Growers of oilseed rape varieties with inherently high disease resistance, for Phoma stem canker, Verticillium and Light Leaf Spot, will be reassured of getting the best from that variety and be assured of increased flexibility on timings when they do have to use fungicides.
“It looks as if it will be a high risk year for quite a few different diseases in winter oilseed rape. The wet summer, later drillings and now smaller plants all add up to a high risk scenario for Phoma Stem canker. Most areas have had the necessary 20 days of rainfall after the 1st of August to trigger this disease and there are many highly susceptible varieties, in particular the hybrids. Looking at today’s HGCA Listings, of the 18 varieties which have the lowest resistance ratings of 4 or 5, thirteen are hybrids including varieties such as PR46W21, PR45D06, PR45D03, Excalibur, all of which have the lowest rating of just 4. DK Cabernet and Sesame have a rating of only 5 for Phoma,” points Neil Groom, Technical Director of Grainseed Ltd.
“All four conventional varieties from Grainseed, Es Astrid, Es Alienor, Es Agatha and Es Cubic, have excellent disease ratings against Phoma of 7 and as such will be easier and cheaper to manage, with the need for fungicide reduced. Such resistant varieties appear to withstand the disease for longer, allowing greater timing flexibility of your fungicide. Phoma stem canker is capable of eroding yields by at least 0.5 t/ha, which is worth £185/ha at today’s prices. If the disease gets hold in a small crop as it could easily do this autumn in susceptible varieties, it can cause even more significant damage, including premature death of individual plants within the crop,” he points out.
“The basis of Phoma resistance in the three low biomass varieties Astrid, Agatha and Cubic is multigenic and is long lasting. They also have a good Light Leaf Spot resistance of 5, which gives a sound base to the combined disease resistance. In the East/West HGCA listing, 11 varieties had a 5 rating, 12 had a 6 rating, one had a 7 and one had a 9 rating for Light Leaf Spot,” reports Neil.
“When it comes to another damaging disease Verticillium, it too is expected to be at higher levels this year, following on from a high disease incidence last year. But there are no proven chemical solutions that can be fallen back upon. The only practical way to reduce its impact is to grow resistant varieties as well as you can, particularly as the pathogen can survive in soil for over ten years.”
Grainseed have a very strong portfolio of Verticillium resistant rape varieties including Alienor, Agatha and Cubic. “Research at ADAS Boxworth this year showed Alienor giving phenomenally good resistance to this damaging disease. Agatha and Cubic showed the same high level of resistance as Catana, which to date has been regarded as the control variety.”
Neil reports that other screening work in the UK and France showed Alienor and Agatha able to resist Verticillium well, much better than varieties such as Castille and Excalibur that were very badly affected. “Dr. Peter Gladders of ADAS has warned that growing susceptible varieties too widely will lead to a build up of Verticillium in the soil. Conversely, growing resistant varieties should help reduce the pathogen in the soil over the years.”
“Proactively using varietal resistance in oilseed rape as part of an integrated plan can only help to manage disease better. Growers who have already chosen to grow the Phoma resistant Astrid, Alienor, Agatha and Cubic and Verticillium resistant Alienor, Agatha and Cubic can be reassured that they will have a much easier job on their hands. With high disease pressure expected this year plus continuing positive economics of growing rape, an integrated approach to disease management makes good sense in oilseed rape,” concludes Neil Groom.