What makes an organically grown strawberry environmentally friendly?

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Strawberries are a particularly pest prone crop.

To control these pests, more than 9.5 million pounds of pesticides, including over 3 million pounds of methyl bromide, a toxic ozone-depleting chemical is applied each year. Methyl bromide is also associated with an increased risk of prostate cancer in farm workers.

We all like strawberries, but this pesticide use seems excessive: more pounds of pesticides were applied to 28,000 acres of strawberries than to 780,000 acres of cotton (and cotton is one of the world’s most pesticide intensive crops).

To avoid contributing to the use of methyl bromide, I have long purchased locally grown, certified organic strawberries. The organic approach is to rotate strawberries with other crops such as broccoli or a cover crop. Although yields in organic strawberries are only 65% to 89% that of conventional production, organic strawberries sell for 50% to 100% more than conventional berries, so the organic grower still does quite well.

Problem solved? Not so says an article in yesterday’s New York Times.

It turns out that even certified organic strawberries are fumigated with chemicals, including methyl bromide, at the early stages of their lifecycle.

“Before they begin bearing fruit, virtually all plants — whether they will go on to produce conventional berries or organic ones — are treated with fumigants and other synthetic pesticides.” In 2011, more than a million pounds of methyl bromide was applied around the world to young strawberry plants grown in nurseries. Most of the world’s nursery plants are produced here in California.

Why is this practice acceptable to organic growers?

The NYT reports that many organic strawberry growers say that using organic stock amounts to taking a big financial risk with little chance of reward. “You bring sick plants from the nursery, I mean, you might as well keep your money in the bank,” said Carlos Vasquez, who grows 24 acres of organic strawberries in Monterey for Driscoll Strawberry Associates, the largest berry distributor in the world.

Some growers may not know that they are purchasing fumigated stock; others growers don’t see it as a big issue anyway.

“Once the plants bear fruit, they are not treated with synthetic chemicals, so the berries themselves can logically be considered pesticide-free.”

But if you follow this line of argument, then many conventionally grown strawberries can also be considered pesticide-free. Methyl bromide is a soil fumigant and is not sprayed on the fruit. There is no evidence that methyl bromide or any of the other very low levels of pesticide residues on conventionally grown produce cause harm to human health. These residues are usually well below the tolerance levels set by the United States Environmental Protection Agency. In other words, most pesticides sprayed on crops are not harmful to consumers.

Many consumers therefore may conclude that if they are not harmed and their children are not harmed by a particular pesticide, then the application is acceptable. But most farmers and environmentalists would disagree. The toxicity of the pesticide does matter. That is because when it comes to methyl bromide and most other pesticides, farm worker safety and environmental health are key concerns. For this reason, an important goal of sustainable agriculture is to reduce the use of the most toxic substances.

Where do we go from here? Clearly new and improved methods of disease control are needed for organic and conventional growers of strawberries. This includes development of alternative, less toxic compounds that can control serious diseases such as Verticillium wilt. This disease is especially destructive in semi-arid areas where soils are irrigated such as the farmlands of California. Another approach is the development of genetically engineered strawberries with robust resistance to soil-borne pathogens. Because organic farmers are prohibited from growing genetically engineered crops, they would not be able to use such new varieties if they were ever to become available. But they may still be able to use methyl bromide.

Follow Pamela Ronald:
Pamela Ronald is Professor of Plant Pathology at the University of California, Davis, where she studies the role that genes play in a plant’s response to its environment. Her research focuses on the genetics of rice. With her husband, she co-wrote Tomorrow's Table: Organic Farming, Genetics and the Future of Food. She writes a blog of the same name.