Yellow Rust

Puccinica striiformis

Pathogen

Fungus

Hosts

Wheat, barley.

Symptoms

The first yellow pustules usually appear at the apex of the leaves. These develop into symmetrical `stripe` lesions along the leaf, bearing orange-yellow pustules. These are located just underneath the upper leaf layer (epidermis), and are much less compact than brown rust pustules. Glumes, awns and grains can also be infected.

Development

Rust fungi can only grow on green plant tissue and the harvest period is survived on tillers and volunteers. Spread to autumn sown plants is via windborne spores. It originates as distinct `foci` in crops and is then dispersed over long distances. Whilst young plants are susceptible, as they mature, they can develop `adult plant resistance`.

Favourable Factors

The ideal growth conditions for yellow rust are temperatures of between 8 – 13°C for spore germination and penetration and 12 – 15°C for further development. Late applications of nitrogen tend to favour the disease. Epidemics can occur very rapidly with severe infection developing within a week. High temperatures (above 20°C) will check an epidemic.

Importance

This disease is prominent in coastal regions with cool summers and frequent mists, especially Eastern counties and susceptible varieties with a low recommended list disease rating.

Yield losses can range from 5 % to as high as 30 % in severe, uncontrolled epidemics. These penalties result from rust colonies in the leaf draining carbohydrate from the plant and reducing green leaf area. Severe infections result in poor root growth and drought susceptibility and grain becomes shrivelled and germination (if a seed crop) may be impaired.

Control