Highlights from the 2006/2007 Oilseed Rape Survey
Introduction
One hundred crops were monitored in the 2006/2007 season. The number of crops monitored
per region was proportional to the area of oilseed grown. Crops were assessed three times
throughout the season. Twenty-five plants from each crop were assessed in the autumn during
leaf production, in the spring during stem extension and in the summer at pod ripening.
Agronomic data and information on pesticide inputs were recorded for each crop.
Incidence of dark leaf and pod spot
National incidence of dark leaf and pod spot was recorded at similar low levels in the
autumn (1.0% plants affected) and spring (0.4% plants affected) to those in 2005/2006
(1.3% and 0.6% plants affected respectively) (Fig. 1). The disease was recorded at higher
levels on the pods in the summer than in the previous year, with 23.6% plants affected,
compared with 18.2%. The severity of the disease remained low throughout the whole survey year,
with only trace levels found at each assessment time.
Fig. 1 Percentage of plants affected by dark leaf and pod spot
(autumn and spring samples refer to leaves and summer to pods)
Incidence of downy mildew
Throughout the season, incidence of downy mildew remained low with 3.7% plants affected
in the autumn, 2.3% plants affected in the spring and no downy mildew recorded in the summer.
This continues the trend towards decreasing incidence of the disease. Autumn and spring
incidence of the disease has been falling since 1997, however, summer incidence has remained
more variable. The severity of the disease in the autumn and spring was low, with only trace
levels found. Downy mildew was not recorded on the stems during the summer assessment and has
not been found on any stems in the survey since 1991.
Fig. 2 Percentage of plants affected by downy mildew
(autumn and spring samples refer to leaves and summer to pods)
Incidence of light leaf spot
During the autumn, light leaf spot was found at similar levels to last year with 1.2% plants
affected compared with 1.3% plants affected in 2005/2006 (Fig. 3). The incidence of the
disease was markedly different from last year during both the spring and summer assessments
- higher in the spring with 11.8% plants affected compared with 4.9% last year, and lower in the
summer with 1.0% plants affected compared with 8.5%. Incidence in the spring was the highest
since 2002 (when 18.1% plants were affected). During the summer assessments, incidence was much
lower than in previous years, with 1.0% plants affected. This is the lowest national incidence
of the disease recorded on the pods in the summer since the survey began. Following trends noted
in previous years, the regions with the highest incidences of the disease were the North and
the South West.
Fig. 3 Percentage of plants affected by light leaf spot
(autumn and spring samples refer to leaves and summer to pods)
Incidence of phoma
Incidence of Phoma on the leaves was slightly lower than in the previous
year (2005/2006) with 36.0% plants affected in the autumn and 36.3% plants in the
spring, compared with 37.7% and 42.1% plants respectively last year (Fig. 4). Phoma
canker was also lower with 37.6% stems affected compared with 53.2% last year. However,
on the pods, Phoma was found on 5.3% plants this year compared with 1.2% last year.
This was the highest incidence on the pods since the survey began. Phoma was recorded
on the leaves, stems and pods in all regions with the highest incidence on the leaves
and stems in the Eastern region, and the highest incidence on the pods in the South East.
The severity of Phoma leaf and pod spot was low throughout the survey year with a mean of
0.1% leaf area affected in both the autumn and spring and only trace levels found on the pods.
Fig. 4 Percentage of plants affected by phoma
leaf spot in autumn and spring, and stems and pods in summer)
Disease Severity
In the autumn, a mean of 0.18% total leaf area was affected by disease (Fig. 5).
This was slightly lower than last year (2005/2006) when 0.23% total leaf area was
affected and was the lowest severity of autumn disease since the survey began. Phoma
leaf spot was the most severe disease, affecting 0.12% of the total leaf area. The
region with highest mean disease severity was the East, and the lowest the South East.
In the spring, a mean of 0.34% total leaf area was affected by disease. This was lower
than in the previous year when 0.5% total leaf area was affected. Light leaf spot was
the most severe disease, accounting for 0.28% of the total leaf area affected. The region
with the highest mean disease severity was the North, and the lowest the Midlands & West,
which was also the case in the spring of last year.
In the summer, a mean of 2.4% pod area was affected by disease. This was markedly higher
than the previous three years when 1.0% (2004), 1.7% (2005) and 0.7% (2006) total pod areas
were affected. This was largely due to powdery mildew which was the most severe disease,
affecting 1.98% total pod area. The region with the highest mean disease severity on the
pods was the South East with 4.25% total pod area affected and the lowest the North with
0.79% pod area affected.
Fig. 5 Percentage area affected by the sum of all diseases
(autumn and spring samples refer to leaves and summer to pods)
Stem Disease Incidence
On the stems this year, Phoma canker and powdery mildew were the two most common diseases
(Fig. 6). Phoma canker affected 92.0% crops and 37.6% stems, while powdery mildew affected
74.0% crops and 37.9% stems. Light leaf spot affected 56.0% crops and 17.6% stems in the
survey, higher than last year, when 45.5% crops and 14.7% stems were affected. Incidence of
Sclerotinia stem rot was also higher than in the previous year (2005/2006) with 34.0% crops
and 5.7% stems affected compared with 20.2% crops and 2.3% stems last year. The incidence of
Phoma canker was lower than last year when 94.9% crops and 45.7% stems were affected. This
year saw the highest incidence of crops affected by powdery mildew on the stems since the
survey began. The incidence of Sclerotinia stem rot was also at its highest level recorded
in the survey since 1991 (when 44.3% crops and 5.4% stems were affected). Phoma canker,
powdery mildew, light leaf spot and Sclerotinia stem rot were recorded on the stems in all regions.
Fig. 6 Percentage of stems affected by canker, light leaf spot
and sclerotinia stem rot at pod ripening
