Ramularia leaf spot (RLS) is a disease that attacks barley crops late in the season; losses are linked to reductions in photosynthetic area.
As is the case with many plant diseases, stressed crops are more likely to show symptoms.
However, once symptoms develop on the upper leaves, post-flowering, treatment is not effective; disease management is all about control prior to its onset.
Ramularia
Teagasc’s Deirdre Doyle discussed the issue of RLS control at the 2023 National Tillage Conference.
She explained that barley crops must produce high numbers of productive tillers in order to maximise final yields.
“The tillers produced by the plant must be protected from disease,” she explained.
“Where fungicide use is concerned, it’s important to come in at growth stage 31/32 to deliver protection for the lower leaves.
“This should be followed up with another application between growth stages 45 and 49, in order to protect the upper canopy.”
But there are a number of control-related challenges, where RLS is concerned.
Chief among them is the loss of chlorothalonil as a disease control chemistry. Fungicide resistance, more generally, is another issue, as is the unreliability of varietal resistance.
Deirdre Doyle continued:“Teagasc conducted an RLS trial on spring barley between 2019 and 2022. All the products used were applied at the awns emerging stage; the recommended rate for each product was used.
“The key parameters assessed were actual disease control achieved and final yields.”
The final results of the work confirm that Folpet, when applied at a rate of 500g/ha, works well within a spring barley scenario.
However, separate trial work on winter barley crops, again carried out by Teagasc, has confirmed the yield benefits of including Folpet as part of a fungicide programme.
When applied as part of a tank mix at growth stage 37 and again between growth stages 45 and 49, the chemistry delivered high yield improvements relative to an untreated control.
Resistance
Doyle went on to point out that varietal resistance is, to all intents and purposes, not available yet.
Agronomic practices will have an impact on RLS prevalence. The bottom line here is that climatic conditions and various tank mixes can have an impact on stress levels.
Growers must also provide adequate nutrition to minimise the stress within a crop.
And where fungicide use is concerned, the primary objective is to build a programme that will protect the crop. Both tillers and the upper canopy must be protected.
And, finally, Teagasc is recommending the use of Folpet in RLS programmes.