Common Waterhemp (Amaranthus rudis) Control in Corn (Zea mays) with Single Preemergence and Sequential Applications of Residual Herbicides1

Abstract

Control of common waterhemp in corn with chloroacetamide and dinitroaniline herbicides can be inconsistent. Common waterhemp control by dimethenamid, S-metalochlor, pendimethalin, and three formulations of acetochlor, applied alone or with atrazine as single preemergence (PRE) or sequential PRE followed by postemergence (POST) treatment, was determined. The manufacturer's suggested use rate (1 time) of PRE herbicides was compared with sequential applications (0.66 time PRE followed by 0.34 time POST) of herbicides. POST applications included dicamba to control emerged common waterhemp. Single and sequential herbicide applications controlled common waterhemp at least 98%, 28 d after planting (DAP). But herbicides applied sequentially were more effective than PRE treatments by 56 DAP. Encapsulated acetochlor formulations controlled common waterhemp at least 85% by 56 DAP regardless of application method. Sequential applications of S-metolachlor controlled common waterhemp greater than 83%. Atrazine improved common waterhemp control regardless of herbicide or application method 56 DAP. Sequential applications of dimethenamid or S-metolachlor alone or with atrazine were more effective than single PRE applications of these herbicides.Nomenclature: Acetochlor; atrazine; chloroacetamide; dimethenamid; dinitroaniline; pendimethalin; S-metalochlor; common waterhemp, Amaranthus rudis Sauer #3 AMATA; corn, Zea mays L. ‘Pioneer 34R07’.Additional index words: Chloroacetamide, dinitroaniline, herbicide application timing, sequential applications.Abbreviations: DAP, days after planting; POST, postemergence; PRE, preemergence.