Environment and Spray Additive Effects on Picloram Absorption and Translocation in Leafy Spurge (Euphorbia esula)

Abstract

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.

Fluroxypyr Absorption and Translocation in Leafy Spurge (Euphorbia esula)

“…Ab-sorption of 14 C-picloram averaged 13% compared to 48 and 36% with 14 C-fluroxypyr or 14 C-2,4-D respectively. These results are similar to previous research with 14 C-2,4-D and 14 C-picloram absorption in leafy spurge (13).…”

“…In general, 14 C-fluroxypyr absorption was similar for plants placed in high humidity immediately after treatment or following 6 to 24 hours at low humidity, but translocation to roots declined as time at low humidity increased. Then results are similar to 14 C-picloram absorption and translocation in leafy spurge which increased as tune at high humidity after treatment increased from 0 to 48 hours (13). However, in that study 14 C-picloram accumulated in the shoot more than the root as time at high humidity increased compared to 14 C-fluroxypyr which tended to increase in the below treated led and root sections as posttreatment time at high humidity increased.…”

Effect of Temperature on Picloram Absorption and Translocation in Leafy Spurge (Euphorbia esula)

“…For example, 2,4-D applied with 14 C-picloram increased the amount of unmetabolized picloram reaching the root by less than 1% of applied 14 C but resulted in 20 to 30% increase in longterm control in the field (9). Picloram absorption and translocation were similar in treatments at 18 or 30º C in previous research (11). However, in that study, herbicide was applied immediately before the temperature change.…”

“…Environmental conditions, especially relative humidity and air temperature, may affect picloram efficacy on leafy spurge. Absorption and translocation of 14 C-picloram was increased when it was applied at high (90 to 95%) compared to low (20 to 30%) relative humidity and when the humidity remained high at least 24 hours after treatment (11). However, absorption and translocation were similar when leafy spurge was preconditioned at high or low temperatures (30/18º or 18/10º C day/night) for 48 hours prior to treatment and was not influenced by posttreatment temperature.…”

Cost-Effective Long-Term Leafy Spurge (Euphorbia esula) Control with Herbicides

“…The reasons for the occasional failure are not known. Picloram absorption is decreased by cool temperature and low humidity (11), but air temperature was 22 C with 42% relative humidity when the treatment was applied in 1986. Also, the plants were in the true-flower growth stage so treatment conditions should have been favorable.…”