Clubroot is an increasing problem in oilseed rape crops throughout the UK, exacerbated by too-close rotations.

But, it is even more of an issue in Scotland, where mixed farming plus high rainfall increased the risk.

“Yield losses can be substantial – over 50% of potential in affected crops – and severe infections can even lead to the crop being abandoned,” said Craig Padley, head of oilseed and pulse breeding with LS Plant Breeding (LSPB).

“Key symptoms are wilted or stunted plants in hot, dry weather as the galls on roots formed by the clubroot pathogen affect normal root function, reducing water and nutrient uptake,” he pointed out.

“Large root galls on the taproot mean root function is seriously impaired. As the gall decays, spores are released back into the soil where they can persist in soils for at least 15 years.”

Growers in at-risk areas should investigate patches of poor growth at this time of year and regard it as routine to get soils tested for clubroot and pH, using the results to plan their strategy.

Rotations of growing OSR one year in five or more is best practice, he said, pointing out that LSPB’s Mentor remains the only variety on the 2017/8 AHDB Recommended List resistant to common strains of clubroot.

It has a ‘specific recommendation’ – and it is the latest in a line of resistant varieties from LSPB, with further new varieties under trial.

Mentor is a medium-early maturing variety with good seed yield combined with high oil content to give high gross output. But it may, however, be infected by some strains and infections that have been reported in some fields, so over-reliance in close rotations should still be avoided, he said.