Evaluation of Application Program and Timing in Herbicide-Resistant Corn

Field studies were conducted from 2007 to 2009 in East Lansing, MI to evaluate three residual herbicide programs, three POST herbicide application timings, and two POST herbicides in glyphosate- and glufosinate-resistant corn. Herbicide programs included a residual PRE-applied herbicide followed by (fb) POST application (residual fb POST), a residual herbicide tank-mixed with a POST herbicide (residual + POST), and a nonresidual POST. Three POST herbicide application timings included early POST (EP), mid-POST (MP), and late POST (LP) at an average corn growth stage of V3/V4, V4/V5, and V5/V6, respectively. The two POST herbicides evaluated were glyphosate and glufosinate. Control of common lambsquarters and giant foxtail was evaluated 28 d after the LP application. Glyphosate often provided greater weed control than glufosinate. The LP application resulted in greater giant foxtail control compared with the EP application timing, which may be attributed to control of late-emerging weeds. The EP application timing improved common lambsquarters control compared with the LP application timing. The residual + POST program resulted in greater weed control compared with the residual fb POST program in all years. The effect of residual herbicide program, POST herbicide, and POST application timing on corn grain yield varied by year. In 2007, the use of glyphosate resulted in higher grain yield compared with glufosinate. In 2008, corn grain yield was the highest in the PRE fb POST program and with POST applications at EP and MP. To provide the most consistent weed control and minimize the likelihood of grain yield reductions, a PRE fb POST program applied at EP or MP is recommended.Nomenclature: Acetochlor; atrazine; glufosinate; glyphosate; common lambsquarters, Chenopodium album L.; giant foxtail, Setaria faberi Herrm; corn, Zea mays L.