Always consider your local conditions and consult a professional agronomist, if necessary.

Latest information– As of 1 January 2014, the EUSustainable Use of PesticidesDirective requires priority to begiven to non-chemical methodsof plant protection whereverpossible.

– Multiple-herbicide resistant black-grass now occurs on virtually allfarms.

– This Information Sheet providesnew information on non-chemicalcontrol methods.

Action– Use several non-chemical controlmethods, in combination withherbicides, to improve overallcontrol.

– Use resistance tests to find outwhich herbicides will work on yourweeds and to monitor the successof long-term strategies.

– Tailor non-chemical control to eachindividual field; there is no single‘blueprint’ for the best strategy.

Figure 1. Increased control isneeded from pre-emergenceherbicides to compensate for thedeclining performance of post-emergence herbicides.

Black-grass.

Black-grass: solutions tothe problem

Information Sheet 30Summer 2014

Herbicide resistanceOccurrenceHerbicide-resistant black-grass hasbeen confirmed in 34 counties inEngland and has also been detectedin Scotland but at a much lowerfrequency. It is now generallyaccepted that some degree ofresistance occurs on virtually all farmson which black-grass herbicides havebeen used regularly.

Predicting the impact of resistance onan individual field is difficult because:– the proportion of plants affectedand the type of resistance variesbetween fields

– some herbicides are more affectedby resistance than others

Resistance tests are a valuablemanagement tool. Having weed seedor plant samples tested can help to:– establish whether herbicides willwork on your weeds

– avoid unnecessary use ofherbicides

– monitor the success of long-termstrategies

ImplicationsAbout 97% control of black-grass isrequired in a non-inversion tillagesystem to prevent populationsincreasing.

In the short term, ‘stacking’ severalpre-em herbicides may allowadequate overall control to be

achieved. However, as post-emherbicide efficacy falls and resistanceto pre-em herbicides increases, it isunlikely that the high levels ofcontrol needed from pre-emherbicides will be achieved routinely,especially in dry years (Figure 1).

The majority of black-grassplants now emerge withincrops, rather than beforedrilling when they could bedestroyed more easily:– 80% of black-grass plantemergence occurs in earlyautumn (August to October)

– More than 50% of winter cerealand virtually all oilseed rapecrops are sown before the endof September

Herbicides no longer offerreliable control:– Multiple-herbicide resistancenow occurs on virtually all farms

– No new active ingredients arelikely to become available in thenear future

– Some existing herbicides maybe withdrawn for regulatoryreasons

Consequently, relying solely onherbicides for control of black-grass is not sustainable in thelong term because of increasingresistance. More non-chemicalmethods will have to be used inthe future.

Why is black-grassan increasingproblem?

= achievable (<60%);

= potentially achievable(60–80%);

= unlikely to be achievableroutinely (>80%)

To achieve 97% control overall:

Control neededfrom pre-ems

If control frompost-ems is only

0% 99%

73% 89%

86% 79%

90% 69%

The agroecology of black-grassRecognising the importance of these five key factors is essential to the success of any integrated control strategy:

Emergence pattern– 80% of black-grass plants emergein early autumn, although thepattern will be affected by seeddormancy

Emergence depth– Black-grass plants mainly emergefrom seeds within 5 cm of the soilsurface

Seed longevity in soil– Average seed decline is 74% peryear

Population dynamics– More than 95% control is needed toprevent weed populations increasing

Competitiveness– Aim for fewer than 5 survivingplants/m2 to minimise yield loss andseed return

Non-chemical methods – what level of control can be achieved?The average levels of control given below are based on a comprehensive review of more than 50 field experiments: P J W Lutman, S R Moss, S Cook and S J Welham (2013), Weed Research, 53: 299–313.

The prevalence of autumn-sowncropping is the main reason whyblack-grass is an increasing problemin the UK.

More balanced rotations areneeded on many farms, not just tohelp in the control of grass weeds,but also to reduce the impact of

pests and diseases and to improvesoil fertility.

The inclusion of spring-sown cropsis likely to be the most beneficialsingle element.

Re-evaluate crop rotations for long-term sustainability.

Rotations

Ploughing reduces the risk fromgrass weeds by burying freshly shed seeds to a depth from whichseedlings are unlikely to emerge (>5 cm).

Black-grass seeds are relatively non-persistent in the seed bank(70–80% decline per year) so usuallyfewer old, buried seeds are broughtback up to the surface, especially ifploughing is done on a rotationalbasis, once every 3–6 years.

Shallow non-inversion tillagetends to favour black-grass asfreshly shed seeds are retained in

the surface soil layer from whereplants can readily emerge.

It does, however, avoid bringinglarge numbers of buried weed seedsback to the soil surface, so ispreferable where little seed has beenshed in the crop just harvested.

Failure to control black-grasseffectively in shallow non-inversiontillage systems can result in a muchmore rapid increase in infestation(more than tenfold per year) thanoccurs in systems based on annualploughing.

Plan cultivation strategy at anindividual field level to maximisecontrol of black-grass.

Ploughing (69% control)

Delayed autumn sowing of wintercereals has three benefits:1. It allows more weed seedlings to

emerge and be controlled withcultivations or glyphosate beforesowing.

2. Residual pre-emergenceherbicides can be 25–30% moreeffective when applied in laterdrilled crops because soilconditions are more favourable forgood activity.

3. Black-grass emerging in later drilledcrops tends to be less competitiveand to produce fewer seeds perplant.

These benefits can be achieved bydrilling in mid-October (or later iffeasible) rather than September butadequate soil moisture is vital tomaximise their value.

Delaying drilling carries obvious risks.These can be minimised by havingadequate drilling capacity or by usingdrills that can be used in suboptimalsoil conditions.

Delaying autumn drilling can be veryeffective but the benefit will varyfrom year to year.

Delayed autumn drilling (>31% control)

The following factors favourcompetitive crops that are betterable to suppress weeds:– higher seed rates of wintercereals (eg >300 plants/m2)

– more competitive crops, eg barleyis more competitive than wheat

– more competitive varieties

– narrow row spacing

– improved drainage

– good seedbeds

– good agronomy to achieve uniformcrops

Competitive crops will help greatlyin suppressing black-grass.

Competitive crops (22–26% control)

About 80% of black-grassemergence occurs in autumn, sospring-sown crops tend to be muchless affected and have given aconsistently good reduction inweed infestation in field trials.

Spring barley is more competitivethan spring wheat but there is alack of information on theeffectiveness of other spring-sown

crops and the impact of differentspring sowing dates.

Establishing crops in spring can bedifficult, especially on heavy soils,and herbicide choice is more limited.

Choose the most appropriate springcrops for the individual farm.

Spring cropping (88% control)

Seed persistence data and farmexperience both support the viewthat a one-year fallow or grass leyis not long enough to reduce highblack-grass infestations toacceptable levels.

After two years, less than 10% ofseeds are likely to remain – a muchmore significant reduction. A grassley break of 2–3 years is also a verygood option, provided such fieldscan be used effectively.

Failure to prevent seed return willgreatly undermine the value of afallow or grass ley break.

The cultivation strategy at the end ofany fallow or grass ley break isimportant. Sufficient time shouldelapse between cultivating andsowing the next crop to allow thedestruction of black-grass seedlingsemerging from residual seeds.

Fallowing and grass ley breaks havea valuable role to play in weedcontrol in modern arable systems.

Fallowing/grass ley breaks (70–80% reduction of the seed bank per year)

Spraying off patches of black-grassin winter wheat with glyphosate inthe first week of June will preventviable seed return. Considerspraying the same areas for 2–3years to maximise reductions.Cutting, or spraying in May or laterin June, is likely to be lesseffective.

Minimise spread of seeds andplants in combine harvesters,

balers, cultivation equipment, strawor manure.

Hand rogueing is feasible at lowweed populations and is particularlyrecommended in fields where black-grass is only just starting to appear.It may already be resistant if it hasbeen introduced from the mainarable areas of England incontaminated straw, for example.

Take action to minimise theintroduction and spread of weedseeds.

Preventing seed return and spread of resistant seeds

Information Sheet 30Summer 2014

HGCA publications are free to levy payersTo join the mailing list, contact: subscriptions@hgca.ahdb.org.uk

© Agriculture and Horticulture Development Board 2014. All rights reserved.

While the Agriculture and Horticulture Development Board, operating through its HGCA division,seeks to ensure that the information contained within this document is accurate at the time ofprinting, no warranty is given in respect thereof and, to the maximum extent permitted by law, theAgriculture and Horticulture Development Board accepts no liability for loss, damage or injuryhowsoever caused (including that caused by negligence) or suffered directly or indirectly in relationto information and opinions contained in or omitted from this document.

Reference herein to trade names and proprietary products without stating that they are protecteddoes not imply that they may be regarded as unprotected and thus free for general use. Noendorsement of named products is intended, nor is any criticism implied of other alternative butunnamed products.

HGCA is the cereals and oilseeds division of the Agriculture and Horticulture Development Board.

Integrated Weed Management (IWM)Reliance on herbicides alone is not a sustainable strategy and, as of 1 January 2014, the EU Sustainable Use of Pesticides Directive (2009/128/EC)requires priority to be given to non-chemical methods of plant protection,wherever possible.

Further informationPaul Gosling, HGCApaul.gosling@hgca.ahdb.org.uk

Stephen Moss, RothamstedResearchstephen.moss@rothamsted.ac.uk

G61: Managing weeds in arablerotations – a guide (HGCA, 2014)

IS17: Weed control inconventional and organic oats(HGCA, 2012)

TS116: Autumn grass weedcontrol in cereals and oilseedrape (HGCA, 2012)

G47: The encyclopaedia of arableweeds (HGCA/BASF, 2009)

www.hgca.com/weeds

A review of the effects of cropagronomy on the management ofAlopecurus myosuroides. P J W Lutman, S R Moss, S Cookand S J Welham (2013). Weed Research, 53: 299–313

Black-grass (Alopecurusmyosuroides) (RothamstedResearch, 2013)

Black-grass: the potential of non-chemical control (RothamstedResearch, 2013)

www.rothamsted.ac.uk/black-grass-and-herbicide-resistance

The benefits of herbicideresistance testing (WeedResistance Action Group, 2012)

Weed Resistance Action Group

HGCA PublicationsT 0845 245 0009E hgca@cambertown.comwww.hgca.com

Figure 2. Potential benefit of integrating use of several non-chemicalmethods with herbicides.

Integrating the use of several non-chemical methods, in combinationwith herbicides, should improveoverall control. Figure 2 shows atheoretical example, based on thevalues for control on the previoustwo pages.

In this example, the four non-chemical methods give a combinedlevel of control of 90% (note that thisis not simply the sum of the controlfrom the individual methods). Then,assuming that herbicides give 90%control, the overall control in thisexample is 99% – the sort of levelrequired to prevent black-grassincreasing.

– The poorer the control fromherbicides, the greater the needfor non-chemical methods.

– Integrating the use of severalnon-chemical methods, incombination with herbicides,should improve overall control.

– Recognise that there is no‘blueprint’ for the best non-chemical control strategy;approaches need to be tailored tothe weed and resistance problemin each individual field.

– Consider the relative cost ofcontrolling black-grass byherbicides and non-chemicalmethods; herbicides may nolonger be the cheaper option onsome fields.

– Lack of ‘resistance’ to non-chemical methods means theyshould provide more durablecontrol than herbicides; learninghow to get the best out of themat the individual farm level willpay dividends in the long term.

Key messages

1000 -

800 -

600 -

400 -

200 -

0 -

Bla

ck-g

rass

pla

nts/

m2

Potentialweed

infestation

Ploughing Delayeddrilling

Higherseedrates

Competitivevarieties

Herbicides

1000

31069%

214

31%

158

26%

123

22%

12

90%

Overall reduction = 99%