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Very close up shot of wheat crop ears in field

Summer disease assessment

Winter Oilseed Rape Disease Survey: Summer 2017

Defra has carried out annual stratified surveys of diseases of commercially-managed winter oilseed rape since 1987. Between 80 and 100 randomly selected crops are assessed for symptoms of disease at three growth stages during the cropping year, at mid leaf production (December), stem extension (March) and pod ripening (July) and information about the agronomic practices associated with each crop are collected. The following report summarises the results of the survey carried out at pod ripening in 2017.

Stems and pods of twenty-five plants selected at random from each surveyed crop were assessed visually at pod ripening for symptoms of disease.

This summer, 78% of crops were affected by phoma canker. This was a lower proportion to last year, when 85% crops were affected. Levels of infection within crops were also lower than last year with 21% stems affected compared with 27% stems in 2016. Canker incidence this summer was also lower than the long-term mean (2006-2015) of 86% crops and 28% stems affected. The proportion of crops affected by total phoma (phoma canker and phoma stem lesions) was also lower, with 84% crops affected compared with 91% crops affected last summer and 92% crops affected as the long-term mean. Within crops, the total phoma incidence was also lower, with 25% stems affected compared with 39% stems affected in the summer of 2016 and 33% stems affected in the long-term mean. The highest incidence of phoma canker occurred in the South West, where 88% crops were affected which was considerably higher than incidence in the North, where 56% crops were affected.

Light leaf spot incidence in 2017 was markedly lower than last year (when the highest incidence of light leaf spot was recorded since the survey began in 1987). On the pods, the disease affected 61% crops and 14% plants compared with 95% crops and 57% plants affected in 2016. Levels were also lower than the long-term mean (2006-2015) of 53% crops and 18% plants affected. On the stems, light leaf spot affected 83% crops and 36% stems and this was lower than both last year (100% crops and 81% stems affected) and the long-term mean (79% crops and 39% stems affected). Regionally, the highest incidence of light leaf spot on the stems was in the Midlands & West where 100% crops were affected and the lowest in the East (69% crops affected) and within crops, incidence ranged from 52% stems affected in the North to 14% stems affected in the South East. On the pods, the incidence ranged from 100% crops affected in the South West to 41% crops affected in the East. Within these crops, the highest incidence of light leaf spot on the pods was in the Midlands & West (21% of plants affected) and the lowest in the East (11% plants affected). The incidence of light leaf spot on both the pods and stems was the lowest seen since 2013.

Levels of powdery mildew on the pods were very similar to last year, with 14% crops and 2% plants affected compared with 15% crops and 2% plants in 2016, but lower than the long-term mean (2006-2015) of 23% crops and 7% plants affected. However, on the stems, 46% crops and 10% stems were affected which was much higher than last year when 15% crops and 3% stems were affected, and also higher than the long-term mean of 30% crops and 9% stems affected. This was the highest incidence of powdery mildew on the stems since 2007 when 74% crops and 38% stems were affected. The region with the highest incidence of powdery mildew on the stems was the South East, with 80% crops and 20% stems affected and the lowest was the Midlands & West, where 29% crops and 2% stems were affected. The South East was also the region with the highest incidence of powdery mildew on the pods (30% crops and 4% plants affected) and the South West had the lowest incidence, as the disease was not recorded on any surveyed pods in this region.

Sclerotinia stem rot affected 8% crops and 1% stems this summer, this was the same proportion of crops and stems affected as last year but lower than the long-term mean (2006-2015) of 14% crops and 2% stems affected. Regionally, the highest incidence of sclerotinia stem rot was the East where 14% crops and 2% plants were affected. Sclerotinia stem rot was not recorded on any surveyed crops in the Midlands & West and South East regions. Sclerotinia disease on the pods only affected crops in the East region (where 3.4% crops and 0.7% plants were affected), this gave a national average of 1% crops and 0.3% plants affected – lower than last year when 4% crops and 0.4% plants were affected, but higher than the long-term mean of 0.2% crops and 0.02% plants affected.

Alternaria pod spot was recorded on 49% crops and 8% plants, a higher incidence than last year when 32% crops and 4% plants were affected, but lower than the long-term mean (2006-2015) of 63% crops and 12% plants affected. On the stems, Alternaria affected 12% crops and 1% stems, which was higher than last year (5% crops and 0.2% stems) and similar to the long-term mean of 10% crops and 2% stems affected. Alternaria pod spot affected crops in all regions in the survey, with the South East having the highest incidence (70% crops and 21% plants affected) and the East with the lowest (41% crops and 4% stems affected). On the stems, the Midlands & West had the highest incidence of Alternaria, with 21% crops and 1% stems affected and the region with the lowest incidence was the North, where it was not recorded on any stems in the survey.

Botrytis on the pods was recorded at higher levels compared to last year, but lower than the long-term mean (2006-2015). This summer, 67% crops and 11% plants were affected compared with 57% crops and 11% plants affected in 2016 and 71% crops and 19% stems affected in the long-term. On the stems, Botrytis affected 5% crops and 0.3% stems, which was also slightly higher than last year (3% crops and 0.1% stems affected), but lower than the long-term mean of 14% crops and 2% stems affected. On the pods, Botrytis was recorded in all regions of the survey, with the East having the highest incidence (79% crops and 16% plants affected) and the South East with the lowest (50% crops and 9% plants affected). On the stems, Botrytis was only recorded in the East, Midlands & West and South East regions, with the highest incidence being in the South East, with 20% crops and 1% stems affected.

Verticillium wilt was reported for the seventh year in the survey and this summer saw the highest incidence of the disease seen since 2014. Twenty percent crops were found to be affected and within crops, 2% stems were affected by the disease. This was higher than in the previous year when 3% crops and 0.2% plants were affected. This summer, Verticillium wilt was found in all regions in the survey, except for the North. The region with the highest incidence was the South East where 40% crops and 5% stems were affected.

Downy mildew on the pods affected 8% crops and 0.4% plants this summer, this is the first time that it had been recorded on any surveyed pods since 2013 and it is the highest incidence since 2010, when 34% crops and 6% plants were affected. The region with the highest incidence was the Midlands & West with 21% crops and 1% plants affected and the lowest was in the East where none of the surveyed crops were affected. Downy mildew was not recorded on any stems this summer, the last time downy mildew was recorded on the stems in the survey was in 2009.

Incidence of diseases on the pods - % plants affected

Incidence of diseases on the stems - % plants affected. * Please note – no long-term verticillium data available *

Regional incidence of diseases on the pods - % plants affected

Regional incidence of diseases on the stems - % plants affected