Influence of Diphenylether Herbicide Application Rate and Timing on Common Waterhemp (Amaranthus rudis) Control in Soybean (Glycine max)1

Abstract

Diphenylether herbicides may be viable options for postemergence (POST) control of common waterhemp in soybean. A 2-yr field research project was conducted to determine whether common waterhemp control is influenced by application timing and rate of acifluorfen, fomesafen, and lactofen. Common waterhemp control was 9, 9, and 8% greater 7, 14, and 21 d after treatment, respectively, after the early postemergence (EPOST) application timing compared with the POST application timing. Lactofen provided greater common waterhemp control than did acifluorfen or fomesafen, and only the highest application of lactofen provided greater than 85% common waterhemp control 21 d after POST application. No significant differences in common waterhemp dry weight were determined among the three rates of acifluorfen, fomesafen, and lactofen applied EPOST. The highest application rates of fomesafen and lactofen reduced common waterhemp dry weight more than did the lowest application rates applied POST. The highest application rate of fomesafen also reduced common waterhemp dry weight more than did the intermediate application rate. Single degree of freedom contrasts indicated that all diphenylether herbicides reduced common waterhemp dry weight more than did imazethapyr.Nomenclature: Acifluorfen; fomesafen; imazethapyr; lactofen; common waterhemp, Amaranthus rudis Sauer #3 AMATA; soybean, Glycine max (L.) Merr.Additional index words: Postemergence, herbicide application rate, herbicide application timing, weed control.Abbreviations: ALS, acetolactate synthase; COC, crop oil concentrate; DAT, days after treatment; EPOST, early postemergence; NIS, nonionic surfactant; POST, postemergence.