The absorption, translocation, and metabolism of14C-picloram and14C-2,4-D applied alone and together to leafy spurge was evaluated. Leafy spurge absorbed 34 and 24% of the14C-2,4-D applied alone and with picloram, respectively, and 14 and 10% of the14C-picloram applied alone and with 2,4-D, respectively. More14C-2,4-D was translocated in leafy spurge than14C-picloram, and adding picloram to14C-2,4-D decreased14C translocation to the roots. Adding 2,4-D to14C-picloram increased the percentage of absorbed14C that translocated in leafy spurge from 28 to 48%. Generally,14C-picloram and14C-2,4-D remained as the parent acid in leafy spurge whether applied alone or together. Of14C-picloram recovered from the roots, 83% was unmetabolized picloram when applied alone compared to 95% when applied with 2,4-D, which probably is the reason for increased leafy spurge control when these herbicides are applied together.

Relative humidity after application, spray additives, and solution pH affected both foliar absorption and translocation of14C-picloram to leafy spurge roots.14C-picloram absorption increased from 11 to 34% and translocation increased from 5 to 21% as time at posttreatment humidity increased from 0 to 48 h. Absorption and translocation were not different when pre- or posttreatment temperatures were 30/18 or 18/10 C (day/night).14C-picloram absorption and translocation to the roots were 18 and 6%, respectively, when applied alone, and increased to 46 and 12%, respectively, when applied with ammonium sulfate at 2.5 kg/ha. Absorption and translocation were unaffected by ammonium nitrate. Foliar absorption and translocation of14C-picloram in leafy spurge were unaffected by pH of unbuffered spray solution but increased at least 50% when applied in a solution buffered at pH 4.8 with trisodium citrate. Foliar absorption in detached leafy spurge leaves increased from 26 to 51% of applied14C as the citrate buffer concentration increased from 0.01 to 0.1 mM, respectively.