Abstract
The use of glyphosate-resistant corn has facilitated a shift from a reliance on preemergence residual herbicides to postemergence (POST) herbicides, and in some cases exclusively glyphosate. Glyphosate is a non-selective herbicide that is relatively slow-acting, which may allow weeds to continue to compete with corn after application and potentially decrease crop yield. The addition of several POST corn herbicides, with some residual control, to an early-season glyphosate application was examined to determine if the tankmix combination would improve the speed of weed control compared to glyphosate applied alone. Seven field trials were conducted over three years (2009, 2010 and 2011) near Ridgetown and Exeter, Ontario. The control of common ragweed was improved 3 days after application (DAA) with three POST glyphosate tankmixes compared to glyphosate alone. However control was still less than 55%. Depending on the weed species examined, at 28 DAA two of the glyphosate tankmix treatments tested provided better common ragweed, common lambsquarters, or green foxtail control than glyphosate alone. Treatments providing better weed control at 28 DAA also typically decreased weed density compared to glyphosate alone.
Highlights
Since the commercialization of glyphosate-resistant corn (Zea mays L.) in 1998 [1], there has been rapid adoption of this technology
Producers were encouraged to use pre-emergent (PRE) herbicides in conjunction with one or two post-emergent (POST) glyphosate applications to maintain adequate season-long weed control [4], some studies have indicated that yield loss due to crop-weed competition can be avoided if producers eliminate PRE corn herbicides and rely on early POST glyphosate treatments, provided they are applied in a timely fashion [5,6,7,8]
Three field studies were conducted at the Huron Research Station (HRS) (43 ̊19’N, 81 ̊30’W), Exeter, Ontario and four studies were conducted at the University of Guelph, Ridgetown Campus (RC) (42 ̊26’N, 81 ̊53’W), Ridgetown, Ontario from 2009 to 2011
Summary
Since the commercialization of glyphosate-resistant corn (Zea mays L.) in 1998 [1], there has been rapid adoption of this technology. Acceptance of glyphosate-resistant corn and soybean (Glycine max (L.) Merr.) has been rapid because it is relatively economical, has wide margin of crop safety, provides excellent weed control, and can increase crop rotation flexibility since glyphosate has no residual activity. Producers were encouraged to use pre-emergent (PRE) herbicides in conjunction with one or two post-emergent (POST) glyphosate applications to maintain adequate season-long weed control [4], some studies have indicated that yield loss due to crop-weed competition can be avoided if producers eliminate PRE corn herbicides and rely on early POST glyphosate treatments, provided they are applied in a timely fashion [5,6,7,8]. It is recommended that POST herbicides in corn be applied by the V3 to V4 corn stage [9] and no later than 23 days after
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