| Monitoring of Diseases in Winter Barley at GS 30 (2004) |
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Monitoring of the incidence and severity of diseases of winter barley has been carried out in a structured
survey of crops across England. The CropMonitor project, funded by Defra, which encompasses the national
survey of winter barley diseases carried out at grain filling, has extended the monitoring to include
an assessment at GS 30.
Approximately 100 crops of winter barley located across England were examined to assess the severity of foliar and stem base diseases at GS30. Crops were selected to reflect the area of winter barley grown and the profile of holding sizes in each region. Assessments were carried out on each leaf layer with the topmost leaf designated as leaf 1. The most popular cultivar was Pearl representing 61% of fields surveyed. Carat accounted for 12% of samples and was the only other variety to exceed 5% of the sample (Figure 1). |
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| Fig. 1 Cultivars surveyed in spring 2004 |
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Most winter barley had foliar diseases established on leaf 3 at GS 30, the key stage for making decisions
on fungicide treatments on winter barley. Fungicide product selection will be influenced by the range of
diseases present. |
| Results of disease assessments show that mildew was the most severe disease in winter barley nationally, affecting an average of 2.4% of leaf 3, whilst net blotch and rhynchosporium each affected less than 1% of the area of leaf 3 (Figure 2). Mildew was also the dominant disease on leaves 1 and 2, affecting 0.1% and 1.6% of the leaf area respectively. |
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| Fig. 2 National foliar disease levels at GS 30 |
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Rhynchosporium has been the most important disease of barley in recent years and it was evident in all regions.
The highest levels of Rhynchosporium were found in the South west and North East and North West regions (Figures 3 & 4).
The disease can develop rapidly in wet conditions and early control (before stem extension) is vital.
Robust mixtures of fungicides are required at GS30-31 to control Rhynchosporium where it is present in the crop.
Strobilurins are a key component in spray mixtures for Rhynchosporium control but will need mixture partners of
triazoles and morpholines where the disease is established. |
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Powdery mildew has caused few problems in recent years, but is showing rather greater activity this spring than in
recent years. There are indications of regional differences, with more mildew in the East and West Midlands and
further north. Some mildew is present on the top two leaves and specific fungicides for mildew control are justified
where this is detected. This increase in mildew levels may, in part, be related to the development of strobilurin
resistance in barley mildew populations which has developed in the last 2-3 years. Thus, mildew control is now
dependant on specific mildew products such as the morpholines, quinoxyfen and metrafenone. |
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Net blotch has been less active in recent years due to drier springs and use of effective fungicides. Net blotch is
showing strongest activity in the East and South west and is of concern after a wet April. Broad-spectrum treatments
at T1 should suppress net blotch but a further treatment is likely to be required in infected crops at T2 to protect
the upper leaves and ears. |
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Brown rust levels are relatively low and it has not over-wintered particularly well this season. It is still poised to
threaten crops in much of southern and central England if temperatures are high during late May and early June. T2
fungicides give large yield responses when brown rust develops strongly. |
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| Fig. 3 Regional foliar disease levels on leaf 2 |
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| Fig. 4 Regional foliar disease levels on leaf 3 |
| Eyespot and stem base diseases are present at modest levels this year. Eyespot was the most common disease affecting an average of 4.5% of stems nationally, whilst sharp eyespot and fusarium affected 0.6% and 2.3% of stems respectively. Highest incidence of eyespot occurred in the East Midlands and the North East/North West regions and sharp eyespot was highest in the South West. (Figure 5). Eyespot is an important disease on barley and control is advised where 20% or more tillers are affected. All the stem base diseases are likely to increase as the season progresses. For those crops where eyespot was present at GS 30 but not at the spray threshold, further crop inspection should have taken place at GS 31. |
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| Fig. 5 Regional stem base disease levels at GS30 |
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RAPID ACCESS TO THE LATEST REGIONAL CROP PEST AND DISEASE LEVELS |
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