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Weed Control and Yield Response to Foramsulfuron in CornAuthor(s): Robert E. Nurse, Allan S. Hamill, Clarence J. Swanton, François J. Tardif, and Peter H.SikkemaSource: Weed Technology, 21(2):453-458. 2007.Published By: Weed Science Society of AmericaDOI: http://dx.doi.org/10.1614/WT-06-071.1URL: http://www.bioone.org/doi/full/10.1614/WT-06-071.1

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Weed Control and Yield Response to Foramsulfuron in Corn

Robert E. Nurse, Allan S. Hamill, Clarence J. Swanton, Francois J. Tardif, and Peter H. Sikkema*

Foramsulfuron has recently been registered for weed control in corn in Ontario, but there is very little information on therate of foramsulfuron required to obtain at least 90% weed control. Our objective was to determine the foramsulfuron ratesgiving at least 90% weed control while maintaining crop yield loss due to weed interference and injury at less than 5%.Ten field trials were conducted at five Ontario locations (Exeter, Harrow, Ridgetown, Woodslee, and Woodstock) in 2001and 2002 to evaluate the effectiveness of foramsulfuron at rates ranging from 8.75 to 140 g ai/ha. To obtain a reduction inbiomass of 90% (I90) at 78 d after treatment (DAT), foramsulfuron must be applied to common lambsquarters at 68 g/haand to common ragweed at 86 g/ha, respectively. For green foxtail a foramsulfuron rate of 25 g/ha was required to achieve90% control. The application of foramsulfuron caused injury to corn at 7 DAT at Ridgetown and Woodstock only, butdid not exceed a rating of 10%; by 14 and 28 DAT no corn injury was recorded at any location. Corn yield of at least 95%of a weed-free check was obtained at Woodstock when foramsulfuron was applied at 70 g/ha. At Exeter and Woodsleeyield was 90% of the weed-free check at a foramsulfuron rate of 35 g/ha. Finally, at Harrow and Ridgetown, corn yield waslowered at all foramsulfuron rates because of broadleaved weed interference. Tank-mixing foramsulfuron with dicambaplus prosulfuron improved common lambsquarters and common ragweed control and final corn yield was improved bymore than 20% when compared with an application of foramsulfuron alone. Thus, these results show that weed controlwith foramsulfuron is species specific and that tank mixtures with a broadleaf herbicide may be required for broad-spectrum weed control and to protect the full yield potential of corn.Nomenclature: Foramsulfuron; common ragweed, Ambrosia artemisiifolia L. AMBEL; common lambsquarters,Chenopodium album L. CHEAL; green foxtail, Setaria viridis (L.) Beauv. SETVI; corn, Zea mays L.Key words: Integrated weed management, dicamba, nicosulfuron, prosulfuron, rimsulfuron.

Foramsulfuron is a sulfonylurea herbicide that has recentlybeen registered for weed control in corn. In Ontario,foramsulfuron is registered for application at a rate of35 g ai/ha up to the eight-leaf stage of corn (OMAF 2004).Susceptible plants are controlled through inhibition of theacetolactate synthase enzyme, preventing the production ofbranched-chain amino acids (Vencill 2002). Foramsulfuronprovides adequate control of many grass and broadleavedweeds. If applied before early tillering, foramsulfuron willcontrol annual grasses such as barnyard grass [Echinochloacrus-galli (L.) Beauv.], large crabgrass [Digitaria sanguinalis(L.) Scop.], Panicum spp. and Setaria spp., as well as theperennial, quack grass [Elytrigia repens (L.) Nevski]. Thespectrum of broadleaved weeds controlled include: redrootpigweed [Amaranthus retroflexus L.], velvetleaf [Abutilontheophrasti Medic.], Brassica spp., eastern black nightshade[Solanum ptycanthum Dun.], common lambsquarters, andcommon ragweed (Anonymous 2003).

To reduce the environmental impact of a herbicide, the rateat which 90% weed control is obtained without reducing cropsafety is an important component in the development of anintegrated weed management program (Dieleman et al. 1996;Streibig and Kudsk 1993). The rate of the herbicide must alsobe low enough to minimize the amount of the chemical beingintroduced into the environment. In corn, early-season weedcontrol is important and weed interference must be reduced

below a threshold level at which interspecific interference withthe crop does not affect yield (Cox et al. 2005; Rajcan et al.2004; Swanton et al. 1999).

When developing herbicides, agricultural products companiesand regulatory agencies must consider a broad spectrum of weedspecies to decide upon the registered rate for application.Therefore, the registered rate may be higher than the raterequired for control of the most economically important weedspecies depending on location. For example, Soltani et al. (2005)demonstrated that the herbicide flufenacet plus metribuzinapplied at a rate of 670 g/ha (170 g/ha lower than registeredrate) provided greater than 90% control of redroot pigweed,common lambsquarters, and common ragweed in soybean fieldsin southwestern Ontario. Therefore, by testing the effectivenessof a herbicide over a wide range of rates, growers will have betterinformation to determine the appropriate weed managementprogram that maximizes net returns and minimizes loading ofherbicides into the environment.

Currently, there is little information on the foramsulfuronrate required to obtain acceptable control of several weedspecies in corn. Therefore, the specific objectives of this studywere (1) to develop dose–response curves of foramsulfuron forweed control and yield in corn; and (2) to determine from thedose–response curves the rate of foramsulfuron required forgreater than 90% control of selected weed species that offersthe best crop safety in corn due to reduced early-season weedinterference.

Materials and Methods

Experimental Sites. Field experiments were conducted in2001 and 2002 at the Huron Research Station, University of

DOI: 10.1614/WT-06-071.1* Research Scientist and Research Scientist, Agriculture and Agri-Food Canada,

2585 County Rd. 20 R.R. #2 Harrow, ON N0R 1G0, Canada; Professor andAssociate Professor, University of Guelph, Guelph, ON N1G 2W1, Canada;Assistant Professor, Ridgetown College, University of Guelph, Ridgetown, ONN0P 2C0, Canada. Corresponding author’s E-mail: nurser@agr.gc.ca

Weed Technology 2007 21:453–458

Nurse et al.: Foramsulfuron in corn N 453

Guelph, Exeter, ON; Agriculture and Agri-Food Canada,Harrow, ON; Ridgetown College, University of Guelph,Ridgetown, ON; Eugene F. Whelan Experimental Farm,Agriculture and Agri-Food Canada, Woodslee, ON, and theWoodstock Research Station, University of Guelph, Wood-stock, ON. The soil at Exeter was a Brookston clay loam(Orthic Humic Gleysol, mixed, mesic, and poorly drained)with 3.8% organic matter and pH of 8.0. The soil at Harrowwas a Fox sandy loam (Brunisolic Gray Brown Luvisol) with2.6% organic matter and pH of 6.1. The soil at Ridgetownwas a Wattford/Brady loam (Gleyed Brunisolic Gray BrownLuvisol) with 4.5% organic matter and pH of 6.7. The soil atWoodslee was a Brookston clay loam (Orthic Humic Gleysol,mixed, mesic, and poorly drained) with 4.1% organic matter,and pH 6.5. The soil at Woodstock was a Guelph silt loam(Gray Brown Podzolic) with 4.8% organic matter andpH 7.7.

Experimental Procedures. Procedures at all sites were thesame unless otherwise noted. The soil at Exeter, Harrow,Woodslee, and Woodstock was moldboard plowed in the falland chisel plowed in the following spring of each year. Thesoil at Ridgetown was maintained as no-till in 2001 and 2002.Glyphosate was sprayed at 900 g ae/ha before corn plantingto control emerged weeds at the no-till Ridgetown location.Corn hybrids at all locations were seeded at approximately76,000 seeds/ha in rows 76 cm apart. Each plot was 10 mlong by 3 m wide and consisted of four corn rows, except atWoodstock where each plot was 7 m long and 3 m wide.Hybrid selection and planting date are presented in Table 1.

The experiment was organized as a randomized completeblock design with 11 treatments and 4 replications. Sixapplication rates of foramsulfuron (8.75, 17.5, 35, 70, 105,and 140 g ai/ha) were applied POST with a methylated seedoil (MSO) at 1.75 L/ha and 28% urea ammonium nitrate(UAN) at 2.5 L/ha at the four- to six-leaf stage of corn. Threetank-mix treatments were also applied: foramsulfuron(35 g ai/ha) + nicosulfuron (12.5 g/ha) + rimsulfuron(12.5 g ai/ha) + nonionic surfactant (0.2% v/v) POST;foramsulfuron (35 g ai/ha) + prosulfuron (10 g ai/ha) +dicamba (140 g ai/ha) + MSO (1.75 L/ha) + 28% UAN(2.5 L/ha) POST; and nicosulfuron (12.5 g/ha) + rimsul-furon (12.5 g/ha) + prosulfuron (10 g/ha) + dicamba (140 g/ha) + nonionic surfactant (0.2% v/v) POST. A weed-freecontrol was established by applying either S-metolachlor/

atrazine/benoxacor at 2,880 g ai/ha PRE or glyphosate at900 g ae/ha POST and maintaining with hand weeding asneeded. The final treatment was maintained as a weedycontrol. Herbicide application dates, carrier volumes, andspray pressures are reported in Table 1.

Crop injury, weed dry matter, and crop yield weremeasured at all sites. Weed dry matter harvests were madeapproximately 75 d after the application of foramsulfuronfrom a 1-m2 area within each plot. Plants were removed at thesoil surface, separated by species, and dried to a constantweight at 80 C. Injury of corn was recorded on a scale rangingfrom 0 (no visible injury) to 100 (total plant death) 7, 14, and28 d after foramsulfuron application. Corn was mechanicallyharvested at physiological maturity using a plot combine at allsites. Corn yields were adjusted to a 15.5% moisture level.The corn yields from the weed-free control were used as a basefor calculating percentage of crop yield in all plots treated withforamsulfuron.

Statistical Analysis. All data were subjected to ANOVA usingSAS statistical software.1 The data were analyzed as a mixedmodel using the MIXED procedure of SAS. The varianceswere partitioned into the fixed effects of foramsulfuron rateand into the random effects of year, location, year by location,their interactions with the fixed effects, and blocks nestedwithin year by location. The assumptions of the varianceanalysis were tested by ensuring that the residuals wererandom, homogeneous, and with a normal distribution abouta mean of zero using residual plots and the Shapiro–Wilknormality test. When the effect of location, year, and theirinteractions with foramsulfuron rate were not significant afteranalysis, data presented were pooled by location or year.

To assess weed control and estimate the rate of foramsul-furon required for 90% (I90) weed control, regression of weeddry matter over herbicide rate was performed using the log-logistic model described by Seefeldt et al. (1995) andmodified by Schabenberger et al. (1999)

Y ~ A z D { A½ �= 1 z K =100 {f½ð

K g exp B X =Ikf g�ð Þ,½1�

where Y is the response (e.g., weed dry matter), A is the lowerlimit, D is the upper limit, K is percentage reduction in weed drymatter, B is the slope of the line, Ik is the dose giving K response,

Table 1. Corn hybrids, planting dates, application date, crop stage, and average weed height at application across years and locations.

Location Hybrid Year Planting date Spray date

Weed height at application cm

Broadleaf Grasses

Exeter Pioneer 37R71 2001 3 May 18 June 5 3Pioneer 37H26 2002 22 May 11 June 5 4

Harrow Pioneer 34G81 2001 23 May 31 May 8 3Pioneer 34G13 2002 8 May 13 June 4 4

Ridgetown DK520 RR 2001 7 May 13 June 6 2DKC53-33 2002 15 May 12 June 5 3

Woodslee Pioneer 36B08 2001 9 May 13 June 4 4NK 58-01 2002 28 May 18 June 5 2

Woodstock DKC35-50AF 2001 7 May 8 June 4 2DKC35-50AF 2002 7 May 10 June 4 3

454 N Weed Technology 21, April–June 2007

and X is the herbicide rate. The rates of foramsulfuron requiredto obtain a 90% reduction of weed dry matter and the regressionparameters were estimated using the NLIN procedure in SASand were performed separately for each weed species. The dose–response curves that were generated describe the relation of theherbicide rate (on a logarithmic scale) against the percentagereduction (linear scale) of weed dry matter as a percentage ofweed dry matter in a nontreated check.

Corn yield data were subjected to an ANOVA using theMIXED procedure in SAS. The interactions of year by treatmentand year by location were nonsignificant (P . 0.05); however,the interaction of location by treatment was significant (P ,0.05). Therefore, data were analyzed separately by locationbut pooled by year for each location. Corn yields for eachlocation were converted to a percentage of the yield obtained inthe weed-free control. An ANOVA was performed on thetransformed data and confirmed that the location-by-treatmentinteraction still existed. A regression of the transformed cornyield data against herbicide rate was then performed usinga hyperbolic model described by Cousens (1985)

Y ~ I � d= 1 z I � d=Að Þ ½2�

where Y is corn yield as a percentage of yield obtained usinga standard herbicide, d is herbicide rate, I is the slope, and A is theasymptote of the hyperbolic line. The regression parameters wereobtained using the NLIN procedure in SAS and the graphicalrepresentation was generated using Sigma Plot. The curve wasused to determine the rate of foramsulfuron required to obtain atleast 95% of the corn yield that would be obtained in the weed-free plots. The 95% corn yield was designated as a yield that mustbe obtained to maintain optimal annual crop yields. Previousresearch in corn has also designated that acceptable corn yield is atleast 95% of a weed-free control or a standard herbicide treatment(Knezevic et al. 1998; Sikkema et al. 1999).

Results and Discussion

Common Lambsquarters. The control of common lambs-quarters with foramsulfuron increased with increasing foramsul-furon rate (Figure 1). Common lambsquarters populations wereabundant at all locations in both years with densities beforeforamsulfuron application as high as 300 plants/m2. The

foramsulfuron rate, required to reduce dry matter by 90%(I90), was 68 g/ha. The percentage control of commonlambsquarters was similar to that estimated by the log-logisticregression, with 76% weed control being recorded at foramsul-furon rates of 35 g/ha (Table 2). These results are similar to thosereported by Bunting et al. (2005), who obtained 81% commonlambsquarters control when foramsulfuron was applied alone ateither 32 or 37 g/ha in Illinois. Arnold et al. (2005) reported 97%common lambsquarters control with a 33 g/ha application offoramsulfuron in New Mexico. The higher level of controlobtained by Arnold et al. (2005) may be partially explained bytheir relatively low initial populations (20 plants/m2) and theapplication of foramsulfuron at an early (, 5-cm height)common lambsquarters growth stage. Larger initial commonlambsquarters populations in this study and an average seedlingheight greater than 5 cm may have contributed to thecomparatively lower common lambsquarters control in this study.

Common Ragweed. Common ragweed control increasedwith increasing foramsulfuron rate (Figure 1). Populations ofcommon ragweed were present at all locations except Harrowand initial populations ranged from 3 to 75 plants/m2. An

Figure 1. Weed dry matter (expressed as a percentage of the nontreated control)as influenced by various rates of foramsulfuron. Data points represent meanvalues (6 SE) of pooled data for CHEAL, AMBEL, and SETVI. The regressionlines were calculated using Eq. 1 and the parameter values are recorded in Table 2.

Table 2. Rate of foramsulfuron required to obtain a 90% reduction weed dry matter and regression parameters for selected weed species pooled across locationsand years.a

Weed species

Foramsulfuron rate (6 SE)b Weed control 28 DATc Regression parameters (6 SE)d

I90 35 g/ha B D A R 2

g/ha

Common lambsquarters 68 (13.7) 76 1.4 (0.27) 74 (19.3) 0.74 (0.20) 0.99Common ragweed 86 (15.5) 85 1.5 (0.34) 91 (18.9) 0.91 (0.19) 0.99Green foxtail 25 (1.5) 95 4.6 (6.2) 16 (3.0) 8.5 (1.5) 0.81

a Interactions of location and year with foramsulfuron rate were nonsignificant.b Rate of foramsulfuron resulting in a weed dry matter reduction of 90%.c Abbreviation: DAT, days after treatment.d Regression parameters were calculated using Eq. 1.

Nurse et al.: Foramsulfuron in corn N 455

86 g/ha rate of foramsulfuron was required to obtain the I90

level of weed control (Table 2). Ragweed control was 85% at35 g/ha foramsulfuron (Table 2). This result suggests thatlower rates of foramsulfuron were required to reducepopulations of common ragweed on a plant/m2 basis. Ourdata suggest that I90 common ragweed control is not possiblewhen foramsulfuron is applied at the registered rate (35 g/ha);however, it is possible to obtain greater than 80% populationreductions.

Green Foxtail. Green foxtail control increased with increasingforamsulfuron rate up to a rate at 35 g/ha, after which thelevel of control reached a plateau (Figure 1). Populations ofgreen foxtail were present at Exeter, Ridgetown, and Woods-lee at an average density of 40 plants/m2. To obtain an I90

level of control a rate of 25 g ai/ha foramsulfuron was needed(Table 2). Greater than 95% reductions in green foxtailpopulations were observed with rates of foramsulfuron 35 g/ha and above (Table 2). Bunting et al. (2004a) reportedcomparable control of a similar species, giant foxtail (Setariafaberi Herrm.), when foramsulfuron (37 g/ha) + MSO (1.0%v/v) + 28% UAN (2.5% v/v) were applied in Illinois. Buntinget al. (2004a) showed that 37 g/ha of foramsulfuron providesweed control of 98% as well as a 98% reduction in giantfoxtail biomass relative to the nontreated control.

Additional Weed Species Controlled in This Study.Redroot pigweed (Amaranthus retroflexus L.) and velvetleaf(Abutilon theophrasti Medic.) were also among the prominentweed species present at the locations tested in our study. Thedata for dry weight reductions were similar across alltreatments for both species; therefore, the log-logistic re-gression failed to converge and it was not possible to estimateI90 values for these weed species (data not shown). Therecommended registered rate of foramsulfuron (35 g/ha)provided greater than 90% control of both species (data notshown). These results are similar to the . 98% redroot

pigweed and 84% velvetleaf control reported by Arnold et al.(2005) and Bunting et al (2005).

Foramsulfuron Effect on Corn Tolerance and Yield. Corntolerance was excellent at all rates of foramsulfuron tested. AtRidgetown and Woodstock, 7 d after treatment (DAT), up to10% visual corn injury was observed at foramsulfuron ratesabove 105 g/ha (data not shown). The crop injury symptomscaused by foramsulfuron included growth reduction incomparison to the nontreated control, purpling of the leafveins and margins, a yellow flash in the whorl and patchychlorosis of corn leaves four to six. By 14 DAT corn plants didnot exhibit any visual injury symptoms, but it remains unclearif the early-season injury was reflected in the final yield. Therewas no rate-dependent association between foramsulfuron rateand corn injury. This is similar to corn injury levels at 7, 14,and 28 DAT reported by Bunting et al. (2004b, 2005).

Increasing foramsulfuron rate reduced early-season in-terference with weeds and increased corn grain yield at alllocations (Figure 2). The corn grain yields in the weed-freecheck ranged from 6.7 to 9.8 t/ha depending on location(Table 3). At Woodstock, 95% of the corn yield relative tothe weed-free check was obtained at a foramsulfuron rate ofapproximately 70 g/ha. To achieve 90% grain yield at Exeterand Woodslee, foramsulfuron rates of approximately 35 g/hawere required (Figure 2). Corn grain yield as a percentage ofthe weed-free control at Harrow and Ridgetown did notexceed 75 and 85% of the yield in the weed-free control atany of the foramsulfuron rates tested. Reduced yields atHarrow and Woodstock may have resulted from higher initialcommon lambsquarters populations prior to herbicideapplication in the foramsulfuron-treated plots.

Tank-Mixing Foramsulfuron with a Broadleaved Herbi-cide Improved Weed Control and Corn Yield. At 28 DAT,percentage weed control with foramsulfuron did not differfrom weed control observed in the nicosulfuron + rimsulfuron(standard) treatment (Table 4). Nicosulfuron + rimsulfuronhave good activity on annual grasses but must be tank-mixedwith a broadleaved herbicide to provide a broad spectrum ofcontrol. Therefore, we compared treatments of foramsulfuronand nicosulfuron + rimsulfuron that were tank-mixed with thebroadleaf herbicides prosulfuron + dicamba. There were nosignificant differences between the two tank-mix treatmentsfor weed control and the addition of prosulfuron + dicamba

Figure 2. Corn yield (expressed as a percentage of a weed-free treatment) asinfluenced by various rates of foramsulfuron at five Ontario locations. Theregression lines were calculated using Eq. 2 and the regression parameters arepresented in Table 3.

Table 3. Mean corn yield in a weed-free treatment and regression parameters(Eq. 2 and Figure 3) used to calculate rate of foramsulfuron required to achieve95% of the yield in a weed-free check across location and years.

Location YearaWeed-freecorn yield

Regression parameters (6 SE)

I A R 2

t/ha

Exeter 2001–2002 9.8 33 (8.6) 97 (2.9) 0.82Harrow 2001–2002 8.0 8 (1.5) 95 (4.8) 0.94Ridgetown 2001–2002 6.9 5 (0.7) 104 (5.3) 0.97Woodslee 2001–2002 6.7 62 (16.5) 95 (1.8) 0.79Woodstock 2001–2002 6.7 7 (1.3) 127 (8.3) 0.95

a Year-by-main effects interaction was nonsignificant. Therefore, yield data foreach location were pooled by year.

456 N Weed Technology 21, April–June 2007

improved the control of common ragweed and commonlambsquarters (Table 4). A direct comparison of foramsul-furon applied alone vs. a tank mixture with prosulfuron +dicamba revealed that the improved early-season control ofcommon ragweed and common lambsquarters resulted ina 27% increase in final corn yield. Therefore, tank-mixingforamsulfuron with a broadleaved herbicide may providebetter wide-spectrum biologically effective weed control andprotect final corn yield.

These data show that the weed control response toforamsulfuron was variable by weed species. The dose–response curves show that the most susceptible weed species inthis study was green foxtail, followed by common lambsquar-ters and common ragweed. The registered rate (35 g/ha) offoramsulfuron also provided excellent full-season control ofredroot pigweed and velvetleaf. Furthermore, these data showthat only green foxtail has the potential for control abovea 90% level at reduced foramsulfuron rates. Therefore, tocontrol a wide range of weed species and maintain corn yield,foramsulfuron must be applied at a rate of at least 35 g/ha. Infields with a combination of both grass and broadleaf weeds,an off-registered foramsulfuron rate of 70 g/ha or higherwould be required, which is higher than allowed by theherbicide registration. However, to prevent overreliance ona singular mode-of-action a more sustainable solution wouldbe to tank-mix foramsulfuron with a broadleaf herbicide.

Sources of Materials1 Statistical Analysis Systems (SAS) Software, Version 8. SAS

Institute, Inc., Box 8000, SAS Circle, Cary, NC 27512.

Acknowledgments

The authors thank Todd Cowan, Christy Shropshire, PeterSmith, and Mac Whaley for technical assistance. This work

was supported in part by Bayer CropScience and the OntarioMinistry of Agriculture, Food and Rural Affairs throughenhanced partnership with the University of Guelph.

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Table 4. Mean percentage weed control at 28 d after treatment and mean corn yield with application of foramsulfuron, nicosulfuron + rimsulfuron (standard), andforamsulfuron + prosulfuron + dicamba pooled across location and years.a

Treatmentb Rate

Visual weed control

Corn yieldABUTH AMARE AMBEL CHEAL SETVI

g ai/ha -----------------------------------------------------% ---------------------------------------------------- t/ha

Foramsulfuron 35 90 91 85 76 95 5.9Nicosulfuron + rimsulfuron 12.5 + 12.5 90 86 75 72 99 5.8Foramsulfuron + prosulfuron + dicamba 35 + 10 + 140 96 100 99 98 96 8.0Nicosulfuron + rimsulfuron + prosulfuron + dicamba 12.5 + 12.5 + 10 + 140 96 99 98 97 97 7.9LSD (0.05) 3 4 4 4 4 2Contrastsc

Foramsulfuron vs. nicosulfuron + rimsulfuron NS NS NS NS NS NSForamsulfuron + prosulfuron + dicamba vs. nicosulfuron

+ rimsulfuron + prosulfuron + dicamba NS NS NS NS NS NSForamsulfuron vs. foramsulfuron + prosulfuron + dicamba NS NS * * NS *Nicosulfuron + rimsulfuron vs. nicosulfuron + rimsulfuron

+ prosulfuron + dicamba NS * * * NS *

a Interactions of location and year with treatment were nonsignificant.b Herbicides were applied at the four- to six-leaf stage of corn.c Orthogonal contrasts denoted by an asterisk (*) are significant at the 5% level.

Nurse et al.: Foramsulfuron in corn N 457

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Received April 5, 2006, and approved November 30, 2006.

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