INFLUENCE OF ETHEPHON ON ABSORPTION AND TRANSLOCATION OF HERBICIDES IN CANADA THISTLE

Abstract

The influence of ethephon (2-chloroethylphosphonic acid) on the foliar absorption of 14C-labelled dicamba (3,6-dichloro-o-anisic acid) and 14C-labelled 2,4-D [(2,4-dichlorophenoxy) acetic acid] at three growth stages of Canada thistle (Cirsium arvense (L.) Scop.) was investigated in the growth room. There was increased leaf uptake and retention of dicamba and 14C from 2,4-D under the influence of ethephon at all growth stages; this was reflected in total foliar absorption. The most efficient dicamba/ethephon combination, on the basis of the amount of herbicide accumulated in the roots, was simultaneous ethephon treatment at the bloom and post full bloom stages. Maximum accumulation of 14C from 2,4-D in roots occurred with simultaneous 2,4-D and ethephon application at the post full bloom stage. Differences between acropetal and basipetal accumulation following dicamba treatments were much smaller than those observed after treatment with 2,4-D. More 14C from 2,4-D was accumulated in the roots than was translocated acropetally in all 2,4-D treatments at all growth stages.