Red Leather Leaf – not just a tongue twister!

Red leather leaf (RLL) is a common fungal disease caused by Spermospora avenae, that reduces hay and grain yield, reduces grain quality and impacts hay appearance and colour. In Victoria we are beginning to see evidence of infection this season.

RLL infection is favoured by cool (5-16°C), wet conditions so is more predominant in medium to high rainfall areas. Agriculture Victoria paddock surveys during 2019 found RLL in 90 per cent of oat crops sown in medium and high rainfall areas, but was uncommon and much less severe in low rainfall zones.

Primary infection begins during cool, wet weather from mycelium on seed and spores from stubble, followed by secondary infection of the upper canopy from splash and wind dispersed spores.

Losses are also most likely during seasons with wet winters and early springs as this favours disease development on the top two leaves.

The AgriFutures National Hay Agronomy project is currently investigating best practice management options for Red Leather Leaf, and other oat diseases affecting oaten hay crops across southern Australia.

What to look for
Generally, you begin to see symptoms of RLL at mid tillering to early stem elongation.

(Photo source: Agriculture Victoria)
Initial infection symptoms appear as pale blue coloured lesions with a red/ brown edge, typically during tillering.
(Photo source: Agriculture Victoria)
Later in the season, affected leaves have a red/brown ‘leathery’ appearance, large irregular shaped lesions and may roll slightly.

Impact on production
Due to the impact on the leaf, RLL can have a detrimental impact on hay quality by reducing hay biomass, height and stem thickness, while milling oats incur grain yield losses with reductions to grain plumpness (screenings) and weight.

Field experiements conducted by Agriculture Victoria 2018 and 2019 showed that red leather leaf severity was greatest in susceptible rated varieties. Red leather leaf caused up-to 0.7 t/ha (16%) grain yield loss in milling varieties and up to 1.0 t/ha (12%) biomass loss in hay varieties.

Both seasons had below-average rainfall, particularly during spring months, so losses would likely be greater during seasons with greater rainfall.

What can you do about RLL
RLL management needs a coordinated approach.

  • Crop rotation: RLL is stubble borne so avoid sowing oats into oat stubble. Allow 2–3 years before re-sowing oats into the same paddock to allow RLL inoculum to breakdown.
  • Variety choice: Grow moderately susceptible (MS) or better rated varieties to reduce the risk of production loss during favourable RLL seasons. Unfortunately, commonly grown varieties Mitika, Mulgara, Wintaroo and Yallara are susceptible to RLL. Variety

Red leather leaf

VarietyRed leather leaf
BannisterMSS
BilbyMS
BrusherMS
DurackS
ForesterMRMS
KowariMS
MitikaS
MulgaraS
TungooMS
WilliamsMS
WintarooS
YallaraSVS

MR = moderately resistant                    MRMS = moderately resistant to moderately susceptible
MS = moderately susceptible                 MSS = moderately susceptible to susceptible
S = susceptible                                        SVS = susceptible to very susceptible

  • Fungicides: Foliar fungicides registered for other diseases in oats have been found to provide suppression of RLL and grain and hay yield benefits, but do not provide total control.

Agriculture Victoria is investigating the effectiveness of fungicides and application timings on RLL suppression. Best RLL suppression has been achieved when fungicides are applied at mid-tillering (Z25) to stem elongation (Z31), coinciding with early disease development. Later applications were less effective. During more favourable seasons though, a second fungicide application may be required as one application is unlikely to provide lasting suppression.

Fungicides are also being evaluated for prolonging green leaf retention and suppression of weather damage caused by saprophytic fungi that colonise hay post cutting. In 2019, treatments of propiconazole at Z25, Z31 and Z55, and propiconazole at Z25 and Z31 and pyraclostrobin + epoxiconazole at Z55, both reduced saprophytic fungi and mould growth and reduced hay discolouration post-cutting. Yeast colonisation increased. Research is ongoing evaluate these fungicide effects in other seasons, and the effects of late applications on minimum residue limits.

Remember to follow fungicide label rates and withholding periods for oats, and rotate fungicides with different modes of action to minimise the opportunity for fungicide resistance developing.

A National Hay Agronomy 2020 Disease Review has recently been completed by the National Hay Agronomy pathology team, and provides current information on RLL and other diseases affecting oaten hay crops. Additionally, you can find the latest information on Twitter using the #NationalHayAgronomy.

Acknowledgements
The AgriFutures National Hay Agronomy project is part of the AgriFutures Export Fodder Program, and is a collaborative effort between the Department of Primary Industries and Regional Development WA, the South Australian Research and Development Institute, the Department of Primary Industries NSW, Agriculture Victoria, and a number of grower groups including BCG.

BCG trials at Rupanyup and Curyo are evaluating oaten hay yield and quality responses to variety, time of sowing, nitrogen rates, time of cutting and use of plant growth regulators.

Milling oat research is being supported by GRDC.

References
Agriculture Victoria Cereal disease guide 2020
Managing red leather leaf disease and preventing weather damage in oats

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