Farming News - Yellow Rust - what is the risk after the coldest winter in 30 years
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Yellow Rust - what is the risk after the coldest winter in 30 years
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Danish work:
Disease severity of wheat yellow rust, Puccinia striiformis f.sp. tritici, was analysed in Denmark from 1985 to 1999 in relation to the effects of weather on winter survival, distribution of host cultivars and pathotype dynamics. Below-average temperatures in January and February (midwinter) reduced yellow rust on the susceptible cv. Anja, and in three of four growth seasons following cold winters no yellow rust was observed on any cultivar under natural conditions.
Canadian work:
Temperature is the major factor effecting the winter survival of the pathogen of stripe rust. Rapilly (1979) considered that temperatures below –10 °C might halt the pathogen development. Cold-weather conditions reduce the pathogen winter survival by winter killing the pathogen in the infected leaves. Therefore, temperature is one of the major weather factors used to predict occurrence of stripe rust.
UK work:
And Neil Paveley from a High Mothorpe Q&A on yellow rust risk in 1999. “The high levels of yellow rust this season make carry-over of disease to next year more likely. However, a period of cold frosts, below -5C would kill many of the infections and reduce the risk.” This was confirmed from research published in the Annals of Applied Biology in 2007, this UK research concluded that the percentage of crops with yellow rust decreased with cultivar disease resistance ratings ≥3 and the occurrence of severe frosts (<−5°C)". The percentage of crops affected by yellow rust was reduced from 19.2% with no frost to 6.1% with one to five frosts and 1.3–1.9% with greater than five frosts.
Low winter temperatures have been identified as a significant factor in the seasonal variation in epidemic development. Criteria based on low temperatures during the period November to March or December to April were as effective as the number of frost days in indicating seasonal risk. The mechanism involved may be a reduction in the number of disease cycles that can be completed during the winter and hence reduced survival through prevention of infection of new leaves as old infected leaves senesce. A quick run through the temperature records for the weather stations around the UK reveals that there were at least 3 nights in both December and January when temperatures fell to -5 or less. In some places it was considerably lower. The Met office recorded -11.8 in Oxfordshire and -10.8 in Hampshire.
Taking all this into account you really have to wonder if the threat of a Yellow Rust epidemic this year exists at all.
NIAB comment.
Rosemary Bayles of NIAB says we still have a lot to learn about Yellow rust. Yellow rust only survives in green leaf tissue so if any infected leaves have been killed off by the frost then that will have reduced the risk. The cold winter has definitely delayed the start of any epidemic by four to six weeks and as such reduced the the risk status to "fairly normal" but, she cautions, the risk is still there.
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