The application of 2.2 kg/ha of picloram provided adequate control of Euphorbia esula L. for 3–5 yr after the treatment year. However, regardless of whether the chemical was applied in 1965, 1966, or 1967, it became ineffective by 1971. While it appeared that the chemical disappeared during the 12-mo period prior to the summer of 1971, this could not be related to the movement of the herbicide by precipitation. Control of E. esula when picloram was applied alone was as effective as when a similar rate of picloram was included in mixtures with B2O3 and 2,4-D.