Farmers in mainstream oilseed rape growing regions looking to cut autumn workloads will benefit from selecting varieties with better disease resistance ratings.

That is the view of KWS product development manager, John Miles, based on trials comparing phoma control programmes at ADAS Terrington, Norfolk, last year.

Mr Miles said: “They show that the right variety selection will give you flexibility in terms of autumn spraying needs.

“In the ADAS work, even after two sprays, the susceptible control variety – rated four for the disease – still had phoma index scores of between ten and 20.

“In comparison cash, rated seven for the disease had an index score of five or lower, significantly cutting the risks of the disease leading to stem canker and significant yield loss in the summer.”

Mr Miles points out that strong variety resistance such as that provided by Cash does not negate the need for a sensible spray programme.

“With many crops, particularly in the eastern counties, needing at least two if not three sprays to keep the disease at bay through the autumn and winter, it simply buys time to get round the whole crop.

“As a result, growers should be looking to put a proportion of their crop down to varieties that have the best resistance ratings possible.”

The work which compared the use of Proline applied in mid-October, late November and then again mid-late February showed that treatments which included the first of these spray timings gave the best results.

There were also positive yield increases from a two or three-spray programme building on this mid-October treatment, with larger responses on the four-rated variety for phoma.

However, where sprays are delayed for whatever reason, the less resistant variety had yields that were between 0.5-0.6t/ha lower than that of the seven-rated variety for phoma resistance.

“This suggests that in a year when early spraying conditions are more difficult, a variety with a better disease resistance rating will be invaluable.

“It has to be stressed that these results were from 2010-2011, which was not a bad season for phoma, so as a result, responses are likely to be even higher in a year when the disease is more prevalent.

“My advice to those growing rape south of the Humber would be to ensure that at least a third or half of the area is in more resistant types, particularly if farmers are looking to increase their oilseed rape area.”

Mr Miles points out that this year growers have the new conventional rape variety Quartz, which has a perfect nine-rating for phoma in National List trials, available for the first time.

“With an exceptional gross output of 108 per cent Quartz is a strong candidate for the 2013 East/West Recommended List. By selecting Quartz there is no need to compromise on disease control for fear of missing out on output,” stressed Mr Miles.