Benefit of Adding Ammonium Sulfate or Additional Glyphosate to Glyphosate in Corn and Soybean

Benefit of Adding Ammonium Sulfate or Additional Glyphosate to Glyphosate in Corn and Soybean

Nader Soltani1, Robert E. Nurse2, Christy Shropshire1, Peter H. Sikkema1

1 University of Guelph Ridgetown Campus, Ridgetown, Canada 2 Agricuture and Agri-Food Canada, Harrow, Canada

Abstract Nine field trials (4 in corn and 5 in soybean) were conducted over 2 years (2014 and 2015) to determine if there is greater benefit of adding ammonium sulfate (AMS) (2.5 L∙ha−1 ) or an equal dollar value of glyphosate (406 g∙ae∙ha−1 ) to glyphosate applied at 450, 675 or 900 g∙ae∙ha−1 for weed control in corn and soybean. Glyphosate applied at 450 g∙ae∙ha−1 controlled velvetleaf 90% to 98%, common ragweed 80% - 97%, common lambsquarters 91% - 99%, Eastern black nightshade 83% - 100% and barnyardgrass 73% - 97% in corn and common ragweed 37% - 89%, common lambsquarters 39% - 98%, barnyardgrass 90% - 98% and green foxtail 91% - 98% in soybean. The addition of AMS to glyphosate applied at 450, 675 or 900 g∙ae∙ha−1 provided little to no added benefit for the control of velvetleaf, common ragweed, common lambsquarters, Eastern black nightshade, barnyardgrass and green foxtail in corn and soybean. There was a greater benefit in weed control efficacy by simply adding and equal dollar value of glyphosate (406 g∙ae∙ha−1 ) than AMS (2.5 L∙ha−1 ) to glyphosate. There was no difference in corn or soybean yield among the herbicide treatments evaluated. Based on these results, addition of AMS to glyphosate at rates evaluated had little benefit on weed control efficacy or yield of corn and soybean. Keywords Abutilon theophrasti, Ambrosia artemisiifolia, Corn (Zea mays), Chenopodium album, Echinochloa crus-galli, Efficacy, Glyphosate, Setaria viridis, Soybean (Glycine max), Yield 1. Introduction The Ontario corn and soybean industry covers about 2,000,000 ha, and has annual

farm-gate value of approximately $3.3 billion [1]. Development of management strategies for the control of weeds in corn and soybean has been voted as the number one research priority by the Ontario Weed Committee (the voting members of the Ontario Weed Committee are representatives of the commodity groups such as corn, soybean, wheat and edible beans, industry personnel and public research scientists). Losses due to weeds include reduced yield, decreased quality, reduced field efficiency, and greater losses due to spoilage, increased dockage at the point of sale, and potential rejection of the crop. Currently, more than 90% of the corn and 79% of soybean produced in Ontario are seeded to glyphosate-resistant hybrids/cultivars [2]. Glyphosate-resistant corn and soybean provide Ontario crop producers cost-effective weed management options that are efficacious and environmental friendly [3]. The net economic benefit to farmers is the main reason for wide adoption of this technology by crop producers in eastern Canada [4]. Despite glyphosate broad spectrum weed control, inconsistencies in control of some weed species have been reported at some locations which have been associated with water carrier solution [5] [6]. Nurse et al. [7] has shown benefit of adding AMS to glyphosate at low dose (225 g∙ha−1 ) shortly after application (7 DAA) for control of velvetleaf (Abutilon theophrasti Medic.), however, at the same time there were no benefit for control of common lambsquarters (Chenopdium album L.), redroot pigweed (Amaranthus retroflexus L.), and annual grasses such as foxtails (Setaria spp.). It has been proposed that in the presence of AMS, the sulfate ion, 2 SO4 − binds with Ca2+ to form CaSO4 and prevents formation of a Ca-salt of glyphosate, which is poorly absorbed by the leaves [6]. Instead NH4 + binds with the glyphosate molecule which results in greater absorption of glyphosate into the leaves and therefore improves weed control [6]. Limited information exists on the effect of ammonium sulfate added to glyphosate in corn and soybean under Ontario environmental conditions which can lead to unnecessary expenditures. The objectives of this research were to determine the benefit of adding ammonium sulfate or an equal dollar value of glyphosate (406 g∙ae∙ha−1 ) to glyphosate applied at 450, 675 or 900 g∙ae∙ha-1 for weed control in corn and soybean. 2. Materials and Methods Four field trials (1 at Harrow in 2014 and 3 at Ridgetown in 2015) in corn and 5 field trials in soybean (1 at Harrow in 2014, 1 at Exeter in 2014 and 3 at Ridgetown in 2015) were conducted at the Agriculture and Agri-Food Canada Research Station, Harrow, Ontario, Huron Research Station, Exeter, Ontario and University of Guelph, Ridgetown Campus, Ridgetown, Ontario. The soil ranged from sandy loam to clay loam with 30% to 83% sand, 5% to 36% silt, and 13% to 33% clay, with 2.6% to 5.6% organic matter content and pH 6.0 to 7.4. Seedbed preparation included fall mouldboard plowing followed by two passes with a field cultivator with rolling basket harrows in the spring. Studies were established as a randomized complete block design with four replica-

tions. Treatments for corn and soybean trials were the same and are listed in Tables 1-9. Weed-free control was maintained weed-free by hand hoeing as needed. Each plot was 3 m wide and 8 or 10 m long and consisted of four rows of glyphosate resistant corn/soybean spaced 0.75 m apart. Corn was planted at a rate of approximately 75,000 seeds∙ha−1 in May of each year. Soybean was planted at a rate of approximately 370,000 seeds∙ha−1 in May to early June of each year. Herbicide treatments were applied using a CO2-pressurized backpack sprayer calibrated to deliver 200 L∙ha−1 aqueous solution at 240 kPa. The boom was 1.5 m wide with four ULD120-02 nozzles (Hypro, New Brighton, MN, USA) spaced 0.5 m apart. The herbicides were applied postemergence when weeds were approximately 10 cm in height which corresponded to the V2-4 stage for corn and V2-3 stage for soybean. Weed control was visually estimated on a scale of 0 (no control) to 100% (complete control) at 1, 2, 3, 4 and 8 weeks after herbicide application (WAT). Weed density (soybean only) and dry weight (soybean only) by species were evaluated 4 WAT by counting and cutting plants at the soil surface form 1 square meter in each plot. Plants were dried at 60 C to constant moisture and then weighed. Corn or soybean was harvested at maturity with a small plot combine, weight and moisture recorded and yields were adjusted to 15.5% and 13% seed moisture content for corn and soybean, respectively. Data were analyzed using PROC GLIMMIX in Statistical Analysis Systems Software

Table 1. Percent visible control of velvetleaf 1, 2, 3, 4 and 8 WAT in corn with various rates of glyphosate alone or with AMS or additional glyphosate equivalent to the cost of the AMS at Ridgetown ON (2014-2015)a .

Treatment Rate 1 WAT 2 WAT 3 WAT 4 WAT 8 WAT g∙ae∙ha−1 % Weedy check 0 0 0 0 0 Weed-free check 100 a 100 a 100 100 100 Glyphosate 450 90 d 97 c 98 98 98 Glyphosate + AMS 450 + 2.5 L∙ha−1 93 cd 98 bc 99 98 98 Glyphosate 956 97 bcd 99 ab 99 100 100 Glyphosate 675 96 bcd 99 bc 99 98 99 Glyphosate + AMS 675 + 2.5 L∙ha−1 98 abc 99 ab 99 98 98 Glyphosate 1181 99 ab 100 a 99 100 100 Glyphosate 900 98 abc 100 a 99 100 100 Glyphosate + AMS 900 + 2.5 L∙ha−1 99 ab 100 a 99 98 98 Glyphosate 1406 99 ab 100 a 99 99 99 a Abbreviations: AMS, ammonium sulfate; WAT, weeks after herbicide application. Means followed by the same letter within a column are not significantly different according to Fisher’s Protected LSD at P < 0.05.