Ramularia leaf spot in barley - HGCA

Home-Grown Cereals Authority Topic Sheet 97/Summer 2007Ramularia leaf spot in barleyActionConsider treatment need of yourcurrent crop in light of losses in recentyears due to ramularia on your farm.If treatment for ramularia is considerednecessary, use a preventative spraybefore symptoms appear at bootstage – awns peeping (GS45-49).For ramularia control, apply a mixtureof either prothioconazole orepoxiconazole with chlorothalonil.Consider a strobilurin fungicide as wellfor broad-spectrum disease control.Do not apply the mildew fungicidefenpropimorph at GS49 as this mayincrease spotting.Always consider your local conditions and consulta professional agronomist if necessary.Symptoms and importanceStrong sunlight, prolonged leaf wetness, agrochemical scorch and nutritionalstress can all trigger physiological leaf spots associated with infections of thefungus Ramularia collo-cygni in barley.Symptoms comprise small brown rectangular lesions with yellow margins withinleaf veins. Lesions occur on green and dead leaves, where brown spots remainvisible. Rows of spores can be seen with a hand lens on the undersides of affectedleaves.Ramularia leaf spot poses the greatest threat to spring malting barley crops. Whilemost common in northern Britain, it can occur UK-wide as well as in Ireland,France, Germany, Scandinavia and other northern European countries. Thoughless common, ramularia on winter barley (feed and malting) can act as a source ofinoculum for the spring crop.Physiological leaf spots can be easily mistaken for net blotch. Diagnostics can helpdetermine the real cause. Ramularia also impairs quality and can increasescreenings by up to 4%.Other leaf spots caused by oxidative stress tend to be superficial browning onupper leaf surfaces, while the undersides are unaffected. Physiological leaf spotscause less yield loss, but trigger the production of ramularia leaf spots.Varietal resistanceSpring barley varieties show different levels of resistance (Table 1), but no variety isfully resistant. Potential yield losses range from 0.9t/ha in Optic, down to 0.1t/ha inDecanter. The average yield loss in high disease risk sites is 0.4t/ha.Malting crops are affected more than feed barley. This may be because maltingvarieties are more susceptible; they are also subjected to greater stress as lessnitrogen is applied.Winter barley varieties are also susceptible, but economic loss is rare since thedisease develops late in the season.Table 1. SAC resistance ratings to ramularia leaf spot in spring barleyVariety ResistanceratingCocktail 4Doyen 4Troon 5Cellar 5Optic 5Chalice 5Kirsty 5Life cycleVariety ResistanceratingNFC-Tipple 6Oxbridge 6Wicket 6Spire 6Quench 7Publican 7Westminster 7Variety ResistanceratingWaggon 7Rebecca 7Static 7Riviera 7Appalossa 8Decanter 8Power 8Rating based on 1-9 scale (not given on HGCA Recommended List).High number indicates higher resistance to ramularia.Infected seed is the main source of ramularia in spring barley. Infection can alsoresult from spores on grasses and winter barley.The ramularia fungus will spread from infected seed and grow inside barley leavesas they develop, causing no visible symptoms. Dying leaves may show signs ofinfection throughout the season, but the main damage occurs on the top leavesafter flowering.

Home-Grown Cereals Authority Caledonia House 223 Pentonville Road T +44 (0)20 7520 3922 F +44 (0)20 7520 3958London N19HYwww.hgca.comAt flowering, food reserves produced in upper leaves are diverted to the grain. Thistriggers production of a toxin, which scorches and eventually kills leaves in thepresence of light. Symptoms are most common on the most exposed upper leaves.Typical ramularia leaf spot lesions can now form. Wind spreads spores fromlesions to infect other plants, particularly when leaves are wet.ForecastingA forecast is being developed based on variety, weather (rainfall and leafwetness) and presence of spores, and including region. The forecast will helpgrowers assess the risk of crop loss as the disease spreads.Susceptible varieties are at risk if leaves remain wet for several days beforeGS49. Prolonged sunshine following wet spells will increase severity.ControlCurrent data indicates that ramularia is not controlled by seed treatments orfungicides applied at tillering.Trials were carried out in Perthshire to determine effects of various fungicides andcombinations ondisease and yield.Figure 1. Example of effects of various fungicideFigure 1 showsoptions on percent disease and yieldthe effects on% Ramularia% Dead leafpercent diseaseand distinguishes% Physiological leaf spots % Green leafspots caused by 1007.5ramularia andstress effects807.0(physiologicalspots).Prevention withfungicides can beeffective (Table 2)but correct timingis critical.Fungicidesshould be appliedbefore symptomsare likely todevelop,preferably at theboot to awnspeeping stage(GS45-49). Forinformation onfungicide doses seewww.sac.ac.uk/cropsand open the‘Fungicide DoseCurves’ window.% Leaf 26040200nilno GS49 spraystrobilurinstrobilurin + ctlRecommended options[ctl: chlorothalonil]ctltriazole + strobilurintriazoletriazole + ctltriazole + strobilurin + ctl6.56.05.55.0Yield (t/ha)Sprays were applied at GS49 to spring barley variety Optic inPerthshire in 2005. Triazoles used were epoxiconazole andprothioconazole; strobilurins were azoxystrobin andfluoxastrobin. A standard GS25 fungicide spray was applied toall, except the ‘Nil,’ treatment.OverviewAn increased incidence of leaf spottingin barley in recent years has reducedyields for some farmers, especially ofmalting crops in northern Britain.HGCA-funded projects have shownhow a fungus, ramularia, and stressconditions interact to cause spotting. Acurrent project is investigating diseaseprediction and control.HighlightsVariety choice is important to minimisedisease risk. Control measures –usually a triazole: chlorothalonil mixturespray at GS45-49 - need to be appliedbefore symptoms appear.Further informationDr Simon Oxley,Scottish Agricultural Collegesimon.oxley@sac.ac.ukTN568: Barley Disease Control(available on SAC and HGCAwebsites)Topic Sheet 57Project Report 282Ongoing project 3024The Home-Grown Cereals Authority (HGCA) hasprovided funding for this project but has notconducted the research or written this report.While authors have worked on the bestinformation available to them, neither the HGCAnor the authors shall in any event be liable for anyloss, damage or injury howsoever directly orindirectly in relation to the report or the researchon which it is based.Reference herein to trade names and proprietaryproducts without stating that they are protecteddoes not imply they may be regarded asunprotected and thus free for general use. Noendorsement of named products is intended, noris any criticism implied of other alternative, butunnamed products.Table 2. Fungicide options at GS45-49 for ramularia leaf spot controlPartner 1 Partner 2prothioconazolechlorothalonilfluoxastrobin + prothioconazole*chlorothalonilboscalid + epoxiconazole*chlorothalonilprothioconazoleazoxystrobin + chlorothalonil*epoxiconazoleazoxystrobin + chlorothalonil** Formulated mixturesRamularia leaf spot in barley Topic Sheet 97/Summer 2007Topic Sheets and Project Progress are free to levy payers.To join the mailing list contact HGCA. © HGCA 2007