Journal of Agricultural Science; Vol. 15, No. 11; 2023 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 1 Effect of Class Act NG Adjuvant on Glyphosate Efficacy in Corn Nader Soltani 1 , Christian A. Willemse 1 & Peter H. Sikkema 1 1 Department of Plant Agriculture, University of Guelph Ridgetown Campus, ON, Canada Correspondence: Nader Soltani, Department of Plant Agriculture, University of Guelph Ridgetown Campus, 120 Main St. East, Ridgetown, ON, N0P 2C0, Canada. E-mail: soltanin@uoguelph.ca Received: August 9, 2023 Accepted: September 5, 2023 Online Published: October 15, 2023 doi:10.5539/jas.v15n11p1 URL: https://doi.org/10.5539/jas.v15n11p1 Abstract There is little information on the effect of the co-application of glyphosate with Class Act NG adjuvant on weed control efficacy and corn yield under Ontario environmental conditions. This study consisted of 6 field experiments that were conducted in Ontario during 2021 and 2022 to determine if the addition of Class Act NG (2.5% v/v) to glyphosate at 450, 900 and 1350 g ae ha -1 would improve weed control and result in a concomitant increase in corn yield. The co-application of glyphosate with Class Act NG resulted in no visible corn injury at 1 and 4 weeks after herbicide application (WAA). The addition of Class Act NG to glyphosate at 450 g ae ha -1 improved control of common lambsquarters, velvetleaf, Powell amaranth, common ragweed, and barnyardgrass as much as 20, 14, 9, 8, and 7%, respectively but there was no improvement in control of giant foxtail, or green foxtail and there was no increase in corn yield. The addition of Class Act NG to glyphosate at 900 g ae ha -1 improved common lambsquarters control 6 and 5% at 4 and 8 WAA, respectively and improved barnyardgrass control 4% at 4 WAA. The addition of Class Act NG to glyphosate at 1350 g ae ha -1 provided no improvement in control of velvetleaf, Powell amaranth, common ragweed, common lambsquarters, barnyardgrass, giant foxtail, or green foxtail and there was no increase in corn yield. Based on this data the co-application of glyphosate with Class Act NG results in improved control of some annual broadleaf and grass weeds (common lambsquarters, velvetleaf, Powell amaranth, common ragweed and barnyardgrass) when glyphosate is applied at 450 or 900 g ae ha -1 ; however, when glyphosate is applied at 1350 g ae ha -1 there was no improvement in weed control. The addition of Class Act NG to glyphosate at 450, 900 and 1350 g ae ha -1 did not result in an increase in corn yield. Keywords: barnyardgrass, common lambsquarters, common ragweed, giant foxtail, green foxtails, Powell amaranth, velvetleaf 1. Introduction Corn (Zea mays L.) is one of the most valuable and dominant grain crops in the world that is grown for human and animal food, biofuel, and other industrial uses (Baker, 2018). Ontario is the main corn-producing province in Canada. Most of the corn produced in Ontario is used for animal feed (60%) and the remainder is used for various industrial uses (40%) (OMAFRA, 2023a). Ontario farmers seed approximately 820,000 hectares of grain corn with a farm-gate value of approximately $1.6 billion annually (OMAFRA, 2023b; Soltani et al., 2022). Weed interference can reduce corn yield dramatically; consequently, effective weed management programs are essential for profitable corn production. A meta-analysis by the Weed Science Society of America (WSSA) determined that corn producers in North America would lose 50% of their production (148 million tonnes) with a value of US$26.7 billion if no weed management tactics are implemented (Soltani et al., 2016a). Despite the rapid evolution of glyphosate-resistant (GR) weeds from the repeated use of glyphosate in GR crops, many crop producers continue to depend on glyphosate as a major component of their weed management programs due to its excellent weed control efficacy, wide margin of crop safety, no residues affecting future crops in the rotation, low environmental impact, and low cost (Beckie et al., 2014; Sikkema & Soltani, 2007). Currently, more than 95% of the corn in Ontario is seeded GR hybrids (Beckie et al., 2014). Glyphosate provides effective, broad-spectrum control of annual, biennial, and perennial grass and broadleaf weeds. However, there has been variable weed control; one reason for the variable control is attributed to the quality of water used for the herbicide carrier (Pratt et al., 2003; Thelen et al., 1995). Some studies have concluded that the inclusion of additives such as ammonium sulfate (AMS) could help improve the weed control