Effect of ammonium sulfate and water hardness on glyphosate and glufosinate activity in corn

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1 Effect of ammonium sulfate and water hardness on glyphosate and glufosinate activity in corn Nader Soltani 1, Robert E. Nurse 2, Darren E. Robinson 1, and Peter H. Sikkema 1 1 University of Guelph Ridgetown Campus, Ridgetown, Ontario, Canada N0P 2C0; and 2 Agricuture and Agri-Food Canada, Harrow, Ontario, Canada N0R 1G0 ( nsoltani@ridgetownc.uoguelph.ca). Received 15 March 2011, accepted 23 July Soltani, N., Nurse, R. E., Robinson, R. E. and Sikkema, P. H Effect of ammonium sulfate and water hardness on glyphosate and glufosinate activity in corn. Can. J. Plant Sci. 91: Eight field trials were conducted over a 3-yr period (2008 to 2010) near Harrow and Ridgetown, Ontario, to evaluate the effect of water hardness (distilled: 0 ppm; intermediate: 353 ppm; and very hard 1799 ppm) on full label doses of glyphosate (900 g a.e. ha 1 ) and glufosinate (400 g a.i. ha 1 ) [with and without ammonium sulfate (AMS) at 2.5 L ha 1 ] efficacy in corn. There was no effect of water hardness on control of velvetleaf (ABUTH), redroot pigweed (AMARE), common lambsquarters (CHEAL), and annual grasses green foxtail (SETVI) and barnyardgrass (ECHCG) when glyphosate was applied with or without the AMS. There was also no difference in yield of corn with various water sources when glyphosate was applied with or without AMS. Glyphosate applied with various water sources with or without AMS controlled ABUTH, AMARE, CHEAL, and annual grasses better than glufosinate with or without AMS. Glufosinate with AMS, especially at the 1799 ppm water hardness, generally controlled ABUTH, AMARE, and CHEAL better than glufosinate without AMS, but there was no improvement in annual grass control. indicated an 11% increase in yield when glufosinate was applied with AMS compared with when applied without AMS. Based on these results water hardness and AMS had little benefit on the efficacy of glyphosate in corn; however, efficacy of glufosinate was improved when applied with AMS at high water hardness. Key words: Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, corn (Zea mays), Chenopodium album, Echinochloa crus-galli, efficacy, glufosinate, glyphosate, Setaria viridis, yield Soltani, N., Nurse, R. E., Robinson, R. E. et Sikkema, P. H Incidence du sulfate d ammonium et de la dureté de l eau l efficacite du glyphosate dans les cultures de maïs. Can. J. Plant Sci. 91: De 2008 à 2010, les auteurs ont effectue huit essais au champ pre` s de Harrow et de Ridgetown, en Ontario, en vue d e tablir quels effets la durete de l eau (eau distille e : 0 ppm; durete moyenne : 353 ppm; eau très dure : ppm) aurait sur l efficacite de la dose recommande e sur l e tiquette de glyphosate (900 g de matie` re active par hectare) et de glufosinate (400 g de matie` re active par hectare) [avec et sans sulfate d ammonium (AMS) a` raison de 2,5 L par hectare] quand on l applique au maı s. La durete de l eau n a aucune incidence sur la lutte contre l abutilon (ABUTH), l amarante réfle chie (AMARE), le che nopode blanc (CHEAL) ainsi que la se taire verte (SETVI) et le pied-de-coq (ECHCG), deux gramine es annuelles, quand on applique le glyphosate avec ou sans AMS. Le rendement du maı s ne varie pas davantage avec les divers types d eau quand on utilise le glyphosate avec ou sans AMS. L application de glyphosate avec divers types d eau, avec ou sans AMS, permet de mieux combatte ABUTH, AMARE, CHEAL et les gramine es annuelles que le glufosinate avec ou sans AMS. En ge néral, le glufosinate combat mieux ABUTH, AMARE et CHEAL avec que sans AMS, surtout quand l eau est tre` s dure (1799 ppm), mais la lutte contre les gramine es annuelles ne s en trouve pas ame liorée. L application de glufosinate avec de l AMS augmente le rendement de 11 %, comparativement a` l application de glufosinate sans AMS. Compte tenu de ces résultats, on estime que la durete de l eau et l AMS pre sentent peu d inte reˆt pour l application de glyphosate au maı s. Ne anmoins, l addition d AMS accroıˆt l efficacite du glufosinate quand l eau est tre` s dure. Mots clés: Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, maïs (Zea mays), Chenopodium album, Echinochloa crus-galli, efficacité, glufosinate, glyphosate, Setaria viridis, rendement Corn (Zea mays L.) production is important to the agricultural economy of Canada. Most of the corn produced in Canada is grown in Ontario. In 2009, corn growers produced nearly 6.4 million tonnes on approximately ha with a farm gate value of more than $1 billion (McGee 2011). Currently, more than threequarters of the corn produced in Ontario is glufosinate or glyphosate-resistant. Glufosinate and glyphosateresistant corn provide Ontario crop producers efficacious, cost-effective weed management options that do not result in unacceptable risks to the environment (Sikkema and Soltani 2005). The rapid and widespread adoption of this technology by corn producers in eastern Canada strongly suggests a net economic benefit to farmers (Beckie et al. 2006). Glyphosate and glufosinate provide broad spectrum weed control, but inconsistent control of some species has been reported at some Abbreviations: AMS, ammonium sulfate; WAA, weeks after application Can. J. Plant Sci. (2011) 91: doi: /cjps

2 1054 CANADIAN JOURNAL OF PLANT SCIENCE Table 1. Analysis of water sources used in eight field trials conducted in Ontario, Canada, during z Ions Distilled water Intermediate water Hard water Magnesium (ppm) Calcium (ppm) Sodium (ppm) Zinc (ppm) Manganese (ppm) Copper (ppm) Iron (ppm) Boron (ppm) Total hardness (ppm) z Water samples were analyzed for composition at Agri-Food Laboratories, Unit1, 503 Imperial Road North, Guelph, ON, Canada N1H 6T9. locations and has been associated with carrier water solution (Pratt et al. 2003). There are reports that performance of glyphosate is reduced with hard water that contains certain cations (Nalewaja and Matysiak 1992; Hall et al. 2000; Bailey et al. 2002; Pratt et al. 2003; Bernards 2005a, b; Nurse et al. 2008). Water that contains greater than 500 ppm of Ca and /or Mg is generally considered hard water (Pratt et al. 2003). The complexes formed between glyphosate and cations in hard water cause formation of salts that are not absorbed as readily as free glyphosate, resulting in reduced efficacy (Thelen et al. 1995; Hall et al. 2000; Hartzler 2010). Little information on the role of hard water in glufosinate efficacy has been published (Pratt et al. 2003). Glufosinate has a molecular structure similar to that of glyphosate, and is believed to react similarly with cations in hard water (Pline et al. 1999). More research is needed, especially at the manufacturers recommended doses to evaluate the influence of water hardness on glufosinate and glyphosate efficacy for the control of troublesome weeds in Ontario. The addition of ammonium sulfate (AMS) to the carrier solution of glyphosate or glufosinate reduces hard water cation antagonism and can enhance control of certain weed species at certain doses (Thelen et al. 1995; Pratt et al. 2003; Nurse et al. 2008). In the presence of AMS, the sulfate ion, SO 4 binds with Ca to form CaSO 4 and prevents formation of a Ca-salt of glyphosate, which is poorly absorbed by the leaves (Thelen et al. 1995). Instead NH 4 binds with the glyphosate molecule that results in greater absorption of glyphosate into the leaves and therefore improves weed control (Thelen et al. 1995). Nurse et al. (2008) found greater benefit at low Table 2. Percent weed control for glyphosate (900 g a.e. ha 1 ) and glufosinate (400 g a.i. ha 1 ) with and without ammonium sulfate (AMS; 2.5 L ha 1 ) at various water hardness 2 WAA in eight field trials conducted in Ontario, Canada, during (data pooled)z Percent weed control Untreated Glyphosate 0 95ab 99a 91abc 93ab Glyphosate ab 99a 95a 92abc Glyphosate abc 99a 91abc 92abc Glufosinate 0 84d 95b 88bc 89cd Glufosinate d 93b 89bc 89cd Glufosinate d 94b 86c 89cd GlyphosateAMS 0 96a 99a 97a 94a GlyphosateAMS ab 98a 96a 92abc GlyphosateAMS ab 99a 95a 93ab GlufosinateAMS 0 89c 94b 93ab 90bcd GlufosinateAMS bc 94b 92abc 90bcd GlufosinateAMS bc 93b 93ab 88d Weed-Free Glyphosate (no AMS) vs. glyphosate (with AMS) NS (94 vs. 95) NS (99 vs. 99) NS (92 vs. 96) NS (92 vs. 93) P P P P Glufosinate (no AMS) vs. glufosinate (with AMS) *(83 vs. 90) NS (94 vs. 94) *(88 vs. 93) NS (89 vs. 89) P P P P Glyphosate vs. glufosinate *(95 vs. 87) *(99 vs. 94) *(94 vs. 90) *(93 vs. 89) P P P P Glyphosate (no AMS) vs. Glufosinate (no AMS) *(94 vs. 83) *(99 vs. 94) *(92 vs. 88) *(92 vs. 89) P P P P Glyphosate (AMS) vs. glufosinate (AMS) NS (95 vs. 90) *(99 vs. 94) *(96 vs. 93) *(93 vs. 89) P P P P ad Means followed by the same letter within a column are not significantly different according to Fisher s Protected LSD at PB0.05.

3 SOLTANI ET AL. * WATER HARDNESS ON GLYPHOSATE AND GLUFOSINATE 1055 doses of glyphosate (225 g ha 1 ) and greater benefit shortly after application (7 d after application). Weed control was species specific, resulting in greater control of velvetleaf (Abutilon theophrasti Medic.) and almost no benefit for redroot pigweed (Amaranthus retroflexus L.), common lambsquarters (Chenopdium album L.) and annual grasses such as foxtails (Setaria spp.) (Nurse et al. 2008). Pratt et al. (2003) compared velvetleaf control using glyphosate (380 g a.e. ha 1 ) or glufosinate (360 g a.i. ha 1 ) with tap water (427 ppm CaCO 3 )or deionized water and found that velvetleaf control was reduced from 56 to 37% with glyphosate and from 33 to 16% with glufosinate when tap water was used. Both studies were only able to show a benefit to the addition of AMS at below label doses of glyphosate and/or glufosinate. Limited information exists on the effect of ammonium sulfate and water hardness on efficacy of labeled doses of glyphosate or glufosinate in corn under Ontario environmental conditions. The objectives of this research were to determine: (a) the relative efficacy of glyphosate and glufosinate in corn across various water hardness levels, and (b) the effect of AMS addition on the efficacy of full labeled doses of glyphosate and glufosinate. MATERIALS AND METHODS Eight field trials were conducted over a 3-yr period at the Agriculture and Agri-Food Canada Research Station, Harrow, Ontario (1 site in 2008, 2009, 2010) and the University of Guelph, Ridgetown Campus, Ridgetown, Ontario (1 site in 2008 and 2 sites in 2009 and 2010). 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 in the spring. The study was established as a randomized complete block design with four replications. Treatments included an untreated control and glyphosate (900 g a.e. ha 1 ) or glufosinate (400 g a.i. ha 1 ) in three different water sources (distilled: 0 ppm; intermediate: 353 ppm; very hard: 1799 ppm water hardness) applied POST alone or with ammonium sulfate (AMS) at 2.5 L ha 1. Treatments also included a weed-free control that was maintained by hand hoeing as required. Each plot was 3 m wide and 8m long and consisted of four rows of glyphosate/glufosinate resistant corn spaced 0.75 m apart. Corn was planted at a rate of approximately seeds ha 1 in May of each year. Table 3. Percent weed control for glyphosate (900 g a.e. ha 1 ) and glufosinate (400 g a.i. ha 1 ) with and without ammonium sulfate (AMS; 2.5 L ha 1 ) at various water hardness 4 WAA in eight field trials conducted in Ontario, Canada, during (data pooled)z Percent weed control Untreated Glyphosate 0 85a 90a 87a 83a Glyphosate a 90a 87a 83a Glyphosate a 87a 83a 81ab Glufosinate 0 56d 77bcd 69cd 71c Glufosinate d 75cd 69cd 69c Glufosinate d 74d 65d 68c GlyphosateAMS 0 83a 88a 86a 79ab GlyphosateAMS a 87a 87a 76b GlyphosateAMS a 88a 86a 77b GlufosinateAMS 0 66b 79b 74b 71c GlufosinateAMS cd 77bcd 71bc 69c GlufosinateAMS bc 78bc 75b 67c Weed-Free Glyphosate (no AMS) vs. glyphosate (with AMS) NS (82 vs. 82) NS (89 vs. 88) NS (86 vs. 86) NS (82 vs. 77) P P P P Glufosinate (no AMS) vs. glufosinate (with AMS) NS (55 vs. 63) NS (75 vs. 78) NS (68 vs. 73) NS (69 vs. 69) P P P P Glyphosate vs. glufosinate *(82 vs. 59) *(88 vs. 77) *(86 vs. 71) *(80 vs. 69) P P P P Glyphosate (no AMS) vs. glufosinate (no AMS) *(82 vs. 55) *(89 vs. 75) *(86 vs. 68) *(82 vs. 69) P P P P Glyphosate (AMS) vs. glufosinate (AMS) *(82 vs. 63) *(88 vs. 78) *(86 vs. 73) *(77 vs. 69) P P P P ad Means followed by the same letter within a column are not significantly different according to Fisher s Protected LSD at PB0.05.

4 1056 CANADIAN JOURNAL OF PLANT SCIENCE The intermediate hard water (353 ppm) was collected from a well near Erin, Ontario, and the very hard water (1799 ppm) was collected from a well at a research farm near Plattsville, Ontario, in Water sources were analyzed for composition (Table 1) at the Agri-Food Laboratories (Unit 1, 503 Imperial Road North, Guelph, ON, N1H 6T9). Total hardness was defined as the sum of the calcium and magnesium concentrations both expressed as equivalents of calcium carbonate in milligrams per liter. Herbicide treatments were applied using aco 2 -pressurized backpack sprayer calibrated to deliver 200 L ha 1 aqueous solution at 240 kpa. The boom was 1.5 m wide with four ULD nozzles (Hypro, New Brighton, MN) spaced 0.5 m apart. The herbicides were applied postemergence at the 4 to 6-leaf stage of the corn when weeds were up to 20 cm tall. Crop injury was rated 2 and 4 wk after application (WAA) and weed control was rated 2, 4 and 8 WAA on a scale of 0 to 100% (0%no injury/control and 100% plant death/complete weed control). At 10 WAA, weed density and biomass (shoot dry weight) from weed populations naturally occurring in each plot was determined by cutting the plants at the soil surface from two 0.25-m 2 quadrats. Weeds were separated by species, combined from the two quadrats in each plot, counted (weed density), and dried in the oven at 608C to a constant moisture and the dry weight was recorded. Yield was measured by harvesting the two middle rows of each plot with a small plot combine when the crop had reached physiological maturity. Yields were adjusted to 15.5% moisture. All data were subjected to analysis of variance (ANOVA). Data were analyzed using the PROC MIXED procedure of the SAS Institute, Inc. (2008). Variances were partitioned into the random effects of location, year, year by location, block within year by location, and their interactions with fixed effects (Treatments). Significance of random effects was tested using a Z-test of the variance estimate, and fixed effects were tested using F-tests. Error assumptions of the variance analyses (random, homogeneous, normal distribution of error) were confirmed using residual plots and the Shapiro-Wilk normality test. To meet the assumptions of the variance analysis, percent injury and weed control data were arcsine square-root transformed when needed. Data were compared on the transformed scale and converted back to original scale for presentation of results. were made to compare (a) the value of adding AMS or no AMS and (b) any difference between glyphosate and glufosinate with and without AMS on Table 4. Percent weed control for glyphosate (900 g a.e. ha 1 ) and glufosinate (400 g a.i. ha 1 ) with and without ammonium sulfate (AMS; 2.5 L ha 1 ) at various water hardness 8 WAA in eight field trials conducted in Ontario, Canada, during (data pooled)z Percent weed control Untreated Glyphosate 0 92a 95a 95a 68ab Glyphosate a 95a 94abc 69a Glyphosate a 94ab 93abcd 68ab Glufosinate 0 68d 89cd 87ef 67abc Glufosinate d 88cd 87ef 66abc Glufosinate d 87d 85f 64abc GlyphosateAMS 0 92a 94ab 95a 67abc GlyphosateAMS a 93b 96a 62c GlyphosateAMS a 95a 95a 62c GlufosinateAMS 0 79b 90c 91cd 64abc GlufosinateAMS bc 88cd 90de 62c GlufosinateAMS c 89cd 91cd 61c Weed-Free Glyphosate (no AMS) vs. glyphosate (with AMS) NS (89 vs. 90) NS (95 vs. 94) NS (94 vs. 95) *(68 vs. 64) P P P P Glufosinate (no AMS) vs. glufosinate (with AMS) NS (68 vs. 76) NS (88 vs. 89) *(86 vs. 91) NS (66 vs. 62) P P P P Glyphosate vs. Glufosinate *(90 vs. 72) *(95 vs. 89) *(95 vs. 89) NS (66 vs. 64) P P P P Glyphosate (no AMS) vs. glufosinate (no AMS) *(89 vs. 76) *(95 vs. 88) *(94 vs. 86) NS (68 vs. 66) P P P P Glyphosate (AMS) vs. glufosinate (AMS) NS (90 vs. 76) *(94 vs. 89) *(95 vs. 91) NS (64 vs. 62) P P P P af Means followed by the same letter within a column are not significantly different according to Fisher s Protected LSD at PB0.05.

5 SOLTANI ET AL. * WATER HARDNESS ON GLYPHOSATE AND GLUFOSINATE 1057 weed control, weed biomass, weed density and corn yield. Treatment means were separated using Fisher s protected LSD. The Type I error was set at PB0.05 for all statistical comparisons. RESULTS AND DISCUSSION Data were pooled and averaged over years and locations when there was no statistically significant interaction between year, location and treatments (Tables 2 to 6). There was no observable injury in corn for any of the treatments tested (data not shown). Weed Control Common lambsquarters, velvetleaf, redroot pigweed and annual grasses, primarily green foxtail (Setaria viridis L.) and barnyardgrass (Echinocloa crus-galli L.), were the predominant weeds in all years and locations. Orthogonal contrasts indicated that there was no improvement in the percent control of velvetleaf, redroot pigweed, common lambsquarters and annual grasses when AMS was added to glyphosate in all water sources at 2, 4 and 8 WAA (Tables 2 to 4). This response of glyphosate with AMS is in contrast with Pratt et al. (2003), who found that glyphosate with AMS was more efficacious for the control of velvetleaf than glyphosate without AMS. Other studies have also shown that velvetleaf control is enhanced with the addition of AMS to glyphosate (Young et al. 2003; Nurse et al. 2008). However, the control of other weed species such as common lambsquarters has not always been improved with the addition of AMS to glyphosate (Young et al. 2003; Nurse et al. 2008). It should be noted that all of these studies only reported a benefit of AMS addition at glyphosate doses B450 g a.e. ha 1, which is half the labeled dose in Ontario. Water hardness had no effect on the efficacy of glyphosate, with or without AMS, for the control of the weed species included in these experiments. In other studies, Nalewaja and Matysiak (1993) reported lower phytotoxicity with 100 ppm of Ca and 500 ppm of Mg. Pratt et al. (2003) found that glyphosate plus AMS increased weed control with both deionized and in carrier waters with antagonistic salts. Hall et al. (2000) reported that the addition of AMS to glyphosate is necessary to control velvetleaf regardless of water hardness. Generally, the addition of AMS to glufosinate resulted in improved control of velvetleaf, redroot pigweed and common lambsquarters although results were not always statistically significant (Tables 2 to 4). There was no difference in control of annual grasses at 2, 4 and 8 WAA. Glufosinate, 4 WAA, controlled velvetleaf, Table 5. Biomass (g m 2 ) of weeds treated with glyphosate (900 g a.e. ha 1 ) and glufosinate (400 g a.i. ha 1 ) with and without ammonium sulfate (AMS; 2.5 L ha 1 ) at various water hardness 10 WAA in eight field trials conducted in Ontario, Canada, during (data pooled)z Biomass (g m 2) Untreated Glyphosate 0 0.5d 1.9cde 5.2e 17.5b Glyphosate d 0.9de 7.8de 20.1b Glyphosate abcd 0.7e 13.9bcd 20.5b Glufosinate 0 3.5ab 7.6a 19.6b 56.8a Glufosinate a 5.6ab 23.4b 67.9a Glufosinate cd 2.2bcde 39.6a 66.7a GlyphosateAMS 0 0.3d 0.8de 3.7e 21.5b GlyphosateAMS bcd 1.1de 4.5e 20.2b GlyphosateAMS d 1.0de 6.6de 17.2b GlufosinateAMS 0 2.9abc 4.7abc 19.0bc 56.7a GlufosinateAMS abcd 4.3abcd 15.5bcd 50.1a GlufosinateAMS cd 5.0abc 12.4cde 61.2a Glyphosate (no AMS) vs. glyphosate (with AMS) NS (1.0 vs. 0.8) NS (1.2 vs. 1.0) NS (9.0 vs. 4.9) NS (19.4 vs. 19.6) P P P P Glufosinate (no AMS) vs. glufosinate (with AMS) NS (2.9 vs. 2.1) NS (5.1 vs. 4.7) *(27.5 vs. 15.6) NS (63.8 vs. 56.0) P P P P Glyphosate vs. glufosinate *(0.9 vs. 2.5) *(1.1 vs. 4.9) *(7.0 vs. 21.6) *(19.5 vs. 59.9) P P P P Glyphosate (no AMS) vs. glufosinate (no AMS) *(1.0 vs. 2.9) *(1.2 vs. 5.1) *(9.0 vs. 27.5) *(19.4 vs. 63.8) P P P P Glyphosate (AMS) vs. glufosinate (AMS) NS (0.8 vs. 2.1) *(1.0 vs. 4.7) *(4.9 vs. 15.6) *(19.6 vs. 56) P P P P ae Means followed by the same letter within a column are not significantly different according to Fisher s Protected LSD at PB0.05.

6 1058 CANADIAN JOURNAL OF PLANT SCIENCE redroot pigweed, common lambsquarters and annual grasses 54 to 56, 74 to 77, 65 to 69 and 68 to 71% without AMS and 60 to 66, 77 to 79, 71 to 75 and 67 to 71% with AMS, respectively (Tables 2 to 4). This increase in efficacy of glufosinate with the addition of AMS is supported by the findings of other studies (Pline et al. 1999; Maschhoff et al. 2000). While water hardness did not influence the efficacy of glufosinate on most weeds evaluated in the study, it did affect control of velvetleaf. We observed reduced velvetleaf control at 4 WAA with glufosinate plus AMS in the intermediate hard water (Table 3), and reduced velvetleaf control 8 WAA in the very hard water (Table 4). Pratt et al. (2003) also found AMS had to be added to glufosinate for the herbicide to provide consistent control of velvetleaf. Glufosinate plus AMS increased velvetleaf control when applied with deionized water and in-carrier waters with antagonistic salts (Pratt et al. 2003). Hall et al. (2000) reported that the addition of AMS to glufosinate is necessary to control velvetleaf regardless of the carrier solution hard water cations. Glyphosate with and without AMS was generally more efficacious than glufosinate at controlling velvetleaf, redroot pigweed, common lambsquarters and annual grasses (Tables 2 to 4). Glyphosate provided 27, 14, 18 and 13% greater control of velvetleaf, redroot pigweed, common lambsquarters and annual grasses than glufosinate (4 WAA) without AMS, respectively, and glyphosate provided 19, 10, 13 and 8% greater control of velvetleaf, redroot pigweed, common lambsquarters and annual grasses than glufosinate (4 WAA) with AMS, respectively (Table 3). Weed Biomass The effect of water source on biomass at 10 WAA varied among weed species (Table 5). Lambsquarters biomass was less when either herbicide was applied with AMS in very hard water. In contrast, orthogonal contrasts indicated no difference in biomass of velvetleaf, redroot pigweed, and annual grasses between glyphosate or glufosinate with or without AMS (Table 5). Glyphosate reduced weed biomass more effectively than glufosinate, whether or not AMS was applied along with the herbicide. Glyphosate without AMS decreased biomass of velvetleaf (66%), redroot pigweed (76%), common lambsquarters (67%) and annual grasses (70%) more than glufosinate with no AMS (Table 5). Similarly, glyphosate with AMS reduced biomass of velvetleaf (62%), redroot pigweed (79%), common lambsquarters Table 6. Density (no. m 2 ) for weeds and yield of corn treated with glyphosate (900 g a.e. ha 1 ) and glufosinate (400 g a.i. ha 1 ) with and without ammonium sulfate (AMS; 2.5 L ha 1 ) at various water hardness in eight field trials conducted in Ontario, Canada, during (data pooled) z Density (# m 2 ) Yield (t ha 1 ) Untreated f Glyphosate 0 2ab 3a 6b 26ab 14.0ab Glyphosate 353 1b 4a 16ab 28ab 13.7ab Glyphosate ab 3a 19ab 20b 13.5b Glufosinate 0 1b 2a 21ab 29ab 11.9cde Glufosinate 353 2ab 3a 21ab 29ab 11.7de Glufosinate b 3a 26ab 26ab 11.4e GlyphosateAMS 0 1b 3a 10ab 36ab 13.9ab GlyphosateAMS 353 2ab 4a 12ab 25ab 13.7ab GlyphosateAMS a 4a 15ab 33ab 13.9ab GlufosinateAMS 0 2ab 3a 18ab 38a 13.0bc GlufosinateAMS 353 1b 2a 24a 31ab 12.8bcd GlufosinateAMS b 3a 13ab 40a 13.4b Weed-free 14.9a Glyphosate (no AMS) vs. glyphosate (with AMS) NS (1.7 vs. 2.0) NS (3.3 vs. 3.7) NS (13.7 vs. 12.3) NS (24.7 vs. 31.3) NS (13.7 vs. 13.8) P P P P P Glufosinate (no AMS) vs. glufosinate (with AMS) NS (1.3 vs. 1.3) NS (2.7 vs. 2.7) NS (22.7 vs. 18.3) NS (28.0 vs. 36.3) *(11.7 vs. 13.1) P P P P P Glyphosate vs. glufosinate NS (1.9 vs. 1.3) NS (3.5 vs. 2.7) *(13.0 vs. 20.5) NS (28.0 vs. 32.2) *(13.8 vs. 12.4) P P P P P Glyphosate (no AMS) vs. glufosinate (no AMS) NS (1.7 vs. 1.3) NS (3.3 vs. 2.7) *(13.7 vs. 22.7) NS (24.7 vs. 28.0) *(13.7 vs. 11.7) P P P P P Glyphosate (AMS) vs. glufosinate (AMS) NS (2.0 vs. 1.3) NS (3.7 vs. 2.7) NS (12.3 vs. 18.3) NS (31.3 vs. 36.3) NS (13.8 vs. 13.1) P P P P P af Means followed by the same letter within a column are not significantly different according to Fisher s Protected LSD at PB0.05.

7 SOLTANI ET AL. * WATER HARDNESS ON GLYPHOSATE AND GLUFOSINATE 1059 (69%) and annual grasses (65%) more than glufosinate with AMS (Table 5). Weed Density There was no effect of water source on weed density reduction (10 WAA) with glyphosate and glufosinate, with or without AMS (Table 6). Orthogonal contrasts indicated there were no difference in density of velvetleaf, redroot pigweed, and annual grasses treated with glyphosate or glufosinate, with or without AMS. Glyphosate reduced density of common lambsquarters 40% more than glufosinate when AMS was not added to the spray solution, but there was no difference in weed density between these herbicides when they were applied with AMS. Corn Yield The similar levels of weed control provided among all treatments are a plausible reason for there being no effect of water hardness on corn yield with glyphosate (Table 6). Nurse et al. (2008) also reported no difference in yield when AMS was added to a full labeled dose of glyphosate (900 g a.e. ha 1 ). However, there was an 11% increase in yield when glufosinate was applied with AMS compared with when it was applied without AMS. Overall, improved weed control with glyphosate resulted in 10% greater yield than glufosinate across all water sources (Table 6). also indicated glyphosate without AMS increased yield 2 t ha 1 over glufosinate without AMS (Table 6). However, there was no difference in yield between glyphosate with AMS compared with glufosinate with AMS when all water sources were combined. In conclusion, water hardness alone had no effect on the efficacy of glyphosate for the control of velvetleaf, redroot pigweed, common lambsquarters, annual grasses or corn yield. Increasing water hardness had no effect on the efficacy of glufosinate for the control of most weeds except velvetleaf. The addition of AMS to glyphosate provided no benefit in respect to weed control and corn yield, while the addition of AMS to glufosinate improved broadleaf control with some water sources, and corresponded to an increase in corn yield. Based on these results, water hardness and AMS have no effect on the efficacy of glyphosate when it is applied at the manufacturer s recommended rate. In contrast, the efficacy of glufosinate may be increased with the addition of AMS depending on weed species and water source. ACKNOWLEDGMENTS The authors acknowledge Lynette Brown, Elaine Lepp and Christy Shropshire for their expertise and technical assistance in these studies. This research was funded in part by the Grain Farmers of Ontario (GFO) and Agricultural Adaptation Council. Bailey, W. A., Poston, D. H., Wilson, H. P. and Hines, T. E Glyphosate interactions with manganese. Weed Technol. 16: Beckie, H. J., Harker, K. N., Hall, L. M., Warwick, S. I., Legere, A., Sikkema, P. H., Clayton, G. 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