There are five different rusts that can infect barley. Each varies in importance depending on variety susceptibility, seasonal conditions and control strategies in place.

• Leaf rust, caused by Puccinia hordei, is common in high rainfall areas and can also occur in other areas during wet Grain yield losses of up to 20% are possible if favourable conditions occur.
• Stem rust, caused by Puccinia graminis, is uncommon but can cause severe crop losses of up to 40% grain yield loss during wet and warm seasons.
• Barley grass stripe rust, Puccinia striiformis sp. pseudo-hordei, is very common on barley grass and can infect some susceptible varieties. However, it generally does not result in grain yield loss.
• Barley stripe rust, caused by Puccinia striiformis sp. hordei is an exotic disease that has the potential to cause severe infections and grain yield losses of up to 30%.

Leaf rust occurs most years in susceptible barley varieties, particulaly in high rainfall regions. Early infections (July – August) can result in yield losses of up to 20%.

Stem rust is potentially the most devastating disease of the rusts diseases and although rare can cause complete crop loss if favourable conditions occur.

Barley grass stripe rust is common, but is unlikely to cause yield loss. The exotic pathogen barley stripe rust will cause severe losses of up to 30% in most barley varieties, if it is introduced to Australia.

Rust Disease Cycle

(See Wheat Rust Life Cycles)

The primary source of inoculum for leaf rust is volunteer barley plants that survive over summer. Development of leaf rust is most rapid during warm (15-20°C), moist (rain or dew) weather. Crops with late maturity, particularly following a wet summer are often more severely infected. The ‘Star of Bethlehem’ (Ornithogalum umbellatum) weed can be a source of inoculum and is a host for the alternate, sexual stage of teleospores. The sexual cycle results in the emergence of new strains that can overcome existing resistances. Currently, the Star of Bethlehem weed is found in South Australia, with isolated occurrences across the Victorian cropping zone.

Leaf Rust: What to Look For

Pustules of leaf rust are small and circular producing a mass of orange-brown powdery spores, predominantly on the upper leaf surfaces. These pustules easily rub off on a finger when touched. Later in the season, pustules also develop on leaf sheaths. As the crop matures, the pustules turn dark and produce black spores embedded in old plant tissues. Leaf rust can be confused with stem rust, but are distinguishable by colour and size-leaf rust pustules are lighter in colour, smaller and rounder than those of stem rust.

Stem Rust: What to Look For

Pustules are large, oval to elongated and are often surrounded by a characteristic torn margin. The pustules are full of reddish, brown spores which dislodge easily. Pustules can occur on stems, leaf surfaces, the leaf sheaths and heads. As the plant matures, the pustules produce black spores that are firmly embedded and do not dislodge.

Barley Grass Stripe Rust: What to Look For

Symptoms resemble stripe rust in wheat. Bright yellow- orange spores form pustules that occur in stripes along the leaves.

On young leaves, the pustules tend to be scattered across the leaf. Spores rub off easily onto a finger when touched. Barley grass stripe rust and Barley stripe rust have identical symptoms. If unusually severe symptoms observed, it could indicate the presence of exotic barley stripe rust, which must be reported via the Exotic Plant Pest Hotline (1800 084 881).

 

Management of Rusts

Resistant Varieties

The most effective way to control the three rusts of barley is to grow varieties with resistance. Resistant varieties offer several benefits:

• Reduce the amount of disease in a crop and in neighbouring crops.
• Lower the chance of the rusts mutating, reducing the chance of them being able to attack previously resistant varieties.
• Preserve the effectiveness of resistant varieties currently available.

Nevertheless, it is important to note that new races of barley rust can emerge and overcome resistance in some varieties. To select varieties with effective resistance, it is essential to consult a current Victorian Cereal Disease Guide or the NVT (National Variety Trial) website when selecting varieties.

Cultural Practices

These rusts survive predominantly on volunteer barley plants during summer/autumn, which provide significant inoculum loads if left unmanaged. Effective management strategies involves; removing self-sown barley, use grazing and/ or herbicides to eliminate green bridge, especially during wet summers, and aiming to eliminate the green bridge prior to March for greatest benefit.

Seed Treatment

Fluxapyroxad is registered for the control of Barley leaf rust and can help prevent early infection. Fungicides applied via seed treatment or fertiliser can also suppress early leaf rust development. However, its efficacy may vary between seasons, and a follow up foliar fungicide application may be required later in the season in high disease pressure.

Fungicides

A range of foliar applied fungicides are available for suppressing leaf rust in barley. Research by Agriculture Victoria and Birchip Cropping Group has shown that the most effective strategy of managing leaf rust was the application of foliar fungicides at early in the epidemic. Additional applications may also be required in seasons with sustained rust pressure, particularly during a wet spring.

Seed applied fluxapyroxad and fertiliser applied fungicides are registered for the control of barley leaf rust. These fungicides can prevent early infection; however, efficacy is likely to reduce significantly as the season progresses. Continue to monitor crops during the season as a follow up application of foliar fungicide may be necessary if the epidemic persists during the spring months.

 

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