Responses of Populus tremula to Picloram and Other Translocated Herbicides

Abstract

AbstractWhole 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.