Influence of late emerging weeds in glyphosate-resistant corn

Abstract

Fifteen field trials were conducted from 2009 to 2011 in Ontario, Canada and Michigan, USA to determine how long glyphosate-resistant corn needs to be kept weed-free after emergence to prevent yield loss. Data were separated into two environments based on when yield loss first occurred after glyphosate application. In Environment 1 (4/15 sites) yield was not reduced when corn was kept weed-free until the 4-leaf stage. However, in Environment 2 (11/15 sites) there was no yield loss when corn was kept weed-free up to the 2-leaf stage. The most prominent weeds were velvetleaf, redroot pigweed, common ragweed, common lambsquarters and foxtail species. While later emerging weeds did not necessarily impact corn yield, weeds emerging after the 2-and 4-leaf corn stage likely produced seed that was added to the soil seed bank. Weeds emerging after 6-, 8-, and 10-leaf corn growth stages were small (low biomass/seedlings) and most likely did not reach reproductive maturity. Based on this research, corn must be maintained weed-free up to the 4-leaf stage. Any weeds emerging after that did not influence corn yield.

The effect of hard water, spray solution storage time, and ammonium sulfate on glyphosate efficacy and yield of glyphosate-resistant corn

“…Season-long control of velvetleaf, a mixture of smooth and redroot pigweed referred to hereafter as pigweed species, common ragweed, common lambsquarters, and large crabgrass was estimated by collecting weed population density and above-ground weed biomass data 8 WAT. Research has shown that weeds emerging after the fourleaf stage of corn do not influence yields; furthermore, weeds emerging after the six-leaf stage are not likely to reach reproductive maturity (Soltani et al 2013). Weed population density and above-ground biomass data were obtained by counting the weeds present in two half-meter quadrats and then the weeds were cut at the soil surface, dried, and weighed.…”

“…For pigweed species, common ragweed, common lambsquarters and large crabgrass, glyphosate reduced above-ground biomass by 96, 99, 94, and 62%, respectively compared with the untreated control (Table 2). Soltani et al (2013) reported that glyphosate applied to corn at the eight-leaf stage caused similar levels of biomass reductions for velvetleaf, redroot pigweed, common ragweed, and common lambsquarters 6 WAT and rated the control of these species at this timing as 100%.…”

“…Since their introduction in 2001, glyphosate-resistant corn hybrids now account for over 90% of corn hectares in eastern Canada, the predominant Canadian corn-growing region (Soltani et al 2013). Within the glyphosateresistant corn production system, glyphosate provides broad spectrum activity, low crop phytotoxicity, low cost of weed control, and greater yields.…”

Tolerance of Corn (<i>Zea mays</i> L.) to Early and Late Glyphosate Applications

“…However, in Environ2, corn yield was not impacted by glyphosate dose or timing. In the literature, reference [7] reported no injury or subsequent yield loss when corn was treated at the 10-leaf stage with 900 g•ae•ha −1 of glyphosate. However, in Ontario, a single application of glyphosate at or after the 8-leaf stage risks yield loss due to early-season competition with weeds [15] and is not recommended [9].…”

“…Currently, glyphosate-resistant hybrids have become adopted widely in North America since their introduction. For example, over 90% of hectares planted in Eastern Canada, the predominant Canadian corn growing region, are glyphosate-resistant hybrids [7]. In the USA, herbicide-resistant corn, glyphosate resistance the predominant weed management trait, accounted for 85% of corn acreage by 2013 [8].…”