Light leaf spot can cause substantial yield losses warns Craig Padley of breeder LSPB (LS Plant Breeding). Figures published by Rothamsted show these can add up to 1.5 t/ha, at an estimated cost of more than £15-30 million in the UK1. This is despite significant expenditure on fungicide to control the disease.
"Cracker has been a dependable mainstay variety for oilseed rape growers – especially those in Scotland – faced with the threat of Clubroot and Light leaf spot. Our latest monitoring shows that, while the variety's Clubroot benefit remains, it has resistance rather than immunity to Light leaf spot. In most areas, Cracker will still exhibit reasonable resistance, but this should not be relied upon – and the crop should be regularly checked as for a susceptible type and sprayed as necessary.
"However, growers do now have an alternative – the HGCA Candidate variety Mentor – which has improved yield plus a higher level of background resistance (or quantitative resistance) to Light leaf spot than Cracker. It will still need spraying, but now that the major gene resistance in Cracker is no longer effective, especially in the north east, Mentor could be the better option.
"The point to stress here is that if you are going to have to spray for Light leaf spot anyway, you can now go for the higher yield of Clubroot resistant Mentor.'
Mr Padley adds that there is also a third choice for growers: "If it is Light leaf spot resistance you are after, then you can grow Marble, a semi dwarf HGCA Candidate variety with good resistance across all sites. And the two year yield data for Marble shows excellent yields – particularly in the north.'