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Organic farms can have mixed effects on pesticide use depending on their neighbors

Organic agriculture may be as old as dirt, but that doesn't mean its impacts are fully understood. A team of scientists in the United States and Canada are doing their part to change that.

Researchers at UC Santa Barbara, University of British Columbia, and University of Colorado Boulder discovered that organic farming significantly affects the amount of pesticide used in neighboring fields. The study, published in Science, found that the impact depends on the density and spacing of organic and conventional fields, and clustering organic fields together could provide the most benefits for all farmers.

"We find that organic cropland generally leads to a decrease in pesticide use on nearby organic fields," said lead author Ashley Larsen, an ecologist at UCSB's Bren School of Environmental Science & Management. "In contrast, organic agriculture leads to a small, but significant, increase in pesticide use on nearby conventional fields." The authors suspect that the different responses reflect different reliance on natural pest control methods, although they admit the mechanisms are difficult to test with their data.
There's been a push to increase organic production in the U.S., which begs the question of how this will affect pests and pest control for other farms. Most pesticide studies have focused on the field level, Larsen said, comparing metrics like biodiversity, soil health, and pesticide use between organic and conventional fields. However, agricultural pests and their predators move beyond field boundaries. So, the group sought to understand these interactions between fields, which they call "spillover effects."

Precisely why this is the case is unclear but, the researcherrs said, it may have to do with how the pest-control measures taken by organic farms affect the larger ecosystem. "Organic fields leverage the benefits of natural enemies that reduce the number of pests on their fields, like birds and bugs that eat smaller problematic pests," said co-author Claire Powers, a former graduate student at Bren now pursuing her doctorate at CU Boulder. These predators and pests then venture into neighboring fields for shelter and food.

Organic farmers can benefit from a greater abundance or persistence of their pests' natural enemies, which can be harmed by chemical pesticides in conventional fields. Thus, organic farmers could benefit from clustering together.

On the other hand, an influx of insects from organic fields could drive up the use of chemical pesticides in conventional fields since these fields have smaller, less effective populations of those beneficial species.


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