Highlights from the 2003/2004 Oilseed rape survey
|
Incidence of dark leaf and pod spot Nationally, the percentage plants affected by dark leaf and pod spot was higher than in 2002/2003 (Fig. 1). The highest incidence in the autumn was recorded in the the South East, with 42.2% plants affected, whereas the lowest incidence was in the South West with 28.6% plants affected. In the spring and summer however, the South West region had the highest incidence with 81.1% spring and 52.6% summer plants affected. |
 |
| 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 The incidence of downy mildew was lower than in the previous season at all assessment times (Fig. 2). In the autumn, 18.6% plants were affected in 2004 compared to 30.7% in 2002/03. In the spring 12.5% plants were affected in 2004 compared to 24.7% in 2003, and in the summer 3.1% plants were affected in 2004 compared to 13.7% in 2003. The highest incidence was recorded in the East in the autumn, and in the North in both the spring and summer. |
 |
| 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 Throughout the 2003/2004 season, the incidence of light leaf spot was recorded at lower levels than in 2002/2003 (Fig. 3). Light leaf spot was not recorded at all in the autumn. Spring incidence of 3.2% plants affected was slightly lower then levels recorded in 1998 (3.5%) which was previously the lowest spring incidence since the survey began in 1987. Pod incidence of 3.1% plants affected was markedly lower than any recorded since the survey began in 1987. In the spring and summer, the highest incidence of the disease was recorded in the Northern region, and the lowest incidences were recorded in the Midlands and West and South West regions, which is similar to previous years' trends. |
 |
| Fig. 3 Percentage of plants affected by light leaf spot (autumn and spring samples refer to leaves and summer to pods) |
|
Incidence of phoma The incidence of phoma leaf spot and canker was lower than in 2002/2003, with the exception of the spring when levels of 63.7% plants affected were considerably higher than 43.2% plants affected in 2003. This spring incidence was the highest recorded since the survey began in 1987. 26.6% stems were affected in the summer, which was a marked decrease from 69.7% stems affected in 2003 (Fig. 4). The lowest incidence of canker occurred in the North, which was consistent with previous years' regional trends. |
 |
| Fig. 4 Percentage of plants affected by phoma leaf and pod spot |
|
Disease severity In 2004, a mean of 0.7% total leaf area was affected by disease in the autumn, which was slightly lower than 0.8% leaf area affected in the previous year (Fig. 5). As in previous years, phoma leaf spot and downy mildew were the most severe diseases in the autumn, with each affecting 0.3% of the leaf area. In the spring, a mean of 0.8% leaf area was affected by disease, which was slightly lower than the previous year when 1.3% leaf area was affected. Phoma leaf spot and light leaf spot were the most severe diseases, with 0.7% and 0.1% of the leaf area affected respectively. In the summer, total mean disease severity on the pods was, at 1.0% area affected, much lower than in the previous year, when a mean of 5.1% pod area was affected. Dark pod spot was the most severe disease affecting a mean of 0.5% pod area, this was followed by powdery mildew which affected a mean of 0.3% pod area. |
 |
| 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 years, phoma canker was the most common disease on the stems. In 2004 levels recorded were lower than in the previous year with 92.8% crops and 26.6% stems affected compared with 98.9% crops and 69.7% stems in 2003 (Fig 6). In 2004, light leaf spot was the second most common disease on the stems, and levels were also lower than in 2003 with 24.7% crops and 5.6% stems affected compared to 63.8% crops and 19.1% stems. Incidence of Sclerotinia stem rot was also lower than in the previous season with 12.4% crops and 1.0% stems affected, compared to 31.2% and 3.3% respectively last year. |
 |
| Fig. 6 Percentage of stems affected by canker, light leaf spot and sclerotinia stem rot at pod ripening |
|
Fungicide applications The proportion of crops receiving a fungicide treatment in the autumn (growth stage 1) was 51.6%, this was a decrease from the previous year when 67.4% of crops were treated (Fig. 7). In the spring, 54.9% of crops were treated, also a decrease from the previous year when 73.9% crops were treated. The proportion of crops receiving treatment at flowering increased from 28.3% crops last year to 47.3% crops this year. No crops received a fungicide treatment post-flowering. |
 |
| Fig. 7 Proportion of crops treated with fungicide in the four main periods |
| |
|
Insecticide applications As in all previous years, the majority of insecticide treatments were applied in the autumn/winter. The number of crops receiving a spray in the autumn/winter decreased slightly from 61.5% crops the previous year to 57.6% crops. The proportion of crops receiving an insecticide in the spring decreased slightly from 26.4% crops in 2003 to 23.9% crops in 2004. The proportion of crops receiving treatment at flowering increased from 16.5% crops to 33.7% crops, the highest proportion of crops treated at flowering since 1997. No crops received an insecticide treatment post-flowering in 2004. |
 |
| Fig. 8 Proportion of crops treated with insecticide in the four main periods |
