The Basis of the Antagonistic Effect of 2,4-D on Diclofop-Methyl Toxicity to Wild Oat (Avena fatua)

Abstract

The interaction between diclofop-methyl {2-[4-(2,4-dichlorophenoxy)phenoxy] methyl propanoate} and 2,4-D [(2,4-dichlorophenoxy)acetic acid] was evaluated. Foliar applications of the two herbicides in a tank mixture were antagonistic with respect to wild oat (Avena fatuaL.) control. Application of mixtures of the two herbicides to wild oat roots resulted in an additive herbicidal effect. The acid form of 2,4-D was determined to be the component of the 2,4-D formulation that reduced the toxicity of foliar-applied diclofop-methyl to wild oat. Analysis of diclofop-methyl solutions with and without added 2,4-D revealed no degradation products of dichlofop-methyl, nor any evidence of complexing between diclofop-methyl and 2,4-D. Addition of 2,4-D to the diclofop-methyl spray solution did not affect diclofop-methyl spray retention by, or penetration into, wild oat leaves. Movement of radioactivity to roots and to shoot apices following application of14C-diclofop-methyl to wild oat leaves was reduced by addition of 2,4-D to the treatment solution. Deesterification of diclofop-methyl was inhibited by 2,4-D. The accumulation of diclofop-methyl in these wild oat leaves resulted in membrane damage and leaf necrosis. Symplastic movement of the des-methyl acid, diclofop, to sensitive meristematic areas was reduced. As insufficient toxicant reached meristematic areas to permanently interrupt meristematic activity, the wild oat plants were able to outgrow the contact damage to their leaves.

Enhanced herbicide metabolism induced by 2,4‐D in herbicide susceptible Lolium rigidum provides protection against diclofop‐methyl

“…It is known that ACCase herbicide efficacy is reduced by 2,4‐D (and MCPA) in Avena fatua and other grass species, and various mechanisms have been proposed including recovery from membrane depolarisation, reduction in herbicide uptake or translocation and altered herbicide metabolism including reduced diclofop‐methyl de‐esterification . Here, we demonstrate that 2,4‐D induced protection against diclofop‐methyl in susceptible L. rigidum is not caused by altered herbicide uptake or translocation.…”

Determination of Antagonism between Cyhalofop-butyl and Other Rice (Oryza sativa) Herbicides in Barnyardgrass (Echinochloa crus-galli)

“…LSD a represents the difference within a herbicide treatment across harvest times, and LSD b represents the difference across herbicide treatments within a harvest time. hydrolysis of diclofop-methyl to the herbicidally active acid metabolite, which ultimately led to reduced movement to the meristematic site of action (22). Triclopyr, which has a similar mode of action to 2,4-D in susceptible species, did not appear to alter uptake or metabolism of CB within 18 HAA.…”

Selectivity of diclofop‐methyl between wheat and wild oat: growth and herbicide metabolism

“…Wheat probably would still be resistant even if the active herbicide was translocated to the site of action, since it can rapidly metabolize the herbicide to nonphytotoxic forms. Todd and Stobbe (1976) proposed that selectivity was due to differences in the deestedfication rate of diclofop-methyl to diclofop, analogous to that of benzoylprop-ethyl (Beynon et al 1974, Hill et al 1978. Deestedfication of benzoylprop-ethyl to benzoylprop appears to activate the compound.…”