Top disease rated oilseed rape varieties needed to help crops off to a good start

With the early establishment phase being so critical to the overall success of the oilseed rape crop, sowing a disease resistant variety such as Es Astrid or Es Alienor will give young seedlings the best opportunity to survive against Phoma this autumn, according to Grainseed.

Neil Groom, Technical Manager of Grainseed, explains that the scene looks set for another high risk year for Phoma. "The most important source of infection for newly emerged crops is air-borne spores from oilseed rape stubble after harvest. Just 20 days of rain from the 1st of August are needed to trigger the release of these air-borne spores that then infect newly-emerged oilseed rape plants to produce leaf spots - a threshold that may well have been reached in many parts of the country already. If the current weather pattern continues, it will be another high risk Phoma year. This is particularly concerning as the damaging effects of Phoma are more serious in smaller plants. The fungus has to grow a shorter distance down the leaf petiole to reach the stem base where it forms cankers. By growing a resistant rape variety such as Astrid or Alienor, plants are protected from this early, very damaging attack."

He reports that these two conventional low biomass varieties have the highest ratings when it comes to Phoma resistance. "Astrid has a Phoma disease rating of 7.0 whilst Es Alienor has a rating of 7.4, well above all other conventional varieties. Castile has a 5.8 rating for Phoma, whilst NKBravour has 5.0, Lioness 4.8, NKGrace 4.7, Flash 4.5 and Catana 4.4."

The Phoma resistance in both Astrid and Alienor is based on several different genes. French researcher Heike Edinger explains that the biggest threat to UK rape growers is the breakdown of resistance to Phoma, especially varieties relying on single gene resistance.

"Multi gene resistance is superior as races of the pathogen change. If the UK weather becomes more like France, then Phoma will be the disease of significance throughout the UK. This proves the importance of multi gene resistance of Astrid and Alienor, which has helped make these two varieties popular in France as well as in the UK," she says.

Neil Groom points out that the high seasonal threat together with the fact that early infections of Phoma result in the worst consequences, will mean that growers should protect their vulnerable seedlings by sowing a highly resistant rape variety. "Their use may not obviate the need for fungicide treatments altogether, but offer more flexible timings and possible fewer applications- and a robust start which is all important for rape."

"The importance of this early inherent protection against Phoma was reflected in the results of this year's NIAB disease nursery trials, conducted by Dr. Jane Thomas. Es Astrid, which has a 7 disease rating against Phoma stem canker, had just 1.17% Phoma leaf spotting and a Canker Index of just 3.21 and this was reflected in its high yield of 3.8 t/ha. Also with a 7 Phoma rating, Alienor showed just 1.67% Phoma leaf spotting, a Canker Index of 5.46 and a mean yield of 4.2 t/ha," he reports.

Neil Groom warns that Phoma continues to be the most significant rape disease in England, affecting over 95% of the national crop and causing up to £50 million loss to growers. "If left untreated, it can reduce yields by up to 50% due to premature plant death. It can easily cause yield losses of between 0.5 and 1 t/ha, which at today's rape price would make significant inroads to crop profitability. Controlling this disease needs careful management including the use of rape varieties with ratings of 7 or above, cultivations, rotations and suitable fungicides."

He also points out that high disease ratings can be allocated a value. "Dr. Peter Gladders of ADAS has commented that that disease prevention by varietal resistance and/or fungicide usage is key to the production of high yielding crops. He estimates that every one point in disease resistance ratings is worth at least an additional £20/ha plus, of course, the benefit of disease prevention. With Astrid and Alienor having disease rating at least 2 points above most other key UK oilseed rape varieties, this will make an important contribution to the overall gross margin calculation."

For further comment and information, please contact Neil Groom, Technical, Grainseed Ltd on 01379 871073 or 07774 720240 or via email at neil@grainseed.co.uk