Highlights from the 2004/2005 Oilseed rape survey
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Incidence of dark leaf and pod spot National incidence of dark leaf and pod spot in both the autumn and summer were very similar to levels recorded in 2003/2004. Incidence of 1.2% plants affected with dark leaf spot in the spring was lower than in 2004 when 2.7% plants were affected (Fig. 1). As in the previous year, the lowest incidence of dark leaf spot in the autumn was in the South West with 3.5% plants affected. In the spring and summer however, the South West had the highest incidence with 4.0% plants affected in the spring and 73.0% in the summer. |
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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 was lower than in the previous year at all assessment times (Fig. 2). In the autumn 7.3% plants were affected compared with 18.6% in 2003/04. In the spring 2.2% plants were affected compared to 12.5% in 2003/2004, and no plants were affected in the summer compared with 3.1% in 2003/04. Downy mildew was not found in the South West region at any assessment time. |
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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 Low incidence of light leaf spot (0.2% plants affected) was recorded in the autumn (Fig. 3). This was the first time the disease has been recorded in the autumn since 2001/2002. The incidence of light leaf spot in the spring was lower than in the previous year with 1.8% plants affected compared to 3.2%. This was the lowest spring incidence recorded in the survey to date. The incidence of light leaf spot in the summer, although higher than in the previous year (6.8% plants affected compared 3.1% plants affected), was otherwise lower than in any year since 1996. The Northern region saw the highest incidence of light leaf spot at all assessment times, which is consistent with trends noted in previous years. |
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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 Phoma leaf spot was the disease most commonly found in the autumn and spring. Autumn levels (52.1% plants affected) were much higher than in the previous season (24.2% plants were affected), but similar to levels recorded in 2003 (48.6% plants affected). In the spring, the incidence was lower than in the previous year with 45.4% plants affected compared to 63.7%. In the autumn and spring, phoma leaf spot was found in all regions, with the Northern region having the lowest incidence. In the summer phoma pod spot was only found in the Eastern regions, and nationally, mean incidence of 0.1% plants affected was lower in the previous year (0.6% plants affected). On the stems in summer, total phoma incidence (cankers and stem legions) of 38.7% plants affected was higher than in the previous year when 26.6% plants were affected. The South Western region had the highest incidence of total phoma on the stems in summer. |
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| Fig. 4 Percentage of plants affected by phoma leaf and pod spot |
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| Disease severity In the autumn, a mean of 0.4% total leaf area was affected by disease (Fig. 5). This was lower than the previous year when 0.7% total leaf area was affected. Phoma leaf spot was the most severe disease, accounting for almost all leaf the leaf area affected, with other diseases found at trace levels only. The region with the highest mean disease severity was the Midlands and West and the lowest was the South East. In the spring, a mean of 0.2% total leaf area was affected by disease, this is the lowest disease severity in spring since the survey began in 1987. Phoma leaf spot was again the most severe disease accounting for almost all leaf area affected. The region with the highest disease severity was the Midlands and West and the lowest the North. In the summer, mean disease severity on the pods was, at 1.7% pod area affected, higher than in the previous year when a mean of 1.0% pod area was affected. Botrytis was the most severe disease affecting 1.0% total pod area, this was followed by dark pod spot which affected a mean pod area of 0.5%. The highest mean severity was recorded in the South West region, and the lowest in the Midlands and West. |
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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 (Fig 6). Incidence was recorded at 93.7% crops and 27.4% stems affected, which was generally higher than in the previous year when 92.8% crops and 11.7% stems were affected. Light leaf spot was the second most common disease of the stems, affecting 23.2% crops and 9.6% stems. Although not recorded in any crop in either the South West or South Eastern regions, mean incidence of light leaf spot was lower than in the previuos year when 24.7% crops and 5.6% stems were affected. Incidence of Sclerotinia stem rot (17.9% crops and 1.9% stems affected) was higher than in the previous year with when 12.4% crops and 1.0% stems were affected. Sclerotinia stem rot was recorded in all regions, with the South West having the highest incidence of the disease. |
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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 Seventy-five per cent of crops received a fungicide treatment in the autumn (growth stage 1), an increase from the previous year when 51.6% crops were treated (Fig. 7). In the spring, 51.0% crops were treated, a decrease from the previous year (54.9% crops treated). At flowering, 39.8% crops received treatment, which was also a decrease from last years 47.3% crops treated. The proportion of crops receiving a post flowering treatment was 7.1%, much higher than in recent years. |
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| Fig. 7 Proportion of crops treated with fungicide in the four main periods |
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Insecticide applications The proportion of crops receiving an insecticide treatment was higher in both the autumn and spring compared to last year (Fig. 8). In the autumn, 71.4% crops were treated compared with 57.6% last year, and in the spring 31.6% crops were treated compared with 23.9% last year. As in all previous years, the majority of insecticide treatments were applied in the autumn (growth stage 1). The proportion of crops treated with insecticide in the summer decreased from 33.7% last year to 22.4% this year. Eight per cent of crops were treated post-flowering which was in contrast to the previous two years when no insecticides were applied at this time. |
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| Fig. 8 Proportion of crops treated with insecticide in the four main periods |
