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Cereal yellow rust, or stripe rust, is a fungal disease that occurs mainly after mild winters and cool, damp weather in spring. Infestation is recognizable by the yellow pustules arranged in stripes, which are formed along infested leaves.

Biology

Yellow rust belongs to the stand fungi (Basidiomycota) and is an obligate parasite. This means that it requires surviving host plants throughout the year in order to survive. It has an incomplete development cycle because it does not produce all spore forms. When an infestation occurs, so-called running hyphae are formed inside the leaf along the leaf veins for rapid dispersal and numerous spore deposits are formed, which appear as rust spore pustules arranged in stripes. This is why yellow rust has also been given the name stripe rust.

Host plants

Yellow rust mainly attacks winter wheat, winter triticale, winter durum and spelt, as well as barley. Rye is much less affected and to a lesser extent. Yellow rust can also occur on numerous grass species.

Distribution

Yellow rust prefers cool, humid climates in northwestern Europe, but also occurs in wetter and higher-altitude cereal-growing areas. If susceptible varieties are grown in dry areas, however, it can also cause yield losses there.

Propagation and transmission

Yellow rust survives the winter on volunteer and winter cereals by means of spores (uredospores) and/or as mycelium. In frost the spores die, in severe winters also the fungal mycelium.

A special feature of yellow rust is that the uredospores are embedded in thin mucilage substances in their spore stores. In spring, therefore, wind and rain increasingly transport spore packages rather than individual spores. If a spore gets onto a host plant, liquid water must be present for it to germinate. Infections can occur as early as 0 °C. The fungal spores germinate in a film of water in darkness and penetrate their host plants through stomata. Even relatively few spores are sufficient to cause severe infections. The risk of an epidemic is greatest at 10 to 15 °C, high humidity and high light intensity. However, a yellow rust epidemic can also continue to develop during very warm to hot weather periods. However, for this to happen, dew must form at night and temperatures must fall below 15 °C.

The best conditions for the risk of a yellow rust epidemic are: Failure cereals become infected in the fall, early sowing of winter cereals, mild winters or a protective snow cover, damp-cool weather in the spring, cultivation of susceptible varieties, and a high nitrogen supply to the soil.

Economic importance

Yield losses of up to 50% are possible. Economically, yellow rust is mainly of importance in wheat.

Prevention and control

• Preventive careful removal of volunteer cereals.
• Avoid cultivation of winter crops too early
• As far as possible, spatial separation of fall and spring sowings of the same cereal variety
• Cultivation of less susceptible varieties
• Possibly also use of plant protection products (see list of plant protection products approved in Austria)

Specialized information

Yellow rust epidemics occur when a new breed appears in the already complex breed mixture, either through mutation or sexual recombination. In Austria, this was the case from 1998 to 2001 and has also been observed since 2013. For this reason, varietal resistance also does not remain stable in some cases. Therefore, regular monitoring of the stocks is recommended even for varieties described as more resistant. When new races appear, they are included in the race mixture for the tests of specific variety resistance in the following year.

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