Yellow rust is a disease caused by the pathogen, Puccinia striiformis. It can be found in wheat, barley, and triticale. There are distinct forms of the pathogen which are specific to different crops, meaning cross-contamination between barley and wheat, for example, is unlikely. Within the different forms of P. striiformis, there are different races which only affect certain varieties.
Symptoms appear as parallel rows of yellowish orange coloured pustules on the leaves of the plants. Generally, the disease over-winters, with symptoms missed until the early spring when patches of infected plants can be seen in fields. The symptoms can be confused with brown rust, as the colour can be similar, but whereas the pustules appear randomly on the leaf with brown rust, with yellow rust they are usually in very clear lines. It is for this reason that sometimes yellow rust is known as “stripe rust”.
Severe epidemics are often associated with more susceptible varieties, mild winters, and cool, moist summers. Yield losses of 40-50% have been recorded in these situations.