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Barley leaf and head diseases : scald and blotch
Barley Home - Causes of Disease
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| Scald | Net-Type Net Blotch | Spot-Type Net Blotch |
Scald
| Symptoms | Source of Infection and Spread | Conditions Favouring Disease | Control |
Scald is one of the most widespread leaf diseases of barley in Western Australia and is caused by the fungus Rhynchosporium secalis.
Scald is more common in the southern high rainfall areas but in wet years can be obvious in medium rainfall regions. Scald is potentially very damaging in barley as an infection can kill leaves prematurely and reduce seed weight. A severe early infection can reduce the number of heads and grains/head. In highly productive crops, yield losses of up to 45% are possible with associated quality defects.
Symptoms
Lower leaves are usually affected first by Scald. The first sign of the disease is a blue/grey/green water-soaked area on the leaf. These lesions become bleached with a distinctive brown margin. Lesions are most commonly seen on the leaf blades but are also seen on the leaf sheath and head when the level of infection is high.
Source of Infection and Spread
The most common source of primary infection is from the residue of a previously infected crop or barley grass. Spore release and spread from stubble occurs with rain. Spores splash on and infect emerged barley plants and form the primary infection in the crop. Scald can also be spread on the seed from an infected crop.
Rain-splash also spreads spores within the crop canopy. Scald is often seen as 'hot spots' within the crop indicating that the initial infection has taken place in the centre of the worst affected area or 'hot spot' and then spread to neighbouring plants by splash.
Conditions Favouring Disease
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Temperature and moisture
The optimum temperature for both spore production and infection is 15 to 20C. Rain aids the spread of disease and the most rapid increase in disease is observed early in spring when temperature and moisture conditions are ideal. -
Sowing date
Early sown crops develop higher levels of scald. Early sown crops may be exposed to the heaviest release of spores from infected residues. The disease can develop in the upper leaves of the plant when conditions are favourable to the spread of disease. -
Nutrition
Disease is more severe at higher levels of nitrogen supply.
Control
In disease prone environments, select a resistant variety if available. If sowing a susceptible variety use a seed-applied fungicide with foliar activity or fertiliser applied fungicide to control scald infections early in the season. Foliar fungicides can be used to reduce disease. Do not double crop barley in medium to high rainfall areas as this can result in severe disease unless the stubble is destroyed. Where the wind erosion risk is low, burning stubble can reduce the carry-over of the fungus if double cropping.
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Varietal resistance
There is a large range in varietal resistance among commercially grown varieties. When sowing early, use a resistant variety wherever possible. Varietal resistance may eventually break down. The fungus is highly variable and may eventually be able to attack a previously resistant variety of barley.Avoid sourcing seed from a severely affected crop. The disease may be introduced into a paddock on infected seed.
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Rotation
Do not sow into barley stubble as this potentially has a high risk of a severe outbreak occurring. A minimum break of one year will significantly reduce the potential for a serious disease outbreak. -
Seed treatment
Apply an appropriate seed dressing or in-furrow fungicide in medium to high rainfall areas if growing a susceptible variety or if seed is from an affected crop. -
Foliar fungicide
Apply a fungicide spray if the disease threatens a well-grown crop (potential >3t/ha). Apply before head emergence if many hot spots are seen during stem elongation or if active infections are on middle canopy leaves. An application of a foliar fungicide is most feasible in high risk areas or a regions with a high yield or quality expectation. -
- Cereal foliar fungicides registered for use on cereals in Western Australia : current at June 2007 [Updated 18 June 2007]
Related Links
- Note 288: Managing barley leaf diseases [Replaces Farmnote 64/01] [PDF 146KB]
- Farmnote 65/01: Leaf diseases of barley [PDF 201KB]
- Farmnote 65/2001: Leaf diseases of barley [PDF 201KB]
Net-Type Net Blotch
| Symptoms | Source of Infection and Spread | Conditions Favouring Disease | Control |
Net blotch is one of the most widespread leaf diseases of barley in Western Australia. Two types of the fungus occur, net-type and spot-type, which have different symptoms and distributions.
Net-type net blotch, caused by the fungus Pyrenophora teres f. teres, is the most common form. It occurs throughout the barley growing areas of Western Australia but is more common in the medium and low rainfall areas. It is very problematic in double-cropped paddocks.
A severe infection of net-type net blotch (NTNB) may cause premature leaf death and reduce the seed weight. It may also reduce the number of heads and the number of grains per head. Yield reductions of 20 to 30 per cent can occur and grain quality (screenings, protein, hectolitre weight) may also be affected.
Symptoms
Symptoms appear on susceptible varieties as small brown blotches that elongate and form thin brown streaks along and across the leaf blade. This often forms a net like pattern surrounded by yellowing. Severely affected leaves wither rapidly. Lesions can be restricted on less susceptible varieties.
Source of Infection and Spread
The fungus is carried from season to season on infected barley stubble. Spores produced on stubble or straw are spread by wind to initiate infections in new barley crops. Infected residue can produce spores for over two years.
Although seed infection has been observed in Western Australia, significant transmission of seed infection to seedlings is rare. Infected seed is currently of minor importance in the spread of NTNB in Western Australia.
Conditions Favouring Disease
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Temperature and moisture
The optimum temperature for spore production and infection in 15-25C. Spore release occurs at near 100 % relative humidity. Infection of barley leaves is greatest when humid, moist conditions persist for 10 to 30 hours or longer. -
Sowing date
Early sowings increase the level of disease. In southern areas, April sown barley is particularly prone to net blotch.
Control
-
Rotation
Do not double crop barley in medium to high rainfall areas as this can result in severe disease. In disease prone areas ensure barley is grown only once in three year rotations. -
Varietal resistance
Avoid growing highly susceptible varieties. In disease prone environments select a resistant variety if available. -
Barley stubble
Manage crop residues when not rotating crops. Tillage practices that incorporate the residue into the soil and help its breakdown or burning stubble will reduce the abundance of the disease pathogen. This must be balanced against the increased potential for soil erosion. -
Seed treatment
An appropriate seed dressing may be effective against the seed borne pathogen but is ineffective against an infection that arises from airborne spores. -
Foliar fungicide
No foliar fungicide has yet been registered for net-type net blotch in Western Australia.- Cereal foliar fungicides registered for use on cereals in Western Australia : current at June 2007 [Updated 18 June 2007]
Related Links
- Note 288: Managing barley leaf diseases [Replaces Farmnote 64/01] [PDF 146KB]
- Farmnote 65/01: Leaf diseases of barley [PDF 201KB]
Spot-Type Net Blotch
| Symptoms | Source of Infection and Spread | Control |
Net blotch is widespread in barley crops in Western Australia. Two types of the fungus occur, net-type and spot-type which have different symptoms and distributions.
Spot-type net blotch is caused by the fungus Pyrenophora teres f maculata. This disease is most damaging in southern coastal and neighbouring environments where it can have a severe impact on yield and quality. Outbreaks have also occurred in northern agricultural areas, around Badgingarra.
The incidence of spot-type net blotch has increased with the adoption of stubble retention practices and with the increase in the area sown with susceptible barley varieties such as Franklin and Gairdner.
A severe infection of spot-type net blotch may result in premature leaf death and poor grain development. Management in disease prone environments is vital, as severe infections can reduce grain size, which leads to a high level of screenings and the downgrading of malt varieties to feed grade.
Research in the northern agricultural region has shown yield losses of 3 to 22 per cent from the disease. In the southern region, yield losses of up to 34% have been measured in the long season humid environment of the coast where extremes of the disease have been observed.
Spot-type net blotch is different from spot blotch, a leaf disease occurring in the eastern states of Australia. Spot blotch has not been identified in Western Australia.
Symptoms
PSpot-type net blotch appears as elliptical dark brown spots with yellow edges. As the spots age they elongate and join together causing blotch symptoms. The elongated spots are the most distinctive feature compared with the related net-type net blotch which has a net-like appearance. Symptoms of both pathogens can vary with varietal resistance.
Source of Infection and Spread
The fungus survives on infected barley stubble over summer. With autumn rains, the fungus produces spores that are dispersed by wind and can be blown a moderate distance (kilometres) onto young barley crops. As the disease develops, spores of the fungus are also produced on the dead leaves. Secondary infections develop when these spores infect newly developing leaves, encouraged by wet weather. Disease severity will generally be higher in well-grown crops that have a dense canopy that retains moisture on the leaves for a longer period of time. Drying spring conditions slow the cycle of infection.
Conditions Favouring Disease
-
Temperature and moisture
Spore production occurs between 15 and 25C with an optimum of about 20C. The release of spores occurs at near 100% relative humidity. Rain and heavy dew provide ideal conditions for the primary infection. -
Sowing date
Early sowings may increase the development of disease because of early favourable conditions. With a favourable start, spot-type net blotch can then progress at the same rate as crop growth throughout the season. This results in maximum disease impact on grain yield. In southern areas, early sown crops of Gairdner and Baudin that are well grown are particularly prone to infection by spot-type net blotch.
Control
Effective control of spot-type net blotch requires a combination of management options.
- Rotation Crop rotation is a key aspect of management. In high risk areas follow a crop rotation of at least one in three years of barley in the same paddock. Unfortunately, spores produced from infected stubble are readily dispersed by wind and spores from neighbouring crop stubble or even those several kilometres away, can still initiate disease. Nevertheless, the risk of early disease diminishes with the increased distance from the previous season's stubble. Crops that are placed upwind (for winds prevailing during the early stages of crop development) will be less prone to early infection than downwind crops.
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Barley stubble
Destroying the previous season's stubble that is close to new barley paddocks can reduce early disease infection. Tillage practices that incorporate the residue into the soil helping it to break down and stubble burning will reduce the abundance of the disease pathogen. This must be balance against the increased potential for soil erosion by wind. -
Varietal resistance
Growing resistant varieties is probably the most appealing management option. All varieties now grown in Western Australia are susceptible or moderately susceptible to spot-type net blotch except Schooner, Onslow and Barque.
Selecting a plump-grained variety reduces the risk of downgrading of malt varieties to feed grade. E.g. High levels of this disease reduce grain weight. This may affect the quality of narrow-grained varieties such as Gairdner by increasing screenings from 10 to 40 per cent. There may be only a minor effect on plump-grained varieties such as Stirling -
Avoid very early sowings
Don't sow Gairdner or Baudin in April in areas that have a high risk of this disease developing. -
Seed treatment
No seed dressing fungicides are currently registered for effective control of infections that arise from air-borne spores. -
Foliar fungicide
This disease is difficult to control with fungicides. Apply a propiconazole-based fungicide at the early or late stem elongation stage if the disease becomes prevalent in high risk areas. -
- Cereal foliar fungicides registered for use on cereals in Western Australia : current at June 2007 [Updated 18 June 2007]
Related Links
-
Farmnote 107/99: Spot-type net blotch leaf disease of barley [PDF 218KB]
- Farmnote 65/2001: Leaf Diseases of Barley [PDF 201KB]
- Note 288: Managing barley leaf diseases [Replaces Farmnote 64/2001] [PDF 146KB]
Page amended : 21 June 2007
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