All change again for yellow rust?

Planting varieties of wheat with a robust resistance to yellow rust can allow for reduced fungicide inputs and avoid the need for early TØ  sprays to the crop.

Planting varieties of wheat with a robust degree of resistance to yellow rust can allow for reduced fungicide inputs and avoid the need for early TØ sprays to the crop but yellow rust races often adjust rapidly so ratings can change quickly within a season, which seems to have been the case in 2019.

The ratings given in variety tables are UK averages but trial results from 2019 show quite large differences in how well varieties stood up to yellow rust between different sites. The UK’s Cereal Pathogen Virulence survey is collating results of tests from this season and will present the shift in races at this year’s stakeholder meetings after Christmas, but indications from a major RustWatch project in Europe confirm there are some new races in play.

Varieties such as LG Skyscraper (rated 8), Elation (9) LG Sundance (9) and Barrel (9) all carry good ratings – as do almost all the varieties on the Scottish Recommended list with the exception of Zulu, which is, rated 5. But concerns over higher than expected levels of yellow rust on some previously resistant varieties like Elicit (9) and KWS Lili (7) need to be taken seriously.

The risk of yellow rust next season will largely depend on the severity of the winter. We have had had brief spells of cold weather which will help reduce the risk but to date, there hasn’t been sustained cold to eradicate the disease, although to date any UK reports to date are reassuringly far south around Cambridgeshire.

It is still likely that T0 sprays on wheat can be avoided in 2020 but the advice is to walk all wheat crops regularly, particularly the early drilled ones which are at the highest risk and watch for reports of the disease in Scotland as crops start to grow away in the spring. Where yellow rust appears in crops the early use of azole fungicides might be necessary, but the ideal scenario is that any yellow rust reports are sufficiently late that routine fungicide programmes in wheat starting at leaf 3 emerged have already been applied.

Fiona Burnett, SRUC, for the Farm Advisory Service