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Maybe the Problem Isn’t Just Monsanto & Roundup

Posted by Richard Conniff on February 5, 2014

I wrote an article earlier this week for Yale Environment 360 about the disappearance of pollinators and other beneficial insects.  It quoted University of Kansas entomologist Chip Taylor’s estimate that monarch butterflies have lost 167 million acres of essential milkweed habitat just since 1996.

No coincidence, that’s when Monsanto introduced Roundup-ready crops.  Their tolerance to herbicides made it possible to significantly increase the spraying of weedkillers.  (The increase since 1996 amounts to 527 million pounds of herbicide in the United States.) The resulting loss of milkweed has been a major factor in the near-disappearance of the Monarch migration.

But a new study suggests that it might not be Monsanto alone that is killing off the monarchs.  The study doesn’t absolve Monsanto.  It just adds other elements of agricultural intensification as contributing factors.  (I checked and the research doesn’t appear to have been paid for by Monsanto.  The authors list their funding sources as Pennsylvania State University College of Agricultural Sciences and the US Environmental Protection Agency.)

Here’s the press release:

The increasing use of chemical herbicides is often blamed for the declining plant biodiversity in farms. However, other factors beyond herbicide exposure may be more important to species diversity, according to Penn State researchers.

If herbicides are a key factor in the declining diversity, then thriving species would be more tolerant to widely used herbicides than rare or declining species, according to J. Franklin Egan,research ecologist, USDA-Agricultural Research Service.

“Many ecotoxicology studies have tested the response of various wild plant species to low dose herbicide exposures, but it is difficult to put these findings in context,” said Egan. “Our approach was to compare the herbicide tolerances of plant species that are common and plant species that are rare in an intensively farmed region. We found that rare and common plant species had roughly similar tolerances to three commonly used herbicides.”

This could mean that herbicides may not have a persistent effect in shaping plant communities.

The researchers, who report their findings in the online version of the journal Environmental Toxicology and Chemistry, said that over the past several decades, in the same time that the use of herbicides was on the rise, other factors such as the simplification of crop rotations, segregation of crop and livestock and increasing mechanization have also been rapidly evolving. In addition, the clearing of woodlots, hedgerows, pastures and wetlands to make way for bigger fields has continued apace and resulted in habitat loss.

While the findings are preliminary, the approach could be effective in clarifying the implications of herbicide pollution for plant conservation, Egan said.

“These findings are not an invitation to use herbicides recklessly,” he said. “There are many good reasons to reduce agriculture’s reliance on chemical weed control. But, for the objective of plant species conservation, other strategies like preserving farmland habitats including woodlots, pastures and riparian buffers may be more effective than trying to reduce herbicide use.”

Egan worked with David Mortensen, professor of weed and applied plant ecology, and Ian Graham, an undergraduate student in plant science.

Journal Reference:

  1. J. Franklin Egan, Ian M. Graham, David A. Mortensen. A comparison of the herbicide tolerances of rare and common plants in an agricultural landscape. Environmental Toxicology and Chemistry, 2014; DOI: 10.1002/etc.2491

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