Publication Summary

Forest practices, including the use of pesticides, are conducted in accordance with Best Management Practices (BMPs) established in the Washington Forest Practices Rules and Regulations. This project was undertaken to evaluate BMP effectiveness through intensive field monitoring of forest pesticide applications. Determination of BMP effectiveness is based on interpretation of various provisions of state water quality standards, forest practice rules, pesticide registration labels issued by the U.S. Environmental Protection Agency, and Department of Agriculture pesticide regulations.

Forest practices, including the use of pesticides, are conducted in accordance with Best Management Practices (BMPs) established in the Washington Forest Practices Rules and Regulations. This project was undertaken to evaluate BMP effectiveness through intensive field monitoring of forest pesticide applications. Determination of BMP effectiveness is based on interpretation of various provisions of state water quality standards, forest practice rules, pesticide registration labels issued by the U.S. Environmental Protection Agency, and Department of Agriculture pesticide regulations.

The study employed intensive sampling of streams that flow through or adjacent to units treated by aerial (helicopter) applications of forest pesticides to monitor the entry of chemicals into surface waters. Seven of these case studies served as representative examples of BMP implementation, and were used to determine BMP effectiveness for the application scenarios represented. We sampled dormant and early foliar herbicide operations conducted during April and May, late foliar herbicide sprays conducted in September, and an insecticide/fungicide spray conducted in early June of 1991. The silvicultural operations included five conifer release herbicide sprays (one dormant spray, two early foliar sprays, and two late foliar sprays), one site preparation herbicide spray (late foliar), and one Christmas tree pest control spray. Pesticides applied included 2,4-D, triclopyr, glyphosate, imazapyr, metasystox-R, and chlorothalonil.

Pesticides were detected in streams following applications at all seven sites, with peak levels ranging from 0.02 to 7.55 mg/L. Pesticides were also detected in runoff at the four sites where runoff events were sampled. Runoff sampling occurred 2 to 25 days following the applications, and concentrations ranged from 0.17 to 2.49 mg/L. Maximum instantaneous concentrations found were 1.29, 2.49, 7.55, 1.15, 1.72, and 2.80 mg/L, respectively, for triclopyr, 2,4-D, glyphosate, imazapyr, chlorothalonil, and metasystox. Excluding runoff events, peak concentrations occurred within the first three hours following the spray in all cases. Maximum 24-hour average levels were 0.13, 0.69, 0.56, 0.36, 0.18, and 3.25 mg/L, respectively, for the same six pesticides. Based on the timing of peak concentrations, the majority of pesticide introduction to streams was attributed to off-target swath displacement and drift from spray areas near streams. The overall distribution of pesticide levels indicated that overspray of small headwater streams (which the applicator had incorrectly assessed as not having surface flow) also contributed to levels found at some sites.

The BMPs were determined to be partially effective or ineffective based on three tests of effectiveness. First, water quality standards regarding toxic levels of pesticides were not met in at least one of the case studies. Second, the BMPs were not effective at avoiding drift causing direct entry of pesticides into surface waters or Riparian Management Zones, as required by the Forest Practice Rules. And third, the BMPs were not effective at complying with certain pesticide product label restrictions regarding entry to surface waters and avoidance of off-target drift. Recommendations for improving the BMPs include revised stream buffer requirements, specifications for spray nozzle configurations, and improved procedures for determining whether small streams must be buffered. Recommendations for stream buffers include minimum buffers of 15 to 25 meters for downwind applications and 75 to 90 meters for upwind applications along all flowing streams.