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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.
Yellow rust 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 development of yellow rust in regions of the UK can be seen using the AHDB disease monitoring tools at: http://cereals.ahdb.org.uk/monitoring/disease-moni...
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.
The UK Cereal Pathogen Virulence Survey (UKCPVS) has found a new race of wheat yellow rust – the ‘Kranich’ race. Some current varieties are partially susceptible to it so it is suggested that growers monitor winter wheat, including varieties with a high disease rating, and report unexpected outbreaks of yellow rust to the UKCPVS – further information: http://cereals.ahdb.org.uk/press/2016/february/10/%E2%80%98kranich%E2%80%99-yellow-rust-race-detected-in-the-uk-for-the-first-time.aspx
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.
Information on current fungicide efficacy is available from the AHDB – see: http://cereals.ahdb.org.uk/med...
Generally, Azoles, SDHI, strobilurins and morpholines are recommended, used as mixtures, as protectants 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. Although recent changes to the pathogen population has reduced the efficacy of resistance in many varieties and made it impossible to alternate varieties that are completely resistant to certain races, it is still advised to grow a range of 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.
Please note that there have recently been major revisions to wheat yellow rust disease ratings due to emergence of new virulent races of yellow rust. Please see p. 3 of the AHDB Recommended list. Varieties with the best yellow rust resistance (rating of 9) in the 2017/18 list are 'KWS Trinity', 'RGT Illustrious' and 'Crusoe' in nabim group 1; 'KWS Siskin' in nabim group 2; 'Revelation', 'LG Sundance and 'LG Motown' in nabim group 4.
As pathogen populations are diverse and can change rapidly, so can resistance status. It is important that crops are monitored regularly and unexpected disease observations reported to UKCPVS.
- AHDB disease monitoring
- Fungicide activity and performance in wheat
- UK Cereal Pathogen Virulence Survey – Yellow rust of wheat
- Wheat Yellow Rust Genomics
- AHDB Recommended list
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Kranich... The name of the new yellow rust race found in the UK https://t.co/9mxYEScSRm— Caroline Nicholls (@AgriCaroline) February 10, 2016