Picloram movement from a Chaparral Watershed

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Abstract
After a brush control treatment of soil‐applied pellets of picloram (9.3 lb acid equivalent per acre) on a 2.1‐acre side slope of a 46‐acre chaparral watershed in central Arizona, picloram was detected in the stream water at a gaging station at the outlet of the watershed. Maximum measured concentrations (350–370 ppb) occurred during the first 3 months after treatment and were associated with heavy rainfall. After 14 months and 40 inches of accumulated rainfall, picloram was no longer detected in the stream water. An estimated 4.5% of the picloram applied was lost to stream water. Direct use of stream water from the outlet of the treated watershed when picloram levels were 46–370 ppb could have damaged sensitive crops such as cotton.