Control Postemergente Arvejas

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Weed Science Society of America

Postemergence Weed Control in Pea (Pisum sativum) with ImazamoxAuthor(s): Robert E. BlackshawSource: Weed Technology, Vol. 12, No. 1 (Jan. - Mar., 1998), pp. 64-68Published by: Weed Science Society of America and Allen PressStable URL: http://www.jstor.org/stable/3988690 .

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Weed Technology. 1998. Volume 12:64-68

PostemergenceWeed Controlin Pea (Pisumsativum)with Imazamox'ROBERTE. BLACKSHAW2

Abstract: Few postemergence(POST) herbicidesare available for broad-spectrumweed control inpea. Field experimentswere conducted to determinethe suitabilityof imazamox to provideselectivecontrol of grassand broadleafweeds in pea. Imazamoxcontrolledseveralgrassandbroadleafspecies,but the rate required to attain 90% control ranged from 7 to 36 g ai/ha dependingon the weedspecies. Imazamoxefficacy differed with the adjuvant ncludedin the spraymixture.Mergeadjuvantoften increased mazamoxactivityon weeds morethan Sun-ItII methylatedseed oil or a combinationof Agral 90 adjuvantplus 28-0-0 liquid fertilizer.Pea exhibitedexcellent tolerance to imazamox upto the highest rate applied,40 g/ha. Pea yield comparableto that of the hand-weededcontrol wasattained with 20 to 30 g/ha of imazamox. Imazamox offers growers a POST option for broad-spectrumweed control in pea.Nomenclature: Imazamox, 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-(methoxyme-thyl)nicotinicacid; barley, Hordeumvulgare L. 'Galt'; canola, Brassica rapa L. 'Tobin';commonlambsquarters,Chenopodium lbum L. #3 CHEAL;greenfoxtail, Setariaviridis(L.) Beauv.# SETVI;pea, Pisum sativa L. 'Carneval';redrootpigweed, AmaranthusretroflexusL. # AMARE; redstemfilaree, Erodium cicutarium(L.) L'Herex Ait. # EROCI;wild oat, Avenafatua L. # AVEFA;wheat,TriticumaestivumL. 'Katepwa.'Additional index words: Adjuvants, herbicide efficacy, pea yield, Agral 90, Merge, Sun-It II,AMARE, AVEFA,CHEAL, EROCI,SETVI.

INTRODUCTIONPea is a legume crop producedon 0.5 million ha on

the Canadianprairies. It provides a good economic re-turn to growers and fits well in rotationswith cerealsand oilseeds commonly grown in this region.Weeds competevigorously with pea, andyield reduc-tions of 20 to 40% are common (Blackshaw andO'Donovan 1993; Wall et al. 1991). Trifluralin2,6-di-nitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine),ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dini-tro-4-(trifluoromethyl)benzenamine], ethoxydim 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen- -one, and imazethapyr2-[4,5-dihydro-4-methyl-4-( 1-methylethyl)-5-oxo- lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylicacid are the most prevalentherbicides used by prairie pea growers (Anonymous1997). Adoption of conservationtillage practices in re-cent years has led to increased use of postemergence(POST) herbicides. Sethoxydim controls only grass

' Received for publication June 25, 1997, and in revised form October 3,1997.2Weed Scientist, Research Centre, Agriculture and Agri-Food Canada,P.O. Box 3000, Lethbridge,AB, CanadaTIJ 4B1; [email protected] Lettersfollowing this symbol are a WSSA-approved omputercode fromComposite List of Weeds, Revised 1989. Available from WSSA, 810 East10th Street,Lawrence, KS 66044-8897.

weeds. Imazethapyr controls several broadleaf weedsand some grasses but not wild oat or volunteerwheatand barley.Additionally,some growersare reluctanttouse imazethapyrbecause its soil persistence is sufficientto injuresome rotationalcrops planted1 yr or morelater(Moyer and Esau 1996).Imazamox(formerly AC 299,263) is a new imidazo-linone herbicidethatis reported o controla large num-ber of grass and broadleafweeds and has shown selec-tivity in a numberof crops includingpea (Anonymous1994). Initialstudiesindicatethatsoil persistenceof im-azamox is less than that of imazethapyr(Anonymous1994). This study was initiatedto determine(1) the re-sponseof severaltroublesomegrass andbroadleafweedsto various rates of imazamox, (2) the effect of variousadjuvants on imazamox efficacy, and (3) the effect oftheseimazamoxtreatments n peayield underconditionstypical of the Canadianprairies.

MATERIALS ND METHODSField experiments were conductedin 1995 and 1996at Lethbridge,AB. The soil was a Typic Haploborollwith a sandy clay loam texture, pH 7.8, and 3.6% or-ganic matter.Priorto seeding in the spring,fertilizerwas

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broadcastand incorporatedo bringthe total N and P to120 and40 kg/ha, respectively. Carnevalpea was seededin early May with a double-diskpress drill at 200 kg/hato a depth of 4 cm with 23-cm row spacingon land thathad been fallowed the previous year.Herbicideefficacyindicatorspecies were sown perpendicular o the plotsin adjacent 1.5-m wide stripswith the same drill. Greenfoxtail, wild oat, wheat, and barley were sown in thegrass weed control experiment;common lambsquarters,redroot pigweed, redstem filaree, and canola in thebroadleaf experiment; and wild oat, barley, commonlambsquarters,and canola in the adjuvantexperiment.Otherweed species were removedby handpulling on abiweekly schedule.Treatments n the grass and broadleaf weed controlexperimentsconsisted of imazamox4at 5, 10, 15, 20, 25,30, and 40 g ai/ha. Agral 905 surfactant at 0.25% v/vand 28-0-0 liquid fertilizer at 2% v/v were includedwith all treatments.Treatments n the adjuvant experi-ment consisted of imazamox at 10, 15, and 20 g/ha eachwith Merge6 at 0.5% v/v, Sun-It 117 at 1.25% v/v, orAgral 90 at 0.25% v/v plus 28-0-0 liquid fertilizer at2%v/v. Weedy andhand-weededcontrols were includedin all experiments.Treatmentswere appliedwhen grassweeds had threeto fourleaves, broadleafweeds had twoto four leaves, and pea had three to five leaf whorls.Herbicideswere appliedwith a small plot bicycle spray-er delivering 100 L/ha at 205 kPa. In all experiments,treatmentplots were 2 by 6 m arrangedn a randomizedcomplete block design with four replications.Pea tolerance to the herbicide treatmentswas ratedvisually on a percent scale 2 to 3 wk after herbicideapplication. Abovegroundweed fresh weight was deter-mined in respective 0.5-M2 areas in each plot shortlybefore harvest.Pea yield was determinedby harvesting4 m2 from the center portion of each plot. Harvestedsamples were cleaned before weighing.All data were subjectedto analysis of variance(ANO-VA). Visual pea tolerance ratings were arcsine trans-formed priorto ANOVA (Steel and Tome 1980). Weedbiomass data in the grass and broadleafcontrolexperi-ments were subjectedto regressionanalysis andfitted tothe following exponential model (Mead and Cumow1983):

4Imazamox was supplied by CyanamidCanada Inc., 88 McNabb Street,Markham,ON, Canada L3R 6E6.I Agral 90 is 90% nonylphenoxy polyethoxy ethanol available from Ze-neca Agro, PO. Box 9910, Stoney Creek, ON, Canada L8G 3Z1.6Merge is a proprietyadjuvantsupplied by BASF CanadaInc., 345 Car-lingview Drive, Toronto, ON, Canada M9W 6N9.7 Sun-It II is methylated seed oil available from AGSCO, Inc., GrandForks, ND 58204.

Y = A exp(-BX) [1]where Y is weed biomass,A is the untreatedweed bio-mass, X is herbiciderate, and B is the proportionalde-crease in weed biomass with increasingherbiciderate.The regressionmodel for pea yield in these experi-ments was Y = A - B exp(-CX) [2]where Yis pea yield, A is the asymptoticpea yield, X isherbiciderate, B is the decrease in pea yield withoutherbicide (A - B = intercept), and C is the proportionalchange in pea yield with herbicide rate.Treatmentmeans of the weed biomass and pea yielddatain the adjuvant xperimentwere comparedby singledegree of freedom contrasts(Steel andTorme1980). Allstatistical ests andequationfittingwereperformedusingSAS (SAS 1989).

RESULTSAND DISCUSSIONAnalysis of data over years indicated a significant(P

< 0.05) year by treatmentnteraction or the weed bio-mass andpea yield data. The nonlinearregressionmodelfit the datawell, with R2values of 0.9 or greaterfor allequations(Figures 1 and 2). From the fitted regressionlines, a predicted90% reductionin green foxtail shootbiomass occurred with 13 and 15 g/ha of imazamoxin1995 and 1996, respectively (Figure 1). Wild oat bio-mass was reduced90%by 16 and 22 g/ha of imazamoxin 1995 and 1996, respectively. Imazamoxat 9 and 18g/ha controlled wheat, and 14 and 23 g/ha controlledbarley, in 1995 and 1996, respectively.Imazamox efficacy differed more among broadleafthan grass weed species. Redroot pigweed and canolawere controlled at much lower rates of imazamox thancommon lambsquartersor redstem filaree (Figure 2).Redrootpigweed shoot biomass was reduced90% by 7and 12 g/haof imazamox n 1995and 1996, respectively.Imazamoxat 18 and 16 g/ha caused a 90%reduction ncanola biomass in 1995 and 1996, respectively. In con-trast,28 and 25 g/ha of imazamox was needed to givea 90% reduction n redstemfilaree biomass in 1995 and1996, respectively.A 90%reduction n common lambs-quartersbiomass required23 and 36 g/ha of imazamoxin 1995 and 1996, respectively.Harveyet al. (1995) sim-ilarly reported greater than 90% control of commonlambsquarterswith imazamox at 26 to 35 g/ha. NelsonandRenner(1995) foundthatimazamoxat 35 g/ha pro-vided 81 and 87% control of common lambsquartersntwo separatestudies.

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3500 Greenfoxtail Wildoat3000 -2500 -1995\

200 -- 1996 02000 v- - -1 996 \? 1995: Y=3087*e -0.124X, R2=0.96E 1500 - 1996: Y=749*eO?76X, R2=0.941000 1995: Y=962*e-0l62X R2-=0. 91 1996: Y=322*e Ossx, R2-O.99 ocn 500-A

0 ~~-EO 3500 Wheat Barley0 3000 X 1o 2500 ; 1995: Y=3214*e- 37X, R2=0.97- 2000 - 1995: Y=2515*e-O19OX,R2=0.97 8 1996: Y=2615*e-0?67X, R2=0.90CD) 1996: Y=1391*e-0096X, R2=0.941500

1000 0500 - ~

0 -0 00 10 20 30 40 0 10 20 30 40Imazamox rate (g/ha)

Figure 1. Shoot biomass response of green foxtail, wild oat, wheat, and barleyto imazamoxrate.

Pea was not visibly injuredby imazamoxat any ratein either year (data not shown). A previous study re-portedless than 5% visible injury to pea by imazamoxapplied at rates up to 70 g/ha (Harvey et al. 1995). Peayield respondedpositively to imazamoxappliedto con-trol grass or broadleafweeds in both years (Figure 3).

Pea yield tended to plateauat imazamoxrates of 20 to30 g/ha, indicatingthat weed competitionwas minimalat theserates.Weedswere eitherkilledor severely stunt-ed by imazamoxapplied at these rates.Imazamox at 20to 30 g/ha resulted in similar pea yield to that of therespective hand-weededcontrols (365 and 182 g/m2 in4000 Redrootpigweed Canola3000

o-0 1995 \ 1995: Y=3905*e-0..24X R2=0.99c 2000 .--- 1996 1 996: Y=956*e-0lsx, R2 0.98:) 1000 \ 1995: Y=2608*e442, R2=0.99

1996: Y=586*e207X, R2=0.99 A -AL

? 4000 Commonlambsquarters Redstemfilaree0 3000 -o 0

U) 2000 1995: Y=1306*e0089x, R2=0.94 0 1995: Y=3230*e067X, R2=0.921996: Y=1097*e -?51x, R2=0.91 1996: Y=421*eox68x, R2=0.941000 0

00 0 -0 10 20 30 40 0 10 20 30 40

Imazamox ate(g/ha)Figure 2. Shoot biomass response of redrootpigweed, canola, common lambsquarters, nd redstemfilareeto imazamoxrate.

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500- Grass weeds400- 1300 -

CY 200- A 1996 -0:) 1004 t'1995: Y=377-202*e0ll3x1R2=0.981996:Y=201-94*e0l39xR2-0.97

- 500- Broadleaf weedsa)OoXn 400-

X 300 >g200z/---4__100 1995:Y=454-259*e0l1ox,R2=0.961996:Y=251-76*e&0'06X,2= .96

0 10 20 30 40Imazamox rate (g/ha)

Figure 3. Pea seed yield response to imazamox applied at various rates tocontrol weeds.

the grass weed experimentand 427 and 238 g/m2in thebroadleaf weed experimentin 1995 and 1996, respec-tively).In the adjuvantexperiment, a significant(P < 0.01)year by treatmentby weed species interactionoccurredfor weed biomass andpea yield data.Imazamoxefficacyon canola was less dependenton the choice of adjuvant

than with the other species (Table 1). In 1995, efficacyon canola averagedover all imazamox rateswas greaterwith Merge than with either Agral 90 plus 28-0-0 orSun-It II (Table 1, Contrasts1 and 3). However, at thehighest rate of 20 g/ha of imazamox,all adjuvantswereequally effective (Table 1, Contrasts4 and 5). In 1996,there were no differences among the three adjuvants ntheir effect on imazamox efficacy on canola (Table 1,Contrasts1, 2, and 3). Merge was the superioradjuvantwith imazamoxon barleyand common lambsquartersnboth years and on wild oat in 1996 (Table 1, Contrasts1 and 3). In 1995, Merge increased imazamox efficacyon wild oat more than Sun-It (Table 1, Contrast3) butwas similar to Agral 90 plus 28-0-0 (Table 1, Contrast1). Merge remained the most efficacious adjuvantonwild oat, barley,and common lambsquarters ven at thehighest rate of 20 g/ha of imazamox in most instances(Table 1, Contrasts4 and 5). Imazamox efficacy wasgreaterwhen combined with Agral 90 plus 28-0-0 thanwith Sun-It II on wild oat in both years and barley in1995 (Table 1, Contrast2). However,no differenceswerenoted between these adjuvantson barley in 1996 or oncanola and common lambsquarters n either year (Table1, Contrast2).

Pea was not visibly injured by any imazamox-adju-vant combination in either year (data not shown). Peayield respondedpositively to these imazamox treatmentsin both years (Table 2, Contrast 1). Averaged over allrates of imazamox, there were no differences among the

Table 1. Shoot biomass of indicatorplants treatedwith imazamoxappliedat various rates and with variousadjuvants.Wild oat Barley Canola Commonlambsquarters

Treatmenta Rate 1995 1996 1995 1996 1995 1996 1995 1996g/ha g/m2

1. Weedy control 0 2,873 775 2,309 2,374 3,734 446 1,041 3202. Imazamox + A + F 10 1,254 293 882 1,483 1,198 98 879 3163. Imazamox + A + F 15 370 143 311 1,210 382 62 519 2654. Imazamox + A + F 20 221 69 128 1,176 136 14 255 1465. Imazamox + M 10 1,001 122 426 642 565 23 414 2566. Imazamox + M 15 319 75 241 127 220 0 279 947. Imazamox + M 20 93 89 11 59 110 6 143 368. Imazamox + S 10 1,370 505 1,128 1,644 833 47 821 2819. Imazamox + S 15 808 591 816 1,576 288 32 457 28410. Imazamox + S 20 638 287 512 1,100 92 12 211 206

Single degree of freedom contrastsbWild oat Barley Canola Commonlambsquarters

1995 1996 1995 1996 1995 1996 1995 19961. 2-4 vs. 5-7 NS * * ** * NS ** **2. 2-4 vs. 8-10 ** ** ** NS NS NS NS NS3. 5-7 vs. 8-10 ** ** ** ** * NS * **4. 4 vs. 7 * NS * ** NS NS * NS5. 7 vs. 10 ** ** ** ** NS NS * **

a Adjuvant abbreviations:A = Agral 90 at 0.25% v/v; F = 28-0-0 liquid fertilizer at 2% v/v; M = Merge at 0.5% v/v; and S = Sun-ItII at 1.25% v/v.b Significancelevel: NS = not significant; *P < 0.05; **P < 0.01.

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Control Postemergente Arvejas