Brown Rust [Puccinia recondita]

Plant species specific disease that overwinters as a mycelium on volunteer cereals or winter cereals. The spores are spread with the wind. Mild fall and winter weather, a warm spring and high nitrogen fertilization are favorable for the pathogen. The epidemic spread often takes place only after ear emergence. Brown rust may also goes through a full development cycle with core phases with meadow-rue as an alternate host, although this is insignificant under Central European growing conditions. Triticale, is less prone to significant yield losses even with high infection rates.

Pest Profile

About the pest

Hosts

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

Symptoms & Diagnosis

Pattern of damage

Symptoms of brown rust infection are often seen in the autumn on early-sown crops as individual orange to brown pustules. With early autumn infection individual pustules can be confused with yellow rust, being orange to brown in colour and about 0.5-1.0 mm in diameter. Later in the season, diagnosis is much easier as the brown pustules tend to be scattered at random compared with the more striped symptoms of yellow rust (Puccinia striiformis). Although symptoms are most common on leaves, in severe attacks pustules can also occur on the stem and glumes. Brown rust infection of the glumes can result in a reduction in specific weight. When leaves begin to senesce, a 'green island' develops around individual pustules. Towards the end of the season dark teliospores are sometimes produced.

Life cycle

The fungus over-winters primarily on volunteers and early-drilled crops. The alternate hosts for P. triticina include species of Thalictrum, Isopyrum and Clematis, although their role in the life cycle in the UK is not thought to be significant. Until recently the disease was rarely important in the spring as temperatures between 15°C and 22°C, accompanied by 100% relative humidity, are needed for sporulation and spore germination. Consequently, brown rust epidemics have normally occurred during mid to late summer in the UK with dry windy days which disperse spores, and cool nights with dew, favouring the build-up of the disease. However, with mild winters, brown rust can often be found at high levels in the spring. With climate change mild winters and warm springs are likely to become more common which could lead to brown rust becoming a much more common problem earlier in the season.

Remarks

Until recently brown rust was not considered to be a major problem despite early-sown crops generally carrying high levels of brown rust through the winter. However, the occurrence of new virulent strains overcoming varietal resistance in a few key wheat varieties has moved brown rust up the league table of importance. Severe attacks result in a significant loss of green leaf area and hence yield, infection of the ears will also result in loss of grain quality. It is too soon to predict epidemic levels of brown rust in future seasons but it is now a disease that cannot be ignored.