Science - 16.08.2019

SCIENCE sciencemag.org 16 AUGUST 2019 • VOL 365 ISSUE 6454 647

H

ow do conventional, corporate ber-

ries that have traveled more than

2000 miles compare with local, or-

ganic 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 ber-

ries themselves. She also examines the in-

fluence of pathogens and chemicals on the

human shippers, growers, and workers that

underlies the berry industry, all while reveal-

ing 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 com-

mon and intransigent pathogen called Ve r -

ticillium 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 dor-

mant in soil for 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. Eventu-

ally, 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 dis-

turbed 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 admin-

istered in combination with chlo-

ropicrin, it essentially sterilizes

fields ended in 2016 (its application to straw-

berry 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 toxic-

ity, may require buffer zones to protect hu-

man health. Methyl iodide, meanwhile, was

pulled from the market under protest over

concerns for consumer, worker, and commu-

nity health before it ever hit the field. There

are also a range of nonchemical techniques

under exploration, including taking the or-

ganic 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 com-

bined with the cultivation of helpful soil mi-

crobes; steam treatment (killing soilborne

organisms with heat) and anaer-

obic 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 vi-

able remain elusive.” And she

notes that sustainable solu-

tions 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 des-

tined to fail, at some point.)

The strawberry industry’s predicament is

just one example of how our strategy of dom-

inating 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 sys-

tems suggest a path forward. j

REFERENCES AND NOTES

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).

10.1126/science.aay1461

AGRICULTURAL TOXICOLOGY

By Emily Monosson

Berry blues

Strawberry growers seek

a sustainable path forward

without go-to fungicides

Workers harvest

strawberries in

Carlsbad, California.

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).

Email: [email protected]

Wilted

Julie Guthman

University of California

Press, 2019. 322 pp.

PHOTO: ZUMA PRESS INC/ALAMY STOCK PHOTO

BOOKS et al.

the soil, killing off bacteria, nema-

todes, 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, sur-

prisingly, this is not one of them.)

At the height of its reign, nearly 20,000

tons of methyl bromide were used on vari-

ous 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, includ-

ing 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. Of-

ficially, methyl bromide’s use on

strawberry