Effects of Wetting Agent, Stage of Growth, and Species on the Selectivity of Diclofop

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Abstract
A 2-yr field study was conducted to determine whether the addition of wetting agents to diclofop {2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid} could enhance its postemergence control of grass weeds without altering its crop tolerance. In each year, 12 species were treated at two stages of growth with at least two concentrations of diclofop. Regardless of the treatment, selectivity was not altered on wheat (Triticum aestivum L.), soybeans [Glycine max (L.) Merr.], cucumber (Cucumis sativus L.), or sorghum [Sorghum bicolor (L.) Moench]. The addition of wetting agent to diclofop was of no value on highly susceptible grass weed species such as barnyardgrass [Echinochloa crus-galli (L.) Beauv.] or on the more resistant species such as large crabgrass [Digitaria sanguinalis (L.) Scop.]. Only on an intermediately susceptible species such as giant foxtail (Setaria faberi Herrm.) could any significant differences in control be attributed to a wetting agent. The stage of growth of the grass weed species at time of treatment and the diclofop concentration were more important than the presence of a nonionic wetting agent.