Spring disease assessment

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

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

  • Light leaf spot affected 60% crops and 12% plants in spring, which was slightly lower than last year (64% crops and 15% plants affected) and the lowest incidence in the survey since 2007 when 39% crops and 11% plants were affected. Light leaf spot was also the most severe disease in the survey this spring affecting 0.3% total leaf area, however, this was less severe than last year when 0.5% total leaf area was affected. The disease affected crops in all regions, with the North showing the highest incidence (94% crops and 26% plants affected) and also the greatest severity (0.8% total leaf area affected)
  • Phoma leaf spot affected 94% crops and 46% plants, which was higher than last year when 90% crops and 32% plants were affected. This is the highest proportion of plants affected in the survey since 2004 (64% plants affected). The severity of the disease was also higher than last year, with a national mean of 0.4% total leaf area affected compared with 0.1% total leaf area in spring 2018. Phoma leaf spot affected crops in all regions with the South East having the highest incidence with 100% crops and 63% plants affected. The region with the lowest incidence was the South West, where 75% crops and 26% plants were affected.
  • Nationally, Alternaria leaf spot affected 11% crops and 0.6% plants this spring, which was much lower than last year when 30% crops and 2% plants were affected. It was the lowest incidence of Alternaria leaf spot in the survey since 2013, when 1% crops and 0.04% plants were affected. Alternaria leaf spot was recorded on crops in all regions in the survey this spring and the South West had the highest incidence with 50% crops and 3% plants 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 15% crops and 1% plants this spring. This was very similar to last year when 16% crops and 1% plants were affected. The disease was recorded in all regions in the survey this spring and the region with the highest incidence was the South East with 20% crops and 3% plants affected. Severity of the disease was low, with a mean of less than 0.05% total leaf area affected in all regions.
  • Powdery mildew was only recorded on surveyed crops in the Midlands & West (21% crops and 8% plants affected) and East (10% crops and 1% plants affected) regions this spring. This gave a national incidence of 8% crops and 2% plants affected which was higher than last year when powdery mildew was not recorded on any surveyed crops. The severity of powdery mildew was low, with both regions having less than 0.05% total leaf area affected.
  • White leaf spot, ring spot and botrytis were not found in any surveyed crop this spring.

Incidence of diseases on the leaf - % crops affected
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