First symptoms appear during the late winter to spring as small, circular, orange-brown pustules scattered at random on the upper side of leaves. These contain the spores that will give rise to the infectious process between barley plants. Occasionally these pustules also develop on the stems, leaf sheaths and ears. A yellow or green halo often surrounds them. Later in the season (late spring or early summer) small black pustules gradually develop on the underside of the leaves. These new sacs contain the spores that will later survive on crop tillers or alternate hosts to restart the cycle. Contrary to the light brown pustules, the black ones do not rub off onto the fingers when rubbed.
The symptoms are caused by the fungus Puccinia hordei, one of the four types of fungi that trigger rust in barley. These organisms can only grow on green plants. In the case of P. hordei, it survives the summer on late tillers and alternate hosts such as the Star of Bethlehem (Ornithogalum umbellatum). Warm temperatures (15° to 22°C) with high humidity and frequent rainfalls favor disease development, while dry windy days aid the spreads of the spores. Severe attacks of brown rust in barley occur mainly in late season, particularly if high doses of nitrogen have been applied. Crops sown early are more severely infected than those sown later, particularly when nights are still warm. However, brown rust in barley is rarely a problem if crops are treated with a fungicide.
To date, no biological control solution for brown rust of barley is available. Please contact us if you know of any.
Always consider an integrated approach with preventive measures and biological treatments if available. A timely spray with protectant fungicides based on prothioconazole will generally help to control brown rust. There is also a range of foliar fungicides available to treat leaf rust in barley. For the best suppression, apply them when leaf rust is first detected. Additional applications may be necessary when the season is favorable for rust diseases.