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.
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`.
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.
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.
• Varietal tolerance
• Disposal of crop debris and volunteers
• Seed treatments with activity on yellow rust
• Use of an effective fungicide programme.
Find out more information on the key disease threats to your cereal crop. For each disease you will find out the importance of the disease in terms of potential yield penalty, how to identify the disease in its early stages and our advice on the best control strategies.