Organic agriculture can increase pesticide use on nearby fields

This is a striking conclusion from a recent study in the journal Science. The researchers used field-level pesticide use and crop data for 14,000 fields over seven years in Kern County, California, alongside US-wide data on organic agriculture and pesticide use.

A team of scientists in the United States and Canada 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 neighbouring fields.

Worrying and unintended effect

The researchers emphasise that with the arrival of new organic fields, and higher levels of insects, conventional farmers often respond by increasing their use of pesticides. This negates the benefit of reducing pesticides in organic fields and the new organic fields can ultimately lead to an increase in pesticide use.

It is a worrying and unintended effect of the increase in organic farming. Consumers and policy makers often see this way of farming as a means to improve agricultural sustainability through more natural production methods, particularly in regards to pesticides and pest control. Although organic production covers less than 2% of global agricultural lands, it has grown from 15 million hectare in 2000 to over 73 million hectare today.

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Spillover impacts

Continental policy initiatives, such as the European Union’s Farm to Fork strategy, as well as regional targets such as the California Air Resource Board scoping plan for achieving carbon neutrality foreshadow a further and more substantial increase in organic production.

Although organic production generally improves environmental conditions such as soil and water quality, these improvements often come with a substantial yield trade off, which makes the overall environmental impact of organic production ambiguous or at least context-dependent.

The researchers say that reducing the environmental footprint of agriculture while maintaining or improving yields is a major challenge of the coming decades. “However, the environmental impacts of organic production practices are only partially understood and it remains unknown whether such production practices have spillover impacts, beneficial or not, for surrounding producers.”

Organic crop production includes a suite of on-farm practices that differ from conventional management techniques. The researchers were interested in the direct and spillover effects of surrounding organic cropland on pesticide use on both organic and conventional crop fields.

The most benefits for all farmers.

They find that surrounding organic agriculture drives a small but significant increase in pesticide use on conventional fields while leading to a larger and also a significant or marginally significant decrease in pesticide use on organic fields, depending on the situation.

“We find that organic cropland generally leads to a decrease in pesticide use on nearby organic fields”, says 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.”

Clustering organic fields together could provide the most benefits for all farmers

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.

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.

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Benefits clustered organic agriculture

According to the study, changing from a baseline of 0% to 5% organic cropland results in an increase in insecticide use to 109% of the baseline, if organic fields are dispersed. At 20% organic cropland, insecticide use decreases to 83% of baseline use.

If organic fields are clustered, however, the same changes would result in 90% and 64% of baseline insecticide use for 5% and 20% organic cropland, respectively. Given that over 7 M kg of insecticide active ingredients were applied in Kern in 2019, the difference between clustered and dispersed organic agriculture therefore represents sizable differences in the amount of insecticides that would be applied annually.

The results indicate that organic fields harbour higher levels of both insect pests and natural enemies, that spill over to affect other fields. Conventional focal fields may realise more of the negative effects, either due to lower treatment thresholds or due to reduced persistence of natural enemies in conventional fields. By contrast, organic fields may realise a benefit of surrounding organic cropland because a landscape of reduced synthetic pesticides may enable more effective control by natural enemies.

The researchers explain that surrounding organic cropland primarily influences insect pest control. Decades of research suggest that insect pests and natural enemies are influenced by local and landscape composition and configuration.

Reducing pesticide use

Insecticides are the most widely used types of pesticide in California’s high-value agriculture and herbicides are rarely used for organic fields in this system. Although local and landscape features, including surrounding organic fields, influence weeds and herbicide use in other systems, it is not wholly surprising that little effect is observed here.

Clustering organic fields could reduce pesticide use on both organic and conventional fields. Focusing on organic fields, the researchers find that the influence of surrounding organic fields is greatest for fields within 0.5 km of the focal field, which are primarily immediately adjacent fields or other crops in multi-crop fields.

The large local benefit of clustering may help explain why organic fields tend to be part of larger farms and are much more commonly multi-cropped fields. However, there remains a benefit of surrounding organic agriculture at distances between 1 to 2.5 km from an organic field for some pesticides, suggesting there is also a landscape-level effect of organic agriculture on net pests and pest control.

As farmers and policy makers consider how to increase organic production, leveraging the pest control benefits of clustered organic production might be an important consideration. It may generate more viable organic and conventional agriculture with less environmental pollution stemming from pesticide use.

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Organic targets

The benefit of clustering remains sizeable even if organic agriculture reaches 25% of cropland. Thus, it may be valuable to incentivise local clustering of organic fields to reduce pesticide use on both organic and conventional farms, regardless of organic targets.

The results suggest that efforts to increase organic cropland could lead to a decrease in pesticide use, but that is more likely at higher levels of organic cropland in the landscape. At low levels of organic cropland, the opposite is expected. Spatially clustering organic fields and spatially separating organic and conventional fields could reduce the environmental footprint of both organic and conventional croplands.