Highlights from the 2005/2006 Oilseed Rape Survey
Introduction
One hundred crops were monitored in the 2005/2006 season. The numbers of crops sampled in each region was proportional to the area of oilseed grown.
Twenty-five plants were randomly selected from a crop at each assessment (in the autumn during leaf production,
in the spring during stem extension and in the summer at pod ripening) and visually assessed for disease symptoms.
Agronomic information and pesticide inputs were recorded for each crop.
Incidence of dark leaf and pod spot
Nationally, the incidence of dark leaf and pod spot was lower than in 2004/2005. This was consistent throughout the
whole survey year (Fig. 1). The mean incidence was 1.3% of plants affected in the autumn, 0.6% in the spring, and 18.2% in the summer.
This compared with 5.6%, 1.2% and 35.7% of plants respectively in the previous survey of 2004/2005. The regions with the highest incidence of the disease
on the pods were the South East, South West and Midlands & West. This is consistent with the long-term regional trend,
click to view map.
The severity (% leaf/pod area affected) of the disease remained low throughout the whole season 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
When compared with the previous survey year the incidence of downy mildew in the autumn was lower, 3.5% plants affected compared with 7.3%, continuing a
decline in autumn disease levels recorded since 2003/2004.
Disease incidence was recorded at higher levels in both the spring and summer 3.6% and 0.9% respectively compared with 2.2% and no plants affected
in the previous survey. However, although downy mildew incidence was higher than the last survey, both spring and summer levels were still lower than for any previous year since 1990 (Fig. 2).
Downy mildew was not recorded on any stems during the summer assessment and has not been recorded 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
Nationally the incidence of light leaf spot was higher than in the previous survey at all assessment times (Fig. 3). In the autumn 1.3% of
plants were affected compared with 0.2% in 2004/2005, in the spring 4.9% of plants were affected compared to 1.8%,
and in the summer 8.5% of plants were affected compared to 6.8%. As in the previous survey, the severity of the disease was generally low.
The regions where the highest incidence of light leaf spot was recorded in the summer, on both pods and stems, were the North and the South West, which is consistent with
trends noted in previous years.
Click to view map.
Fig. 3 Percentage of plants affected by
light leaf spot
(autumn and spring samples refer to leaves and summer to pods)
Incidence of phoma
Nationally, the proportion of crops affected by phoma symptoms was very similar to the previous survey in 2004/2005 with 97%, 98% and 94.9% of crops affected in the autumn, spring and summer respectively
compared with 97.9%, 94.9% and 93.7% in the previous survey. Phoma leaf spot was recorded in all regions in the autumn and spring, with the lowest incidence recorded in the Northern region at both of these assessment
times. Phoma canker on the stems affected 94.9% crops and 45.7% plants, this was
higher than in the previous survey when 93.7% crops and 27.4% plants were affected. Total phoma (stem canker and stem lesions) affected 53.2% of stems in 2006
(Fig. 4). The North and South West regions had the lowest proportion of plants affected
whilst the Eastern region had the highest proportion. This is generally consistent with long-termn trends,
click to view map.
The severity of phoma leaf spot was low throughout the season with a mean of 0.1% leaf area affected in both the autumn and spring.
Fig. 4 Percentage of plants affected by phoma
(leaf spot in autumn and spring, and stems in summer)
Disease Severity
In the autumn, a mean of 0.2% total leaf area was affected by disease (Fig. 5). This was lower than in 2004/2005 when 0.4%
total leaf area was affected and was also the lowest severity of autumn diseases since the survey began in 1987. Phoma leaf
spot was the most severe disease, accounting for just over half of the total leaf area affected. The region with the highest
mean disease severity was the North whilst the lowest was the South West.
In the spring, a mean of 0.5% total leaf area was affected by disease, which although higher than the previous survey (0.2% leaf
area affected), was the second lowest level recorded since the survey began.
Light leaf spot was the most severe disease, affecting 0.4% of the total leaf area. The region with the
highest total disease severity was the North and the lowest was the Midlands & West.
In the summer, mean disease severity on the pods was 0.7% pod area affected, which was markedly lower than in the previous survey
(1.7% pod area affected). Only in 1989, 1996 and 2001 was total pod disease lower.
Powdery mildew was the most severe disease (affecting 0.5% total pod area), followed by
light leaf spot, which affected 0.1% pod area. The region with the highest mean disease severity on the pods was the East and
the lowest was the Midlands & West.
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
As in previous surveys, phoma canker was the most common disease on the stems (Fig 6). Canker was recorded in 94.9% of
crops and 45.7% of stems affected, which was slightly higher than in the previous survey when 93.7% of crops and 27.4% of stems were affected.
Light leaf spot was the second most common disease on the stems, affecting 45.5% of crops and 14.7% of stems. Incidence of light leaf spot on the
stems was higher than in the previous survey affecting 23.2% of crops and 9.6% of stems. Incidence of Sclerotinia stem rot
was also higher than in the previous survey with 20.2% of crops and 2.3% of stems affected compared with 17.9% and 1.9% respectively in
2004/2005. Phoma, light leaf spot and Sclerotinia stem rot were recorded on stems in all regions.
Fig. 6 Percentage of stems affected by canker, light leaf spot and sclerotinia stem rot at pod ripening
Fungicide Applications
In the autumn/winter, 82.4% crops received a fungicide treatment. This was higher than in 2004/2005
when 75.5% crops were treated (Fig. 7). This trends follows the annual increase in light leaf spot incidence since 2003/2004.
In the spring (GS 1-3), 61.5% crops received a fungicide treatment, an increase from the
previous year when 51.0% crops were treated. There was also an increase in the number of crops receiving a fungicide treatment at
flowering (53.8% this year compared with 39.8% last year). The proportion of crops that received a post flowering spray was
3.3%, which was lower than last years 7.1% crops. A mean of 2.3 fungicide applications were made to surveyed crops.
Fig. 7 Proportion of crops treated with fungicide in the four main periods
Insecticide Applications
In the autumn, 73.6% crops received an insecticide treatment. This was similar to 2004/2005 when 71.4% crops received an insecticide spray (Fig. 8).
The proportion of crops receiving an insecticide treatment in the spring was 34.1% crops, also similar to last year (31.6%). However, there was a large increase
in crops being sprayed with insecticide during flowering, with 41.8% crops receiving a treatment compared with 22.4% in the previous year. This is the
highest proportion of crops to be sprayed with insecticide during flowering since the survey began in 1987. This was followed by a reduction (compared
to last year) in the number of insecticide sprays applied to crops post flowering, with 2.1% receiving treatment, compared to 8.2% in 2004/2005.
Fig. 8 Proportion of crops treated with insecticide in the four main periods
