Effective weed control in corn (Zea mays L.) is important to optimize yield. Concern over environmental impact of atrazine and selection for glyphosate resistance has increased the need to develop alternative strategies that use herbicides other than atrazine and glyphosate and appropriate cultural practices to control weeds. Research was conducted during 2011 and 2012 to determine weed and corn response to herbicide programs containing dicamba, glufosinate, and glyphosate applied postemergence alone or with atrazine in single- and twin-row planting patterns. Planting pattern had no effect on common ragweed (Ambrosia artemisiifolia L.) and Texas panicum (Panicum texanum L.) population and did not interact with herbicide program. Effective weed control hastened maturity in some but not all instances. Under weed-free conditions, corn grain yield was higher in 5 of 7 trials when planted in twin rows versus single rows at equivalent corn populations (141,000 plants？ha？1). These results suggest that while planting pattern may not impact weed control dramatically, planting corn in twin rows may be an effective alternative to single-row planting patterns because of increased yield under high corn populations. 1. Introduction Effective weed management continues to be important in obtaining optimum corn yields [1]. Common ragweed is among the top ten most common weeds in corn in North Carolina [2]. Other troublesome broadleaf weeds include Palmer amaranth (Amaranthus palmeri S. Wats.), common lambsquarters (Chenopodium album L.), and sicklepod (Senna obtusifolia (L.) Irwin and Barneby) [2]. Texas panicum is considered one of the most troublesome weeds in corn production in the southeast US [3]. Several herbicides control Texas panicum in corn but not always completely [3–5]. Atrazine controls many broadleaf weeds and some grasses in corn and can be applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST) [6, 7]. Although used on many hectares in the US [8], atrazine is no longer used in Europe because of concern of endocrine disruption in amphibians [9]. Residues of atrazine have been found in groundwater and surface water [10] and use of atrazine continues to be reviewed by the EPA in the US [7]. Development of herbicide-resistant biotypes has increased challenges in managing weeds in corn and other agronomic crops [11]. To decrease the likelihood of development of herbicide-resistant biotypes, rotation of herbicide modes of action is essential and should be coupled with cultural practices that minimize reproduction of
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