| Monitoring of Diseases in Winter Barley at GS 30 (2005) |
|
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 fully-expanded leaf designated as leaf 1. The most popular cultivar was Pearl representing 50% of fields surveyed. Carat accounted for 18% of samples. Antonia accounted for 7% of samples and was the only other variety to exceed 5% of the total sample (Figure 1). |
 |
| Figure 1. Cultivars surveyed in spring 2005 |
|
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 levels of foliar disease were very similar to those recorded in 2004.
Mildew was the most severe disease in winter
barley nationally, affecting an average of 2.2% of leaf 3, whilst net blotch and rhynchosporium each affected
less than 1% of the area of leaf 3 (Figure 2). Brown rust was also recorded on leaf 3, affecting 0.1% of
leaf area. Mildew was also the dominant disease on leaves 1 and 2, affecting 0.2% and 1.3% of the leaf
area respectively. |
 |
| Figure 2. National foliar disease levels at GS 30 |
|
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 Yorkshire & Humberside 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. |
|
Powdery mildew has caused few problems in recent years, but has shown a greater increase in activity in spring over
the past two years. 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 3-4 years. Thus, mildew control is now dependant on specific
mildew products such as the morpholines, quinoxyfen and metrafenone. This year, there was markedly more mildew on the
top three leaves in the West Midlands than in other regions. This level of mildew on the top two leaves would justify
application of specific fungicides for mildew control. |
|
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 Midlands. 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. |
|
Brown rust levels are low and it has not over-wintered particularly well this season. |
 |
| Figure 3. Regional foliar disease levels on leaf 2 |
 |
| Figure 4. Regional foliar disease levels on leaf 3 |
| Eyespot and stem base diseases are present at modest levels this year. Fusarium was the
most common disease affecting an average of 4.5% of stems nationally which was in contrast to last spring when
eyespot was most often encountered. Eyespot and sharp eyespot affected 4.3% and 0.4% of stems respectively. Highest
incidences of eyespot, sharp eyespot and fusarium occurred in the North East/North West region (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. |
 |
| Figure 5. Regional stem base disease levels at GS30 |
|
RAPID ACCESS TO THE LATEST REGIONAL CROP PEST AND DISEASE LEVELS |
|
