Phoma stem canker is still the most significant and costly disease of oilseed rape and, with increasing pressure on margins in oilseed rape, growers should be selecting their rape varieties with multigene resistance to this disease and saving on expensive fungicides.

“There has been a lot of concern about Light Leaf spot in recent years, but it is important we don’t lose sight of Phoma stem canker, which remains the biggest threat to rape in England, particularly in the South and East. The HGCA Crop Monitor registers Phoma leaf spotting last year affecting 100 per cent of crops in the SouthEast, 95 per cent of crops in the East, 90 per cent in the SouthWest and 89 per cent in the Midlands and West. Even in the North, over 75 per cent of crops had Phoma. This disease can cause premature death of the plant and yield losses up to 50 per cent. Where control is lacking, losses of between 0.5 and 1 t/ha are common,” said Neil Groom, Technical Director of Grainseed.

Neil said that growers need to be looking more carefully at resistance ratings for stem canker when selecting varieties for this coming year. “If you look at the past ten years of the HGCA variety listing, the overall trend is for more varieties with poorer Phoma ratings. The analysis shows more varieties with a 4 rating (in 2015/16 there were 31 per cent varieties with this rating, whereas in 2006/07 19 per cent had a 4) and more with just a 3 rating (12 per cent in 2015/16 and none in 2006/07).”

Neil thinks that it is concerning that fewer varieties have good resistance rating to the most damaging disease of rape. “There should be a stronger focus on durable disease resistance in the future. In Grainseed our breeders select out varieties with good resistance to Phoma as a priority – for example Astrid has 7.0 rating for Phoma, Alienor has 7.4, Alegria 7.0 and the new variety Mambo 7.8. These varieties all have multigene resistance so this won’t break down in the field. Experts calculate each rating point against Phoma stem canker is worth at least £20/ha.”

Neil also mentions significant work being done by plant pathologist Dr Bruce Fitt at the University of Hertfordshire. “It appears the problem is only likely to get worse. Applying climate change models to current disease population modelling, Dr Fitt predicts that Phoma stem canker epidemics will not only increase in severity but also spread northwards to Scotland by the 2020s and that yield losses will increase to 50 per cent in southern England if disease is not controlled. So Phoma is likely to become even more significant a disease.”

“Our three winter oilseed rape varieties Es Alienor, Es Alegria and Es Mambo are all conventional types and all have clearly strong autumn vigour, both in trials and in the field – as good as or even better than the hybrids. Being conventionals, you can drill at a good seed rate to make sure the crop establishes well and grows away from Cabbage Stem Flea beetle attacks. And you are able save your own seed. Growers need to be looking at different and varied ways of growing robust varieties that can stand up to disease and pest attack whilst saving on inputs,” said Neil Groom.