Absorption and Penetration of Picloram and 2,4,5-T into Detached Live Oak Leaves

Abstract

Detached live oak (Quercus virginianaMill.) leaves were immersed in aqueous solutions of 4-amino-3,5,6-trichloropicolinic acid (picloram) or (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) for periods up to 4 hr. Herbicide concentration ranged from 10−3to 10−6M; solutions were adjusted to either pH 4, 6, 7, or 8. Absorption of picloram in the presence of equimolar concentrations of 2,4,5-T exceeded that noted for picloram alone. The presence of picloram in the treating solutions had no effect on absorption of 2,4,5-T. This technique allows evaluation of absorption and penetration characteristics of mixtures of herbicides, solvents, and adjuvants.

Uptake of Picloram by Eucalypt Leaf Discs

“…Nobel (1970) found a logarithmic correlation between the pK of some organic acids and their light stimulated uptake, in the presence of potassium, into pea leaf fragments. Baur et al (1971) obtained improved uptake of 2,4,5-T and picloram at lower pH values, but considered 2,4,5-T to be more dependent on the degree of dissociation than picloram . Sargent and Blackman (1970a) This is supported by their observation (Sargent and Blackman 1970b) that penetration, in the light, of young bean leaves by chloride ions is increased as pH falls:…”

“…Better absorption of 3,5-dinitro-o-cresol ), 2,4-D (Hansen and Buchholtz 1952, Weintraub et al 1954, Hauser 1955, Orgell and Weintraub 1957, Wedding and Erickson 1957, Sargent and Blackman 1962, 2,4,5-T (Baur et al 1971), dalapon (Sargent et al 1969a), and picloram Blackman 1970a, Baur et al 1971) has been registered at lower pH values. At least part of the reason for this may be that the presence of the undissociated more lipophilic molecule is favoured by lower pH, and this penetrates more easily than the anion (Crafts 1957, Baur et al 1971). Simon and Beevers (1952) acknowledged that the effect of pH on the degree of dissociation of weak acids played a major role in biological activity, but considered that the ions were also effective .…”

A review of foliar absorption and translocation of 2,4‐D and 2,4,5‐T

“…The differences were not very marked for beans. Baur et al (1971) measured the absorption from a solution of the potassium salt of 2,4,5-T by detached leaves of live oak (Quercus virginiana). They found that absorption was high-est from solutions of pH 4, but not significantly difTerent at pH 6, 7 or 8.…”

“…The interactions between 2,4,5-T ethyl hexyl ester and picloram have been examined by Davis et al (1968b). Picloram was shown to reduce the uptake of 2,4,5-T in mesquite plants although the uptake of picloram was enhanced by the presence of 2,4,5-T. Baur et al (1971) examined the absorption of equimolar mixtures of 2,4,5-T and picloram, both formulated as the potassium salt, by live oak leaves (Quercus virginiana) and found that absorption of picloram was greater when applied with 2,4,5-T than alone, but 2,4,5-T absorption was not afTected by the presence of picloram. However, earlier work by Baur et al (1969) demonstrated that greater quantities of 2,4,5-T were recovered from live oak plants one month after spraying with 2,4,5-T as the 2ethylhexyl ester and picloram than with 2,4,5-T alone.…”

The development of Pisum sativum explant systems for studies concerning source‐sink activities

“…Explant systems (excised shoot, leaf or leaf-disc) have been used in studies of photosynthesis (Atkins andCanvin 1971, Barden et al 1980), herbicidal uptake (Baur et al 1971. Kirkwood et al 1972) and sugar translocation (Schneider 1973) among others.…”