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Strawberry growers seek a sustainable path forward without go-to fungicides

Wilted: Pathogens, Chemicals, and the Fragile Future of the Strawberry Industry

Julie Guthman
University of California Press
322 pp.
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How do conventional, corporate berries that have traveled more than 2000 miles compare with local, organic berries? They are certainly more affordable and taste just as good—but at what cost?

In her new book, Wilted, Julie Guthman explores the strawberry industry, from its origins in the mid-1800s to our kitchen tables today. But her focus is not limited to the berries themselves. She also examines the influence of pathogens and chemicals on the human shippers, growers, and workers that underlies the berry industry, all while revealing how planting, tending, and harvesting berries in California can cost a grower more than $60,000 per acre (1).

In the starring role of this story is a common and intransigent pathogen called Verticillium dahliae, or wilt. Playing opposite is a duo of chemicals: methyl bromide—the silver-bullet fungicide—and chloropicrin, also known as tear gas.

Verticillium is a soilborne fungus that transforms vigorous green leaves into dry brown litter. The pathogen can survive dormant in soil for up to years. When triggered to germinate, it moves into plant roots and eventually into vessels that carry water and nutrients to the shoots. In response, a plant may cut off its own water circulation. Eventually, it will wilt and die.

As a soil pathogen, Verticillium is under the influence of the local soil microbiome. If the microbiome is robust, the pathogen may be controlled by other microbes in the system. Conversely, in highly disturbed soils or soils that host the same crop year after year, a lack of diversity may enable the pathogen to run rampant. Unless, that is, the soil is forced into submission. Enter methyl bromide, stage left.

The brominated hydrocarbon has been an industry standard for more than 65 years. When administered in combination with chloropicrin, it essentially sterilizes the soil, killing off bacteria, nematodes, and weeds. But it also seems to boost growth, which makes it even more useful.

Being gaseous and light, methyl bromide quickly wafts from soil into the air, and any left in the soil degrades within a couple of months. (Of the dozens of trace pesticides that land strawberries on the Environmental Working Group’s dirty dozen each year, surprisingly, this is not one of them.)

At the height of its reign, tens of thousands of tons of methyl bromide were used on various U.S. crops. Unfortunately, it not only kills pests, it also destroys ozone.

Several years after the Montreal Protocol agreement banning chlorofluorocarbons was signed in 1987, an amendment that targets other halogenated hydrocarbons, including methyl bromide, was added. It took the strawberry industry nearly three decades to capitulate. For years, the industry applied for, and received, critical-use exemptions. Officially, methyl bromide’s use on strawberry fields ended in 2016 (its application to strawberry rootstock or starts is another story also covered in Guthman’s book).

Often in such stories, there are stand-in chemicals waiting in the wings. They may not be ideal, and some may be more toxic than the compound they are replacing, but they are usually there. In this case, there are no clear alternatives.

Growers can apply chloropicrin on its own, but it is less effective and, because of its toxicity, may require buffer zones to protect human health. Methyl iodide, meanwhile, was pulled from the market under protest over concerns for consumer, worker, and community health before it ever hit the field. There are also a range of nonchemical techniques under exploration, including taking the organic route. None of these alternatives offers an easy out. Organic farming, for example, requires growing smarter, tighter, and more hygienically. It also takes more land in a state where land is costly.

But solutions do not have to be all or none, organic or conventional. The best approach may be some combination: the development of less toxic fumigants combined with the cultivation of helpful soil microbes; steam treatment (killing soilborne organisms with heat) and anaerobic soil disinfestation; breeding disease-resistant plants.

As Guthman writes, “readers should not assume the existence of an optimal pathway. Solutions that are efficacious, reasonably harmless, and economically viable remain elusive.” And she notes that sustainable solutions must be accessible rather
than monopolized.

Wilted provides a detailed case study for a strategy that I imagine could be applied to many other coevolved systems that arose as a result of our post–World War II love affair with chemicals. From antibiotics to pesticides, we are only now realizing the pitfalls of this approach (resistance, toxicity, and systems built on chemicals that are destined to fail, at some point.)

The strawberry industry’s predicament is just one example of how our strategy of dominating ecological systems and focusing on increased output at all cost is short-sighted, with diminishing returns. Recent efforts to work with, rather than against, natural systems suggest a path forward.

1. M. P. Bolda et al., Sample Costs to Produce and Harvest Strawberries (University of California Agriculture and Natural Resources Cooperative Extension and Agricultural Issue Center, UC Davis Department of Agricultural and Resource Economics, 2016).

About the author

The reviewer is at the Ronin Institute, Montclair, NJ 07043, USA, and the author of Natural Defense: Enlisting Bugs and Germs to Protect Our Food and Health (Island Press, 2017).