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The pilot of this crop duster lays down a mist of spray while making a pass over a field in this 2014 file photo.

Controversy has again soured relations between local growers and environmental-justice activists, this time over concerns related to a three-county study of pesticides' effects on rural air quality.

Central Valley agricultural officials have accused activist groups of planning to skew the research by sending individuals equipped with air-monitoring equipment into areas being treated with harmful chemicals.