Antagonistic Effects of Desmedipham on Diclofop Activity

The methyl ester of diclofop [2-(4-(2,4-dichlorophenoxy) phenoxy) propionic acid] was used in all of a series of experiments. When it was applied postemergence, it selectively controlled barnyardgrass [ Echinochloa crus-galli (L.) Beauv.] in sugarbeets ( Beta vulgaris L. ‘USH 9′). Tank-mixing diclofop with desmedipham [ethyl m -hydroxycarbanilate carbanilate (ester)] resulted in decreased control of barnyardgrass under greenhouse and field conditions. Losses in activity ranged from 10 to 80%. Delaying application of desmedipham following application of diclofop by 4 days in the greenhouse or in the field resulted in no reduction in barnyardgrass control. Increased rates of diclofop offset the antagonistic effect of desmedipham. Similar losses in activity occurred when Hoe-29152 {methyl-2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoate} was tank-mixed with desmedipham.