Barley scald is caused by the fungus Rhynchosporium commune (formerly known as R. secalis) and is common in all barley growing regions. Its severity varies significantly within a given crop, between crops and seasons, depending on seasonal conditions. It is most prevalent in high rainfall seasons, particularly following an early and wet season break. Grain yield losses in susceptible varieties are generally 10-20% , while individual crop losses can be as high as 40%.
What to Look For
Scald causes lesions on the leaf blades and sheaths. At first, scald appears as water-soaked, grey green lesions, which change to a straw colour with a brown margin that are ovate to irregular in shape.
In severe infections, the disease can cause complete defoliation by coalescing of the lesions.
Scald of barley. Early water-soaked, grey-green symptoms with a distinctive brown margin. (Photo: Agriculture Victoria).
Scald of barley. Later straw coloured lesions with a distinctive brown margin. (Photo: Agriculture Victoria).
Scald of barley showing symptoms under sever conditions: large, straw-coloured lesion with brown margins, coalescing to cause extensive leaf loss. (Photo: Unknown).
Disease Cycle
R. commune (Scald) survives over summer and autumn on stubble of infected plants. Spores are dispersed from the stubble during Autumn by rain splash into the new season’s crop, initiating primary infection. Scald is usually first observed in isolated patches during tillering or early stem elongation. Further spread can be rapid during warmer conditions (15-20ºC) and is caused by splash dispersal of spores. By the end of the growing season scald can be found throughout the crop with distinct hotspots. The disease is most severe in above average rainfall seasons, particularly during the winter and spring.
Scald can also be seed-borne, can infect barley grass and survive on volunteer barley plants. Although, these sources are less important than infected stubble, they can be a source of inoculum, particularly in seasons with favourable climatic conditions.
Disease cycle of barley scald. Illustration by Kylie Fowler
Management
Cultural Practices
Carry-over of scald inoculum can be reduced by using crop rotations that avoid consecutive barley crops, ideally with a two year or longer break between barley crops. This allows infected crop residue to breakdown naturally, thus reducing the risk of disease carry-over. Grazing, burning and cultivation of stubble, volunteers and barley grass, can reduce inoculum loads. However, these practices do not eliminate the disease entirely, as the scald pathogen, R. commune can survive on small amounts of remaining residue. Scald is also more severe in early sown crops, so avoid early sowing of susceptible varieties, especially in high rainfall areas to reduce the risk of loss caused by scald.
Resistant Varieties
Cultivation of resistant varieties gives the best control of scald, with the risk of grain yield and quality loss being greatly reduced by avoiding growing susceptible and very susceptible rated varieties. Unfortunately, R. commune is highly diverse pathogenically, thus capable of rapidly overcoming plant resistances. As a result, many varieties are susceptible to current strains. It is essential to consult current Victorian Cereal Disease Guide or the NVT website to get to know the resistance status of barley varieties
Fungicides
There are a range of fungicides available that will provide suppression of scald. Fertiliser and seed applied fungicides provide effective suppression during the seedling stages of crop development, while foliar fungicides are most effective when applied during the beginning of stem elongation (GS31) to flag leaf emergence (GS39) stages. Two applications of fungicide are generally required to minimise grain yield and quality loss in season with sustained disease pressure. Fungicide applications that coincide with the early stages of scald development are more effective than later applications. Delayed applications may be less effective as scald can rapidly damage leaf tissue when conditions are favourable.
Regular crop monitoring is essential during seasons with risk of scald development.
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