Autumn disease assessment

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

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

• One hundred per cent of crops were affected with Phoma leaf spot in the autumn of 2019, this was higher than in the previous autumn (89% crops affected) and is the highest incidence of Phoma leaf spot in the autumn since the survey began in 1987. Within crops, 65% plants were affected with phoma leaf spot which is the highest proportion of plants affected since the survey began and much higher than the 40% affected last autumn. Phoma leaf spot was recorded in all regions in the survey. All regions had 100% crops affected but within crops, the region with the highest proportion of plants affected was the East, with 74% and the region with the lowest proportion of plants affected was the North (56%). National severity was low, with 0.7% mean total leaf area affected, however, this was higher than in the previous year when 0.1% mean total leaf area was affected.

• The incidence of light leaf spot in the autumn was higher than in the previous year, with 13% crops and 2.0% plants affected compared with 3% crops and 0.2% plants affected in autumn 2018. This is the highest incidence of light leaf spot in the survey since 2014, when 17% crops and 2% plants were affected in the autumn. Light leaf spot was recorded in plants in all regions of the survey. The region with the highest incidence of crops affected was the South East (20% crops affected) and the lowest was the East (10% crops affected). Within crops, the South West had the highest proportion of plants affected (8%) and the lowest was the Midlands & West (0.5% plants affected). The severity of light leaf spot was low, with less than 0.05% mean leaf area affected in all regions except the South West, where 0.1% mean leaf area was affected.

• Alternaria leaf spot affected 71% crops and 14% plants in the autumn of 2019, this was much higher than in the previous autumn when 49% crops and 4% plants were affected and is the highest incidence of Alternaria leaf spot since the survey began. Alternaria leaf spot was recorded in all regions in the survey. Geographically, the highest incidence of Alternaria leaf spot was in the South, with the South East having the highest proportion of crops affected (100%) and within crops, the South West with the highest proportion of plants affected (20%). The region with the lowest incidence was the North, with 53% crops and 7% plants affected. The severity of Alternaria was low, with all regions having a mean of less than 0.05% total leaf area affected.

• Downy mildew affected 9% crops and 1% plants this autumn which was lower than the previous year, when 18% crops and 4% plants were affected, and is the lowest incidence of downy mildew in the autumn since 2008 (7% crops and 1% plants affected). Downy mildew was only recorded in crops from the East and North regions in the survey this autumn. Of these two regions, the East had the highest incidence with 16% crops and 2% plants affected compared with 12% crops and 1% plants affected in the North. The severity of downy mildew was low in both regions, with both having a mean of less than 0.05% total leaf area affected.

• This autumn, powdery mildew was only recorded in the Northern region in the survey, with 6% crops and 0.2% plants affected. This gave a national incidence of 1% crops and 0.1% plants affected which was much lower than last year (when 11% crops and 4% plants affected) and is the lowest incidence of powdery mildew in the autumn since 2013 (1% crops and 0.04% plants affected). The severity of the disease was low, with both the incidence nationally and in the North being less than 0.05% 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