Autumn disease assessment

Brown rust risk map
Autumn disease assessment
Winter Oilseed Rape Disease Survey: Autumn assessment 2018/2019

Twenty-five plants from each surveyed crop were assessed visually for symptoms of disease at mid leaf production (December).

  • Eighty-nine per cent of crops were affected with Phoma leaf spot in the autumn of 2018, which was slightly lower than the previous autumn when 91% crops were affected. Within crops, 40% plants were affected with phoma leaf spot which was the same proportion as the previous year. Phoma leaf spot was recorded in all regions in the survey, with the highest incidence in the South East and Midlands & West (where 100% crops were affected in both regions). The region with the lowest incidence was the North, where 69% crops were affected. National severity was low, with 0.1% mean total leaf area affected. This was the same severity as in the previous autumn.
  • Light leaf spot in autumn 2018 was recorded only on plants in the North and East regions of the survey, where there were 6% and 3% crops affected respectively. Within crops, there were 1% plants affected in the North and 0.1% plants affected in the East. This gave a national mean of 3% crops and 0.2% plants affected, which was lower than in the previous autumn when 4% crops and 1% plants were affected. This is the lowest incidence of light leaf spot in the survey during autumn since 2007/08 (when it was not recorded on any surveyed sample). The severity of light leaf spot was low, with less than 0.05% mean leaf area affected in both regions.
  • Alternaria leaf spot affected 49% crops and 4% plants in the autumn of 2018, this was lower than in the previous autumn when 65% crops and 10% plants were affected. Alternaria leaf spot was recorded in all regions in the survey. Regionally, the incidence of Alternaria leaf spot was highest in the South with 75% crops affected in the South West and 70% crops in the South East. The severity of Alternaria was low, with all regions having a mean of less than 0.05% total leaf area affected.
  • Downy mildew affected 18% crops and 4% plants this autumn which was lower than the previous year, when 28% crops and 5% plants were affected, and is the lowest incidence of downy mildew in the autumn since 2011/12 (13% crops and 2% plants affected). Downy mildew was recorded in crops from all regions in the survey, except the South West. Regionally, the highest incidence was in the South East where 30% crops and 11% plants were affected. The severity of downy mildew was low throughout the country, with a national mean of less than 0.05% total leaf area affected.
  • Nationally, powdery mildew affected 11% crops and 4% plants this autumn which was slightly lower than last year (when 19% crops and 5% plants were affected). Powdery mildew was recorded in all regions in the survey apart from the Midlands & West. Regionally, the incidence of powdery mildew was highest in South West, where 25% crops and 6% plants were affected. The severity of the disease was low across all regions, giving a national mean of 0.1% mean leaf area affected.
  • Ring spot, Botrytis and white leaf spot were not recorded on any surveyed crop this autumn.

Figure 1. Incidence of diseases on the leaf - % crops affected
Figure 2. Incidence of diseases on the leaf - % plants affected
Figure 3. Regional incidence of diseases on the leaf - % crops affected
Figure 4. Regional incidence of diseases on the leaf - % plants affected