Cold winter ‘only delays yellow rust’

Cereal growers are being urged not to underestimate the threat which yellow rust will pose during 2010 – despite the coldest winter for 30 years.

The big freeze might have delayed the yellow rust threat but it has not reduced the potential for the disease to develop over the coming weeks, according to Paul Fenwick of plant pathologist with Nickerson Seeds.

“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,” said 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 even the UK’s worst conditions for decades would do little to diminish its impact, said Mr Fenwick. Under snow, plant temperatures may not have dipped much below 0°C, he added.

Snow insulated any sporulating lesions from the cold, so even air temperatures below -4°C would fail to eliminate yellow rust lesions which were present and these would 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.”

“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.”

Infection could take place at temperatures above 0°C, so growers who had drilled susceptible varieties should remain vigilant and monitor crops carefully to ensure that they applied the most appropriate fungicide.

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