Summer disease assessment

Brown rust risk map
Summer disease assessment
Winter Oilseed Rape Disease Survey: Summer 2019

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 (June) 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 2019.

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, 82% of crops were affected by phoma canker. This was a lower proportion than last year, when 89% crops were affected. Levels of infection within crops were also lower than last year with 21% stems affected compared with 29% stems in 2018. Canker incidence this summer was also lower than the long-term mean (2008-2017) of 84% crops and 24% stems affected. The proportion of crops affected by total phoma (phoma canker and phoma stem lesions) was also lower this year, with 87% crops and 28% stems affected compared with 93% crops and 33% stems affected last summer and 90% crops and 29% stems affected in the long-term. The highest incidence of phoma canker occurred in the East, where 90% crops and 32% stems were affected and the region with the lowest was the North, with 69% crops and 8% stems affected.

  • Light leaf spot incidence in 2019 was lower on the stems but higher on the pods than last year. On the pods, the disease affected 73% crops and 19% plants compared with 62% crops and 17% plants affected in 2018. The incidence this year was lower than the long-term mean (2008-2017) of 64% crops and 23% plants affected. On the stems, light leaf spot affected 85% crops and 26% stems which was lower than last year (93% crops and 44% stems affected) and was the lowest incidence of stems affected since 2007 (18% stems affected). The incidence of light leaf spot on the stems this year was also lower than the long-term mean of 87% crops and 47% stems affected. Regionally, the highest incidence of light leaf spot on the stems was in the South West where 100% crops and 44% stems were affected and the lowest in the East (71% crops and 13% stems affected). On the pods, the incidence ranged from 100% crops affected in the Midlands & West to 58% crops affected in the East. Within these crops, the highest incidence of light leaf spot on the pods was in the Midlands & West (40% of plants affected) and the lowest in the North (7% plants affected).

  • Levels of powdery mildew on the pods were higher than last year, with 9% crops and 4% plants affected compared with 6% crops and 2% plants in 2018, but slightly lower than the long-term mean (2008-2017) of 16% crops and 3% plants affected. On the stems, 34% crops and 10% stems were affected compared with 36% crops and 7% stems affected in 2018. The incidence on the stems this summer was higher than the long-term mean of 25% crops and 6% stems affected. The region with the highest incidence of powdery mildew on the stems was the South East, with 100% crops and 21% stems affected. The region with the lowest proportion of crops affected was the East (19% crops) and within crops, the region with the lowest proportion of stems affected was the South West (4% stems). On the pods, the South East had the highest proportion of crops affected (30%) and the East had the highest proportion of plants affected (6%). The South West had the lowest incidence, where the disease was not recorded on any surveyed pods in this region.

  • Sclerotinia stem rot affected 10% crops and 1% stems this summer, which was higher than last year when 5% crops and 0.4% stems were affected but slightly lower than the long-term mean (2008-2017) of 10% crops and 2% stems affected. Regionally, the highest incidence of sclerotinia stem rot was the North (25% crops and 3% stems affected) and the lowest the South East where the disease was not recorded on any surveyed crop. Sclerotinia disease on the pods affected 4% crops and 0.2% plants. This was higher than last year when the disease was not recorded on any surveyed pods and also higher than the long-term mean of 1% crops affected.

  • Alternaria pod spot was recorded on 60% crops and 15% plants, a markedly higher incidence than last year (32% crops and 4% plants affected) and the highest incidence on the pods since 2014 when 69% crops and 14% plants were affected. The incidence on the pods this summer was also higher than the long-term mean (2008-2017) of 56% crops and 10% plants affected. On the stems, Alternaria affected 5% crops and 1% stems, which was also higher than last year when 3% crops and 0.1% stems were affected but lower than the long-term mean of 6% crops and 1% stems affected. On the pods, the region with the highest incidence was the South East (100% crops and 69% plants affected) and the lowest was the North (38% crops and 4% plants affected). On the stems, Alternaria was only recorded on samples from the Midlands & West (7% crops and 0.3% stems affected) and the South East (30% crops and 4% stems affected) regions.

  • Botrytis on the pods was recorded at higher levels compared to last year and similar levels compared with the long-term mean (2008-2017). This summer, 77% crops and 18% plants were affected compared with 72% crops and 11% plants affected in 2018 and 74% crops and 19% stems affected in the long-term. This is the highest incidence of Botrytis on the pods since 2012, when 91% crops and 38% plants were affected. On the stems, Botrytis affected 9% crops and 1% stems which was higher than last year when it was not recorded on any surveyed crops. It was, however, lower than the long-term mean of 12% crops and 2% stems affected. On the pods, Botrytis was recorded in all regions of the survey, with the South West having the highest incidence (88% crops affected) and the North with the lowest (56% crops affected). On the stems, the region with the highest incidence was the South East with 20% crops affected and the lowest in the South West where it was not recorded on any stems.

  • Verticillium wilt has been recorded in the survey since the summer of 2011. This summer, 14% crops and 1% plants were affected. This was higher than in the previous year when 5% crops and 0.4% plants were affected. Verticillium wilt was found in all regions in the survey, except for the North and South West. The region with the highest incidence was the South East where 30% crops and 2% stems were affected.

  • This summer, downy mildew was not recorded on either the pods or stems of any surveyed crop. Downy mildew was present on the pods last summer (1% crops and 0.1% plants affected) but 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