moves and wind blows, and we can see how something deposited in one place may end up in another quite quickly. What is harder for us to internalize is that land is a common resource too. We may have property rights, but that doesn’t mean that our actions are confined within our fences. And with supply chains as long as they are today, we can never be sure where our inputs will travel. Who knows, they might just end up on someone’s tomato plants.

Deborah Lehmann B’10.5 has a huge manure problem on her hands.