Organic farms trigger more pesticide use on nearby conventional farms

Organic farmers dedicate their working lives to producing food with minimal help from pesticides, but in curbing the use of chemicals on their own land, they may unwittingly be triggering a spike in pesticide use over their neighbour’s fence.

Ashley Larsen at the University of California, Santa Barbara, and her colleagues assessed land-use and pesticide data across 14,000 fields in Kern County, California. This is one of the largest crop-growing counties in the state, with produce including almonds, grapes, carrots and pistachios.

The team found that when organic farmland is surrounded by conventional agriculture, the neighbouring farmers seem to increase their pesticide use, with a 10 per cent rise in organic cropland being linked to a 0.3 per cent increase in total pesticide use on conventional fields. Most of this is driven by increased use of insecticides, the researchers found.

This may be because more insects – pests or otherwise – tend to be present on organic land and “spill over” into neighbouring conventional farmland, prompting these farmers to increase their pesticide use. “Pests arrive and seed a new outbreak, and they [farmers] increase pesticide use,” Larsen told reporters during a press briefing. The effect appears to be strongest when neighbouring fields are within 2.5 kilometres of the organic “focal field”.

Conversely, the researchers noted that the presence of organic farmland is linked to a reduction in pesticide use on neighbouring organic fields, with a 10 per cent increase in the area of surrounding organic cropland being associated with a 3 per cent decrease in total pesticide use on organic focal fields. This may be because the larger area of organic farmland allows for a bigger and more stable community of beneficial insects.

Organic agriculture only covers about 2 per cent of farmland globally, but in Kern County, about 5.5 per cent of the agricultural area is organic.

When organic agriculture makes up a high proportion of farmland – perhaps 20 per cent or more – net pesticide use decreases regardless of where the organic fields are sited, say the researchers.

But when relatively small areas of organic farmland – such as in Kern County – are evenly dispersed through the landscape, net pesticide use may in fact be higher than when no organic farmland is present.

“Our simulations suggest that at low levels of organic agriculture in the landscape, we can actually see an increase in net insecticide use,” said Larsen.

However, this impact can be entirely mitigated by clustering organic farmland together to minimise potential pest spillover, she said. “It might be worth considering, at the policy level, how to incentivise spatial clustering of new organic fields to basically leverage the pest control benefits of organic and limit any potential costs of organic on conventional growers.”

This could include subsidy payments for farmers to convert more of their land in certain areas to organic practices, or even the creation of buffer zones between organic and non-organic land.

Robert Finger at ETH Zurich in Switzerland says the findings demonstrate the need for policy-makers to consider land-use policy at the “landscape scale” to maximise the environmental benefits of organic farming. “Fundamentally, just thinking about single fields or single farms is not enough,” he says.