2017 ASHS Annual Conference

Since 2005, the Oregon Department of Environmental Quality has worked with the Walla Walla Basin Watershed Council to monitor pesticide water quality in the Walla Walla Basin through the Pesticide Stewardship Program. Initial investigations centered on waterways traversing the fruit orchards of the Milton Freewater area. Between 2005-2008, only the 12 most toxic pesticides to salmonoid life were monitored. Since 2009, the number of pesticides analyzed increased from 12 to over 120 and the number of pesticide detections increased significantly. OSU Extension Service helped growers adopt best management practices that would help reduce contamination of the waterways, including: - spray calibration workshops, timing of sprays, wind speeds notifications, sprayer training to spray trees adjacent to the ditches on one side only and ensuring that nozzles were pointing away from the open waterways. Between 2005-2009, the acute water quality standard (wqs) for chlorpyrifos (0.083 µg/L) was often exceeded but the trend was consistently downwards. Since 2010, most detected concentrations were below the acute standard and average concentrations have been close to the chronic wqs (0.041 µg/L). Since 2009, carbaryl has always been detected at levels of less than half the lowest EPA aquatic life benchmark (0.5 µg/L). In 2010/2011, diuron was detected at multiple monitoring sites at levels above EPA aquatic life benchmarks and was associated with the irrigation district, which switched to mechanical controls and softer chemistries. Since 2013, diuron detections have been barely detectable. In recent years, the program was expanded to include streams traversing peas and wheat plantations and to date, only deminimis contamination levels of those waterways have been attributed to pea/wheat growers. Additional best management practices included the introduction of flags on the edges of waterways to help growers determine wind direction so that sprays were only conducted on the side of the waterway on which the wind was blowing away from the stream. Nozzle choice, inclusion of anti-drift products in the spray tank, maximum height of the nozzles set at 10 inches above the ground and avoiding boom bouncing were all recorded digitally by the growers as proof of adoption. Despite expanding the geographic area in the project and increasing the number of pesticide analytes each year, the total number of pesticide detections in 2016 was the lowest in the past five years. The Walla Walla basin remains a success story in reducing pesticide contamination and this has been achieved through voluntary collaboration only.