Canwemanagebromeandbarleygrassincereals?

SallyPeltzer,AbulHashemand AlexDouglas,DepartmentofAgricultureandFood,WesternAustralia,Albany, NorthamandKatanning.

Key messages

  • The pre-emergent application of metribuzin, trifluralin orBoxer Gold® followed by Monza®reduced barley and brome grass by over 80percentwith good wheat yields. The combinationof metribuzinand Monza® isthe cheapest toapply.
  • Donotrely on the stand-alone usage of pre- and post-emergent herbicides to completely controlbarley grassandbrome grass in cereals.
  • These grasses need tobe strategicallymanaged prior to sowing tocereals.

Background and aim

Thelast few seasons have hadlate starts promptingmany farmers tosow directly onthe break oreven dry. Thelack of effective pre-planting control (coupled with theadoption of conservation tillage)hasresulted in widespreadincreases inbarley grass (Hordeumleporinum) and brome grass (Bromusdiandrusand B. rigidus) in cereals.

Thereisa lack ofeffective post-emergent herbicides forthe controlofbarley grass and bromegrass intraditional wheat varieties. Alternatives include using metribuzin-tolerant wheat varieties such as EagleRock orClearfield varieties which canbesprayedwith Midas® or Intervix®. Arethese effectivetreatments forthe control of brome and barley grassontheir own?Dowe also need to considerintegrated weed management techniques such as thecontrolof seed setinthepreviousseason orone or two knockdowns prior to sowing?

Thistrial investigates thecontrolof barley grass and brome grass inwheat usingpre- and post-emergent herbicides.

Method

A site at Katanning (Great Southern Agricultural Research Institute) wasselectedin 2008 withabackground population ofbarleygrass (Hordeumleporinum Link.) and great brome (BromusdiandrusRoth). The trial was sown to Eagle Rock® wheat andClearfield Janz® wheaton3 June 2009, oneweek after the break oftheseason. Thebarleyandbromegrasswasattheone-leaf stage. The trialhada randomisedsplit-plot block design with11 herbicide treatments and 4 replicates. Thetreatmentswerea rangeof pre-emergent herbicides either applied singly orin combination witha post-emergentherbicide. There wereno knockdowns applied.

Measurements taken throughout the season included crop and weed densities, dry weights at anthesisandyield andgrain protein.

This trialwas repeated at Beverley on aheavy infestation of barley grass.

Herbicidetreatments
Eagle Rock®wheat

1.Metribuzin (750 g/kg) at150 g/ha, IBS

2.Metribuzin (750 g/kg) at 200 g/ha,IBS+ Monza® (sulfosulfuron) (750 g/kg) at25g/ha,PO

3.Boxer Gold® (S-metalochlor (120 g/L) + prosulfocarb (800 g/L)) at2.5 L/ha, IBS

4.Boxer Gold® (S-metalochlor (120 g/L)+ prosulfocarb (800 g/L)) at2.5 L/ha, IBS +Monza®(sulfosulfuron)(750 g/kg) at 25g/ha,PO

5.Trifluralin (480 g/L) at 2 L/ha IBS

6.Trifluralin (480 g/L) at 2 L/ha IBS + Monza® (sulfosulfuron) (750 g/kg) at 25 g/ha, PO

7.Diuron (900 g/kg) at 450 g/ha, IBS

8.Diuron (900 g/kg) at 450 g/ha, IBS + Monza® (sulfosulfuron) (750 g/kg) at 25 g/ha, PO

9.Monza® (sulfosulfuron) (750 g/kg) at25g/ha,PO

10.Untreated

Clearfield Janz®wheat

1.Intervix® (imazamox (33 g/L) + imazapyr 15g/L))at 500 mL/ha,PO (Z14–37)(Note:IBS= incorporated by sowing, PO= post-emergent.)

Results

A slowstart to the season and non-wetting resulted ina staggeredgermination of the wheat but agood germination of barley grass. Early countsindicated that approximately 100 barley grassandbromegrass plants (/metre2) germinatedacross the trial. Barley grasswas the predominant grassweed although brome grass and annual ryegrass were also present.

All of the pre-emergent herbicides resulted in somecontrol (50–70per cent) of barley grass in EagleRock® wheat, as shown bythehead numbers, althoughnone werecompletely effective (Figure 1).Anadditional post-emergentapplication ofMonza® furtherimproved barley grasscontrol. The applicationofMonza®after metribuzin, Boxer Gold® and trifluralin controlled both grassesbyover80 per cent. Applied as asingle application, Monza®only marginally reduced the number of barley headsbutthesizeoftheindividual heads was decreased. Itwassprayed 6weeks after sowing andthe grasseswere possiblylittle too big.In Clearfield Janz®, Intervix® alsocontrolled barley grass by over 80percent reducingthe number and size of the barley grass heads anddelaying their emergence. Similarresultswere found at Beverley.

Although thebrome grassnumbers were low across the trial, only metribuzin, Boxer Gold® andtrifluralinincombination with Monza® reduced head numbers.

250

200

barleygrassbromegrass

150

100

50

0

Figure 1.Theeffectof11herbicidetreatmentsonthenumberofbarleyandbromegrassheads(heads/m2)in Eagle Rock® and Clearfield Janz®wheat.

The high numbers of grass weeds inthecrop resulted in reduced wheatyieldsbyover60 per cent(Figure 2). The metribuzinand Monza® treatmenthadthe highest yieldandthelowest weedcount butthis was not significantly differentthanarange of other products. The greater the number of bromeand barley grass present, the greater the reduction inyield.Clearfield Janz® was the exceptionhowever; producing poor yields despite reasonable controlof barley grass.Thisvariety seemed tostrugglewith the dry start to the season compared with Eagle Rock®.

1.60

1.20

0.80

0.40

0.00

Figure2:The effect of barleyand bromegrass control by11 herbicide treatmentson the yield (t/ha) ofEagleRock®andClearfieldJanz®wheat.

Conclusions

  • Itisdifficultto effectivelycontrol barley grassand brome grass incerealswith pre- and post-emergent herbicides alone.The pre-emergent applicationof metribuzin followed by Monza®reduced barley and brome grass by over 80percent and produced the best yield.Otherpre-emergents such astrifluralin andBoxerGold®in combinationwithMonza® alsocontrolledthegrassweedsand producedgood yields butare more expensive toapply.The application ofIntervix®alsocontrolled barley grass toover80 per centbuttheyieldsof Clearfield Janzwerepoor. This variety struggled with the late start to the season.
  • Inthistrial,someofthe herbicide treatments reducedthe number of barley grass heads by80percent but there werestill over 30 heads/m2 produced. These heads can produce over750weedseeds/m2to compete with your crop in the following season.
  • Integratedweed management should beemployedtocontrol barleyand brome grass.Strategically-timed pasture spray-toppingin the previous seasoncan reduce bothbarley grassandbrome grass seed setbyover85 per centand should beconsidered when planning to cropafter pasture.Over99 per centof barley grass andBromus diandrus(the bromegrassspeciesinthistrial)seeds germinate within1–2weeksofthe break oftheseason. Theseseedlings canthenbe effectively controlled using knockdowns prior to sowing. The yieldlossattributedtothedelayedsowing is likely to be less than the yieldlossdue to weedcompetition. The use of otherrotations, such as herbicide-tolerant canola, may effectively controlthese grasses.

Key words

brome grass, barley grass,herbicides, ITwheat, Clearfield wheat, Monza, metribuzin, trifluralin, BoxerGold®, diuron, Intervix®

Acknowledgments

IwouldliketothankVince Lambert (GSARI) and Paul Matson (Albany) fortheirhelpinthemanagement of this trial. I would also like to thank GRDC for their financial support.

Project No.:GRDCUA00105

Paper reviewedby:John Moore