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Barley leaf and head diseases : barley yellow dwarf virus (BYDV), smut, leaf rust
More information available on:
Leaf and head diseases: scald and net blotches
Leaf and head diseases: mildew, leaf spot and other diseases
Root diseases: Take-all, Rhizoctonia and Root Lesion Nematode
Other root diseases:
Cereal Cyst Nematode, Fusarium Crown Rot, Common Root Rot and Pythium Root Rot
The development of leaf and head diseases in barley can reduce yield and grain quality. Monitor this risk by inspecting crops at fortnightly intervals from mid tillering stage to grain filling and taking action if required.
Inspect the crop by walking a systematic W pattern. Stop at regular intervals checking all leaves on nearby plants to gain an understanding of what diseases are present and their level of infection. Assess the risk by considering:
- disease type and amount
- varietal tolerance
- stage of crop growth
- potential yield
- cost of control measures
- risk of future disease infections
If necessary, submit crop samples to the AGWEST Plant Laboratories for diagnosis (WA growers only).
| Barley Yellow Dwarf Virus | Covered Smut | Loose Smut | Barley Leaf Rust |
Related Links
- Note 288: Managing barley leaf diseases [Replaces Farmnote Farmnote 64/2001] [PDF 46KB]
- Farmnote 65/2001: Leaf diseases of barley [PDF 201KB]
Barley Yellow Dwarf Virus (BYDV)
| Symptoms | Source of Infection and Spread | Conditions Favouring Disease | Control |
BYDV is transmitted by cereal aphids. Once infected, a plant cannot be "cured" and significant damage can be caused by only a few aphids moving through a crop. Historically, high rainfall zones of the WA grainbelt have been most prone to yield losses from BYDV, and in many years very little BYDV has been seen in low rainfall zones. However, when aphids arrive exceptionally early in the lower annual rainfall areas BYDV spread does occur although the extent of yield losses in these areas is unknown. The virus can occur widely in years of high aphid activity as the virus mainly depends on conditions favourable for early aphid activity and build up. Crops are most sensitive to this disease in the first 8 to 10 weeks after emergence.
Field experiments have shown yield losses of 12 to 15 % are typical with this disease although losses of up to 50 % in highly susceptible varieties are possible under disease favourable conditions.
Aphids can also cause direct feeding damage to barley plants if they build up to high enough numbers to "starve" the plant by removing water and nutrients for their own use. Yield losses from aphid feeding damage can occur across all rainfall zones. Outbreaks of cereal aphids and epidemics of BYDV are sporadic and in many years may not require control. However yield losses can occasionally be severe and effective control is required.
Symptoms
Initial infection occurs in very young crops (four to eight weeks) when aphids first arrive. This gives rise to infected individual plants scattered through the crop. From these plants colonising aphids spread the infection to nearby plants causing small, circular areas of yellow stunted plants. Yellowing progresses down the leaf from the tip. Tillering can be stimulated by infection but most tillers then develop poorly and may produce sterile heads. Severely affected plants may be stunted with bright yellow leaf tips and pale stripes between leaf veins. When the head emerges, awns are twisted and the head may be sterile. Symptoms may be confused with those of nutritional deficiencies and waterlogging.
Source of Infection and Spread
The virus is spread by the cereal aphids Rhopalosiphum maidis (corn aphid) and Rhopalosiphum padi (wheat/oat aphid).
The virus requires living plant tissue to survive and cannot survive in stubble or soil. Infection in the plant is restricted to the conducting tissue (phloem). Once an aphid gets the virus from feeding on an infected plant it continues to transmit it to any plant it feeds from for its entire life.
In WA, BYDV survives the summer in perennial grasses growing in roadside ditches or at the edges of creeks or rivers. However, grasses surviving in swamps, irrigated pastures and gardens are also hosts. The four most important host species are kikuyu grass, paspalum grass, couch grass and african lovegrass.
Conditions Favouring Disease
- Summer rain Summer and early autumn rain which results in volunteer cereals and growth of perennial pastures will lead to a build-up in aphid numbers.
- Sowing date Early sowing increase the level of disease. In the southern areas, April sown barley is particularly susceptible. This may be a result of the early rains that allow the crop to be sown early but are also favourable for the build-up of aphids. Research has shown that delaying sowing to June can markedly reduce the level of BYDV infection. In general it is not recommended to delay sowing to reduce BYDV as yield penalties from late sowing are likely to outweigh the benefits of reduced disease level.
Control
- Varietal resistance
When sowing early, use a tolerant variety if appropriate. BYDV consists of a number of closely related virus strains and resistance may be ineffective if certain strains predominate. Varieties such as Gairdner and Baudin carry the Yd2+ gene which confers resistance to BYDV in Western Australia, whereas varieties like Stirling, Hamelin, Vlamingh and Mundah do not carry any genes for resistance to BYDV.- Insecticide
In high risk areas, treating the seed with seed dressing containing the active ingredient imacloprid can significantly reduce the risk of BYDV infection. When sowing a susceptible variety in high-risk areas and when aphids are reported in a district, treating the crop with an aphicide can reduce BYDV infection substantially. When spraying aphids to control BYDV, it is necessary to spray at the first sign of aphids. Even if the variety sown carries resistance to BYDV, spraying an insecticide will reduce the effects of aphid feeding on screenings and consequently grain yield.
Related Links
- Note 288: Managing barley leaf diseases [Replaces Farmnote 64/2001] [PDF 146KB]
- Farmnote 65/2001: Leaf diseases of barley [PDF 201KB]
- More about BYDV
Covered Smut
| Symptoms | Source of Infection and Spread | Control |
Covered smut, caused by the fungus Ustilago segetum var. hordei is easily controlled by the use of seed dressings and therefore is not often seen in Western Australia unless untreated seed is sown and harvested repeatedly. However, covered smut (classified as Ball smut by CBH) can cause downgrading of the grain at delivery to a receival point.
Symptoms
The first sign of the disease is when dark compacted heads emerge form the flag leaf and remain conspicuous and intact until harvest. In these infected heads, smut balls take the place of the grain. Unlike loose smut, the smutted heads remain intact until harvest when spores are spread onto the outside of healthy seed so that the disease is externally seed-borne. Fragments of infected heads in harvested grain are a tell-tale sign of the disease.
Source of Infection and Spread
The smutted balls are broken and crushed during threshing, releasing spores that collect on the outside surface of the barley seeds. After seeding, the spores germinate at the same time as the seed and infect the seedling through the coleoptile. The optimum temperature for infection is from 20 to 24 C.
Control
Fungicide seed dressings effectively control covered smut. However in-furrow fungicides are not registered for the control of covered smut.
Related Links
- Farmnote 65/2001: Leaf diseases of barley [PDF 201KB]
- Farmnote 27/1987: Cereal smuts - life cycles [Expired][11 KB]
| Symptoms | Source of Infection and Spread | Conditions Favouring Disease | Control |
Loose smut, caused by the fungus Ustilago tritici is widespread in the medium to high rainfall areas of Western Australia. This is a potentially serious disease if not kept under control by the use of seed dressings.
Symptoms
The first sign of the disease is when the infected heads emerge from the flag leaf as a mass of dark brown powdery spores. These spores are blown off in the wind leaving inconspicuous bare stalks that may be the only sign of the disease late in the season.
Source of Infection and Spread
This disease is internally seed borne. Infected seed appears normal but carries a minute dormant infection inside the embryo. When the infected seed germinates, the fungus becomes active and grows slowly in the growing point of the plant. Diseased plants appear normal until heading, but may be taller and mature earlier than surrounding healthy plants. The fungus now grows rapidly and forms a compact spore mass to replace the cereal head. The black powdery spores blow away to leave a bare stalk (rachis). The spores are released as the rest of the crop is flowering and they infect the developing grains of healthy heads, remaining dormant in the grain until that seed is sown the next season.
Seed from crops infected with loose smut usually have between 1 and 10 per cent infected seed but occasionally more. Infected plants produce little or no grain.
Conditions Favouring Disease
The disease is most common in cool high rainfall areas and may be more common in the year following a wet spring, which promotes seed infection.
Control
The disease is controlled by treating the seed with a systemic fungicide that penetrates the developing seedling to kill the internal infection.
Trial work by Dr Kith Jayasena and Geoff Thomas of the Department of Agriculture and Food has found that fungicides with active ingredients of triadimenol (e.g. Baytan), triticonazole (e.g. Real) and tebuconazole (e.g. Raxil) were effective in reducing loose smut incidence by 60 - 100 % at three DAFWA trial sites (Avondale, Mt Barker and Gibson) in 2005 but did not eradicate it completely. Difenoconazole (e.g. Dividend) was not effective at reducing smut, and neither were fertiliser applied fungicides like triadimefon in-furrow.
At around $6/ha for Baytan and $14/ha for Real, these products additionally offer 6 weeks protection against powdery mildew infection of the seedlings over products like Raxil. How the seed is treated is critical, as a common complaint heard is that the fungicide is not effective against smut, when in most cases it is poor application coverage that is the main reason for any problems.
More importantly, sourcing seed from areas with the lowest possible exposure to smut is cost effective as there is a direct relationship between percentage of infected heads and yield. Seed with greater than 5 % infection should not be used, and new clean seed sourced, while seed with less than 5 % infection should be treated each year with a seed dressing effective against smuts.
At a yield of 2.5 t/ha with farm gate price of $156 /t, returns drop by $39 /ha as a 10 % infection causes a 10 % yield reduction. Even at $6 /ha for the application of Baytan, growers will come out $33 /ha better by managing loose smut with the added benefit of reducing powdery mildew infection.
If seed lines are known to carry high levels of loose smut they should not be sown as seed dressings cannot completely control infection if disease is severe. Use new disease-free seed that has been treated.
Check your crops for loose smut by walking frequently through the crop at flowering. Infections should be dealt with before they become too severe.
Related Links
- Farmnote 65/2001: Leaf diseases of barley [PDF 201KB]
Barley Leaf Rust
There are different strategies for applying fungicides to manage barley leaf rust depending on the disease development. For fungicide options, see the current DAFWA Cereal Foliar Fungicide Chart.
Under 2 t/ha yield potential
If the flag-2 leaf or lower leaves have very obvious (>10%) leaf rust infection, apply the appropriate fungicide at early flag leaf emergence (Z37).
Over 2 t/ha yield potential
Crop infection at tillering to early stem elongation
If barley leaf rust is detected during tillering to early stem elongation of the disease spreads quickly from the lower leaves to upper leaves during stem elongation (bottom three leaves have 10 % rust, upper leaves have scattered pustules), two applications of a fungicide may be required.
- first application to be at stem elongation (Z31-32). Use higher rates if infection is abundant.
- a second application four weeks later or when the flag leaf fully emerges (Z39) may be required if actively sporulating infections remain visible.
Crop infection at early stem elongation but prior to head emergence
If conditions favour development of disease, then yield losses of around 20% are possible. Apply the fungicide between stem elongation and early flag leaf emergence if bottom leaves have 10 % rust and associated yellowing and upper leaves have scattered pustules.
Crop is infected after head emergence
Yield losses of up to 10 % may occur. This yield loss will result from a decrease in grain size. Malting varieties that have a narrower grain shape will benefit more from a fungicide application at this stage.
Related Links
- Farmnote 65/2001: Leaf diseases of barley [PDF 201KB]
- Cereal foliar fungicides registered for use on cereals in Western Australia : current at June 2007 [Updated 18 June 2007]
Page amended : 21 June 2007
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