Appearance, impact and biology

On leaves of young plants, discrete individual yellow pustules of spores <1mm in diameter occur but on adult plants, these elongate into larger stripes of chlorosis and yellow sporulation. In fields, initial foci of the disease can establish over winter and in untreated crops will expand in the spring, rapidly spreading to the entire field if left untreated.

This can reduce yields by 50% on untreated crops due to reduced green leaf area and enhanced water-loss from diseased leaves.

The fungus arrives as airborne spores in the autumn and can over-winter but spreads again as wind dispersed spores in the spring. Epidemics are encouraged by repeated periods of dry sunny days, followed by cool nights with dew on leaves in the spring as these are ideal conditions for sporulation, dispersal and infection.

Generally, yellow rust is most severe in eastern counties of the UK. Current news on development of new races of yellow rust in regions of the UK can be seen using the AHDB UKCPVS site.

New races of the pathogen have arrived in Europe from parts of Asia in the past few years. In addition, some strains are able to tolerate warmer conditions than previously.

Early vigilance is advised, particularly on susceptible varieties because epidemics can take-off as early as March, with a T0 spray application advised in these cases.


Fungicide choice

Information on current fungicide efficacy is available from the AHDB – see page 11. And in this information from NIAB.

Generally, Azoles (DMIs; e.g. prothioconazole) should be used at full label dose and mixed with other modes of action such as, SDHI (e.g. bixafen), strobilurins (e.g. pyraclostrobin) and morpholines (e.g. Fepropimorph) or spiroketalmines (e.g. spiroxamine) and are best used as protectants or at early stages of infection against yellow rust.

Other control options

Diversification of varieties is advised so that not all varieties grown on a farm will be susceptible to the same races. There are currently several varieties that are resistant to yellow rust and it is still advised to grow a range of different varieties. Juvenile plant resistance (up to stem elongation) may be different to that of adult plant resistance. The AHDB Recommended List provides information only on the resistance of adult plants, as this is the most important stage for growers. For more detailed information on varietal resistance, see: https://ahdb.org.uk/ukcpvs or more generally, see the Recommended List resistance ratings – page 10 and 11.

Related links