Symptoms

The disease can be recognised by the orange to brown coloured rust pustules on the plant. The rust pustules produce a fine powder like substance when rubbed. These pustules are slightly raised and occur on both sides of the leaves and very occasionally on the stem, leaf sheaths or ears. Late in the season, some blackish-brown spots may also appear, usually on parts of the plant that are dying. Where formerly resistant lines of wheat are becoming susceptible, symptoms can include small brown spots or small pustules which may have a pale green or yellow halo.

Organism

Puccinia triticina (exotic strains)

Host range

Wheat, specially bread (Triticum aestivum), durum (T. durum) and Triticale.

Method of spread

The spores can be carried several hundred kilometres by the wind, and local spread may also be possible via contaminated clothes and equipment.

Conditions favouring disease

Infection is favoured by wet leaves and a temperature of about 20°C for at least four hours. Also favouring disease is a build-up of spores that survived from the previous season or were produced from self-sown hosts.

Confused with?

Other rust fungi. Also, other pathogens (e.g. Alternaria triticina), nutritional disorders and some chemical burns may produce light coloured spots, however these cannot be rubbed off. Rust pustules can be largely removed by rubbing and they also stain the fingers brown-orange.

Where?

The fungus causing leaf rust is found around the world, including Victoria. Exotic strains of the fungus are of potential concern to us.