Spring disease assessment

Brown rust risk map
Spring disease assessment
Winter Oilseed Rape Disease Survey: Spring assessment 2020

Twenty five plants from each surveyed crop were assessed visually for symptoms of disease at early stem extension.

  •  Light leaf spot affected 73% crops and 30% plants in spring, which was much higher than last year (60% crops and 12% plants affected) and was the highest incidence in the survey since 2015 when 85% crops and 34% plants were affected. Light leaf spot was also the most severe disease in the survey this spring affecting 1.2% total leaf area, this was more severe than last year when 0.3% total leaf area was affected. The disease affected crops in all regions, with the Midlands & West showing the highest incidence (88% crops and 45% plants affected) and the East had the lowest with 61% crops and 16% plants affected. The region with the highest severity of light leaf spot was the South West, with 1.9% total leaf area affected. The East had the lowest severity, with 0.5% total leaf area affected.

  • Phoma leaf spot affected 96% crops and 38% plants, compared with 94% crops and 46% plants affected last year. This is the highest proportion of crops affected in the survey since 2006 (98% crops affected). The severity of the disease was lower than last year, with a national mean of 0.2% total leaf area affected compared with 0.4% total leaf area in spring 2019. Phoma leaf spot affected crops in all regions with the East having the highest incidence with 100% crops and 45% plants affected. The South West had the lowest incidence of crops affected (88%) and within crops, the South East had the lowest incidence of plants affected (28%).

  • Nationally, Alternaria leaf spot affected 17% crops and 1% plants this spring, which was higher than last year when 11% crops and 0.6% plants were affected. Alternaria leaf spot was recorded on crops in all regions in the survey this spring and the South East had the highest incidence with 33% crops and 3% plants affected. The lowest incidence was in the South West where 13% crops and 0.5% plants were affected. Severity of the disease was low, with all regions having a mean of less than 0.05% total leaf area affected.

  • Downy mildew affected 3% crops and 0.1% plants this spring. This was much lower than last year when 15% crops and 1% plants were affected and was the lowest incidence of downy mildew in the spring since 2013 when there were 2% crops and 0.1% plants affected. The disease was only recorded in the North region in the survey this spring, where 11.8% crops and 0.5% plants were affected. Severity of the disease was low, with less than 0.05% total leaf area affected.

  • Powdery mildew affected 11% crops and 3% plants this spring which was higher than in spring 2018 when there were 8% crops and 2% plants affected. Powdery mildew was recorded in all regions of the survey, apart from the North. The region with the highest incidence of powdery mildew was the South East, where 44% crops and 19% plants were affected. The severity of powdery mildew was also highest in the South East, where 0.3% total leaf area was affected. Nationally, there was less than 0.05% total leaf area affected

  • White leaf spot, ring spot and botrytis were not found in any surveyed crop this spring.

Figure 1. Incidence of diseases on the leaf - % crops affected

Figure 2. Incidence of diseases on the leaf - % plants affected

Regional incidence of diseases on the leaf - % crops affected

Regional incidence of diseases on the leaf - % plants affected