Responses of Populus tremula to Picloram and Other Translocated Herbicides

Abstract

Whole aspen plants and isolated aspen root segments were three to ten times more sensitive to the growth‐inhibitory and toxic effects of picloram than to those of 2,4‐D, 2,4,5‐T and dicamba. The activity of picloram in the inhibition of root growth was about ten times higher than that of 2,4‐D and dicamba when tbe substances were added to the nutrient solution. Epinastic responses indicated a very rapid translocation of picioram from the roots to the growing shoot parts. When the herbicides were applied to the mature leaves dicamba rapidly caused a complete inhibition of root growth indicating a rapid translocation of this compound from the leaves to the root tips. Leaf‐applied picloram, 2,4‐D and 2,4,5‐T affected root growth considerably more slowly. Dicamba, 2,4‐D and 2,4,5‐T rapidly killed the directly treated leaf tissue due to high acute toxicity while picloram did not show this type of toxicity. It is concluded that the higher activity of picloram in killing the plant and in inhibition of root and shoot growth can only partly be explained as a result of greater uptake and translocation of this compound.

Killing effect and translocation of picloram in the stem of aspen, Populus tremula

“…ELIASSON (1972) had shown that the root and shoot growth of aspen was very sensitive to picloram at concentrations of lO-'-lO^ "M.…”

“…By short, direct exposure of buds and leaves to the extremely low concentrations affecting cultured cells, we minimized translocation effects (ELIASSON 1972) and could test the sensitivity of different stages to picloram (Fig. 4).…”

“…Most work on herbicides has dealt with application techniques and effect of different concentrations (STERRETT 1969;PEEVY 1960), but factors such as season of application, tree size, type of conductive tissues translocating the herbicide, and tissue damage causing the death of the tree have received only slight attention (ARUONNIER and DELAURAZE 1971;AREND 1967;ELIASSON 1972). The present investigation was conducted to examine these latter factors in aspen using stem application of picloram.…”