Brown rust in cereals

Brown rust affects both wheat and barley. However, exploitation of varietal disease resistance, adoption of cultural control techniques and timely treatment of crops with fungicides all help to reduce disease pressure.

Note: Also known as leaf rust.

Brown rust affects both wheat and barley crops.

There is large seasonal and geographic variation in brown rust severity. Cold winters may reduce its spread. Climate change is leading to milder winters and higher than normal spring temperatures. Consequently, brown rust levels are now higher earlier in the spring and found in new locations (e.g. further North).

Brown rust in wheat is common in Southern and Eastern parts of the UK, which have higher summer temperatures than other regions. Brown rust tends to develop later in the summer than yellow rust and results in a significant loss of green leaf area and, hence, yield and specific weight.

Brown rust in barley can be widespread, if conditions are conducive and there is dense cropping of barley. Brown rust epidemics on barley tend to start earlier in the spring than for wheat. Brown rust is usually more of an issue in winter barley than in spring barley, especially in early sown crops when the winter is mild. A severe attack of brown rust early in the season impacts on final yield, through reduced green leaf area and tiller retention.

Orange-to-brown colour pustules (about 0.5–1.0 mm in diameter) often develop in the autumn on early-sown crops. In early infections, pustules are frequently confused with yellow rust. There is greater differentiation of colour later in the season. Additionally, brown rust pustules tend to be scattered at random, compared with the more striped symptoms of yellow rust. Often seen on the leaves, symptoms can occur on the stem, leaf sheaths, and ears when infection is severe. When leaves begin to senesce, a 'green island' develops around individual pustules. Dark teliospores may be produced towards the end of the season.

Puccinia triticina is specific to wheat. Other Puccinia spp. and pathotypes affect barley, rye and triticale but do not cross-infect.

• Puccinia triticina (formerly known as Puccinia recondita f. sp. tritici) – wheat
• Puccinia hordei – barley
• Puccinia recondita – rye, triticale

The fungus can only grow and survive on live leaf tissue. It overwinters mainly on volunteers and early drilled crops. It spreads by airborne spores. Dark teliospores may develop on diseased plant tissue, indicating a second developmental stage of the fungus.

Temperatures between 15°C and 22°C are optimal for sporulation and germination. However, the disease is active between 7°C and 25°C (a wider temperature range than for yellow rust). Surface moisture on leaves (i.e. 100% relative humidity) is essential for spore germination. Consequently, brown rust epidemics in UK wheat crops normally occur during mid-to-late summer. At this time, windy days disperse spores and cool nights with dew favour the build-up of the disease. Symptoms can occur 5–6 days after infection at optimum temperatures. Cold weather slows disease development but does not kill the pathogen (unless the leaf dies).

Barley tends to suffer from brown rust infection earlier in the spring than wheat. In both crops, rapid spread can occur in warm weather later in the season.

Alternative host species exists for P. triticina but their role is not significant in the UK.

• Susceptible varieties
• Early drilling
• Mild winter
• Hot, humid weather, especially in April to July
• Southern regions of the UK
• Volunteers that provide a green bridge. Note: wheat volunteers are not a risk to barley and vice versa

Varietal resistance offers an effective method to manage brown rust in both wheat and barley. AHDB Recommended Lists (RL) brown rust ratings reflect the resistance of adult plants during the main part of the growing season (from about stem extension onwards). Resistance ratings do not provide any guarantee of durability of resistance, as the pathogen population can change, and new rust races can develop to overcome these resistances. Therefore, monitor all varieties regularly for symptoms.

Based on RL trial results, the wheat brown rust watch list can reveal varieties that performed out of line with their RL disease resistance rating at some sites. The list also indicates varieties with a low anticipated level of young plant resistance. Almost all wheat varieties are susceptible to brown rust at the young plant stage. Use the list to help understand disease risk and focus in-season management.

Destruction of volunteers helps to prevent disease carry-over of the disease, as they act as a green bridge from one season to another. Wheat volunteers do not pose a brown rust risk for barley (and vice versa), since the different pathotypes do not cross infect. Delaying drilling of susceptible varieties can reduce risk. Managing nitrogen to avoid excessive concentrations in plants (e.g. from late doses of nitrogen) can also help.

Fungicides

Systemic seed treatments may help delay epidemics developing where risk is high. However, seed treatments are likely to provide less control of brown rust than yellow rust. Using fungicides to protect against infection is far more successful than eradicating established disease.

• Grow a variety with a high resistance rating, but monitor disease levels throughout the season
• Eradicate volunteers to remove green bridge
• Delay drilling of susceptible varieties
• Manage nitrogen applications to avoid excessive concentrations in plants
• In wheat, apply a fungicide with activity against brown rust when the disease is seen and conditions are conducive or at T2 and T3 in high-risk situations
• In barley, use fungicides early to control the disease. However, the azole/SDHI mixes used on other barley diseases will usually provide sufficient control