Cereal growers should not under-estimate the threat which yellow rust will pose during 2010 or believe that the recent spell of cold weather in the UK, however severe, has reduced the potential for the disease to develop over the coming weeks, according to Nickerson’s Paul Fenwick, one of the UK’s leading plant pathologists.

“The danger is that growers will assume that the exceptionally low temperatures which have been experienced throughout the country this winter have eliminated the threat from yellow rust,” emphasises Mr Fenwick. “That is most definitely not the case, especially with more susceptible varieties, bearing in mind that 40% of the crop, based on seed certifications, is in varieties rated 4 or less for yellow rust. The cold weather might have delayed the onset of yellow rust, but the disease is still present in UK crops. Signs of it may not become apparent as early as they might in a normal year, but will certainly become evident once temperatures begin to rise.

“Yellow rust can survive even harsh Canadian winters, so the UK’s worst conditions for 18 years will do little to diminish its overall impact this season. Despite the fact that overnight air temperatures have fallen to very low levels in some parts of the country, under a thick blanket of snow the actual temperature experienced by the plant may not have dipped much below 0°C. Snow insulates any sporulating lesions from the cold, so even air temperatures below -4°C will fail to eliminate yellow rust lesions which are present and these will merely be held in suspended animation. If the plant is growing and the leaves remain green, which they will have done if yellow rust infection has remained at a sub-clinical level and fungal growth has been contained within the leaf, the threat from the disease remains.

“Regardless of the weather which we experience during the remainder of this winter, and there is still some way to go, the high proportion of susceptible varieties currently in the ground provides the potential for an explosion of yellow rust this spring. Even if conditions remain cold during February, March and April this will merely slow down the onset of the disease, not eliminate the threat. But if we have a mild February, then growers will have to act fast to stay on top of yellow rust.

“It is too early to say exactly what overall effect the cold weather will have on the incidence of yellow rust this season. However, whilst it has reduced the opportunity to go through early generations of the disease, the onset of yellow rust in susceptible varieties has merely been delayed until warmer weather arrives, as there could be months between infection and sporulation. Infection can take place at temperatures above 0°C, so growers who have drilled susceptible varieties must remain vigilant and monitor crops very carefully to ensure that they apply the most appropriate fungicide.”

Looking ahead, Mr Fenwick advises growers to consider HGCA Recommended List yellow rust ratings very carefully and minimise the cost of controlling this yield-sapping disease by selecting varieties with a high level of genetic resistance. He states:

“The resurgence of yellow rust in winter wheat crops last season included a new, aggressive race which is affecting several high-profile varieties. Growers should therefore carefully consider the revised Recommended List resistance ratings, which reflect Nickerson’s own disease trials for yellow rust and provide a true reflection of current varietal resistance.

“Nine of the 15 varieties which the HGCA rates as being ‘highly resistant’ (8 or 9) to yellow rust come from the Nickerson stable. They include Claire, which after 10 years on the Recommended List is still highly resistant to the disease, together with Alchemy, Cassius, Istabraq, Panorama, Xi19, Zebedee, Invicta and Edmunds.”

FOR FURTHER PRESS INFORMATION PLEASE CONTACT:
• Laura Davey, Nickerson on 01472 370151
• Julian Cooksley, Kendalls Communications on 01394 610022