An investigation into what sickened several farmworkers in an Idaho hop field earlier this year has closed without a conclusive answer.
The Idaho Statesman reported Wednesday state agriculture investigators determined a fungicide applied on a nearby onion field might have been the cause, but they were unable to prove it.
The workers in Parma fell ill over Memorial Day weekend.
Investigators say many reported being exposed to the spray applied by a crop duster on the field across the street.
Officials were not able to confirm the exposure and some of the workers’ symptoms did not match the fungicide the plane sprayed.
The state’s pesticide compliance manager has issued a regulatory letter to the crop-duster pilot. The letter requires a response covering plans for how to prevent similar incidents.