Highlights from the 2002/2003 Oilseed rape survey
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Incidence of dark leaf and pod spot Nationally, the percentage plants affected by dark leaf and pod spot was lower than in 2001/2002 (Fig. 1). The highest incidence in both the autumn and the spring was recorded in the the North, with 7.5% and 3.3% plants affected respectviely. In the summer however, the Northern region had the lowest incidence with only 6.8% plants affected, the highest incidence recorded was in the South-West, where 81.1% plants were affected. |
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| Fig. 1 Percentage of plants affected by dark leaf and pod spot (autumn and spring samples refer to leaves and summer to pods) |
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Incidence of downy mildew The incidence of downy mildew increased from the previous year in both the autumn and summer, although, in the spring incidence decreased (Fig. 2). In the autumn, incidence increased from 15.7% plants affected in 2001/2002 to 30.7% plants affected in 2003 and in the summer it increased from 2.9% plants affected to 13.7% plants affected. The highest incidence was recorded in the East in the autumn and spring, and in the south-West in the summer at pod development. |
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| Fig. 2 Percentage of plants affected by downy mildew (autumn and spring samples refer to leaves and summer to pods) |
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Incidence of light leaf spot Throughout the 2002/2003 season, the incidence of light leaf spot was recorded at lower levels than in 2001/2002 (Fig. 3). Nationally, there were less than 0.05% (autumn), 11.4% (spring) and 10.7% (summer) plants affected, compared with 0.2% (autumn), 18.1% (spring) and 16.0% (summer) in 2002. In the autumn, the disease was recorded in the Midlands and Western region only. In both the spring and the summer, the highest incidence was recorded in the South-West. |
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| Fig. 3 Percentage of plants affected by light leaf spot autumn and spring samples refer to leaves and summer to pods) |
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Incidence of phoma The incidence of phoma leaf spot and canker was higher than in the 2001/2002, but it was the summer which saw the biggest increase from last year, with levels rising from 53% to 70% plants affected (Fig. 4). This is the highest level recorded since the survey began. Highest incidences of canker occurred in the north and east. |
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| Fig. 4 Percentage of plants affected by phoma leaf and pod spot |
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Disease severity In 2003, the total leaf area affected by disease in the autumn was 0.7%, which was slightly higher than the 0.5% 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 accounting for 0.5% and 0.2% leaf area affected respectively. In the spring, 1.3% leaf area was affected by disease, which was slightly lower than the previous year when 1.4% leaf area was affected. Phoma leaf spot and light leaf spot were the most severe diseases, each affecting 0.4% of the leaf area, downy mildew was the next most severe, affecting 0.3% leaf area. Generally, the severity of phoma remained similar to levels recorded in 2002, with the exception of spring, when 0.4% leaf area was affected in 2003 compared to a mean of 0.1% area affected nationally in 2002. In the summer, total disease severity on the pods was, at 5.1% area affected, the highest recorded since 1987, when levels of 5.7% were reached. Powdery mildew was the most severe disease affecting 3.9% pod area, this was followed by dark pod spot and light leaf spot, affecting 0.6% and 0.4% respectively. |
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| Fig. 5 Percentage area affected by the sum of all diseases (autumn and spring samples refer to leaves and summer to pods) |
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Stem disease incidence As in previous years, phoma canker was the most common disease on the stems, this year the levels recorded were the highest since the survey began, with 98.9% crops and 69.7% stems being affected (Fig 6). Light leaf spot affected 63.8% crops and 19.1% stems, which was lower than last year, when 81.4% crops and 30.2% stems were affected. Sclerotinia stem rot was slightly higher with 30.9% crops and 3.2% stems affected, compared to 19.6% and 2.3% respectively last year. Powdery mildew was the second most common disease, affecting 38.1% stems. |
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| Fig. 6 Percentage of stems affected by canker, light leaf spot and sclerotinia stem rot at pod ripening |
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Fungicide applications The proportion of crops receiving a fungicide treatment in the autumn (growth stage 1) was 66.7%, this was a decrease on last year when 83.0% of crops were treated (Fig. 7). In the spring, 74.4% of crops were treated, an increase from last year's 67.7%. The proportion of crops receiving treatment at flowering and post-flowering remained similar to 2002, with 28.9% treated at flowering and 1.1% post-flowering. |
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| Fig. 7 Proportion of crops treated with fungicide in the four main periods |
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Insecticide applications As in all previous years, the majority of insecticide treatments were applied in the autumn/winter, although in 2003 this figure (61.8% crops) was lower than in 2002, when 75.3% crops were treated (Fig. 8) . The proportion of crops receiving an insecticide in the spring rose from 10.8% in 2002 to 27.0% in 2003. The proportion of crops receiving treatment at flowering rose from 11.8% in 2002 to 16.9% in 2003. No crops received an insecticide treatment at the post-flowering stage in 2003. |
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| Fig. 8 Proportion of crops treated with insecticide in the four main periods |
