UK oilseed rape growers are increasingly aware of clubroot as a threat to their crops. Driven by too-close rotations, the disease is no longer a problem only in Scotland and the Borders - where previous mixed farming plus high rainfall increases the risk - but is now seen in England.
“Clubroot can cause yield losses of 50% of potential - or even crop loss with severe infections. And while the problem is perceived to be an issue for Scotland and the Borders, in reality clubroot has now become an issue in the wetter parts of the rest of England as well,” warns Theo Labuda, Managing Director of LS Plant Breeding Ltd (LSPB).
He advises that growers in at-risk areas should investigate patches of poor growth and regard it as routine to get soils tested for clubroot and pH. Warning signs are wilted or stunted plants in hot, dry weather. The large galls on roots formed by the clubroot pathogen, Plasmodiophora brassicae, affect normal root function, reducing water and nutrient uptake. Then as the gall decays, spores are released back into the soil where they can persist for 15-20 years.
As general good practice, well-spaced rotations of oilseed rape, cereals and pulses should be standard practice - with oilseed rape one year in five or more as optimal.
Varietal choice should also be an important part of growers' clubroot armoury, with Mentor as the only variety on the 2017/8 AHDB Recommended List of winter oilseed rape for both the East/West and North regions with a ‘Specific Recommendation’.
Mentor is resistant to common strains of clubroot and is a medium-early maturing variety with good seed yield combined with high oil content to give high gross output. Agronomic characters are that it has good stem stiffness and resistance to lodging and is of medium height.
Mentor may, however, be infected by some strains and infections that have been reported in some fields, so over-reliance in close rotations should be avoided.
There is now further progress on the varietal front with LSPB’s Crome currently progressing through official trials as a UK Recommended List candidate this year, to be commercially available for 2019 drilling.
Crome has a higher seed yield than Mentor, and its increased oil content of 46.7% brings a very worthwhile 3.7% higher gross output based on trials to date. Agronomic characters are also better with boost to LLS resistance rating from 5.7 to 6.3.
“A number of varieties have passed through trials over recent years but have fallen by the wayside. With Cracker previously, followed by Mentor - and now Crome for the future - we are giving growers a worthwhile addition to their armoury against yield-sapping clubroot to add to the equally important strategy of well-spaced rotations of oilseed rape,” adds Mr Labuda.