1Central Science Laboratory, Sand Hutton, York YO4 1LZ, UK; 2ADAS Rosemaund Research Centre, Preston Wynne, Hereford HR1 3PG, UK

Background and objectives
Annual cereal disease surveys have been conducted since 1970 for winter wheat [1] and since 1981 for winter barley [2] and, combined with up-to-date research on disease epidemiology and crop-loss assessment, now provide an extensive database on the economic importance of particular diseases in relation to seasonal or cropping effects, cultivars and commonly used fungicide programmes. The objectives of the surveys are to monitor the annual incidence and severity of cereal diseases and to identify national and regional in-season, cross-year, meteorological, husbandry and pesticide relationships.

Materials and methods
Approximately 300 crops each of winter wheat and winter barley were monitored annually. The fields were selected at random from a list of farms stratified by region from annual returns to MAFF Census Branch. Additional samples were taken from Wales to obtain more reliable estimates of disease severity. Crops were sampled by collecting 50 fertile tillers at random from a diagonal transect of the field. Winter wheat was sampled from the early to medium milk development stage (GS 73-75) and winter barley from the watery ripe to early milk development stage (GS 71-73). Foliar diseases were assessed using standard area diagrams. Stem-base diseases were ascribed to different categories. A comprehensive questionnaire was used to obtain details of cultivar, sowing date, previous cropping and pesticide use for each crop sampled. All data collected were entered into an INFORMIX relational database.

Results and conclusions
Septoria tritici has been the dominant disease of winter wheat since 1984, being recorded at 3.2% area leaf 2 in 1997. Mildew (Erysiphe graminis) and Septoria nodorum are relatively minor diseases, being recorded at less than 1% area of the second leaf during the past 6 years. Yellow rust has been recorded only at less than 0.05% area leaf 2 since 1990, when it reached 0.2% nationally. Examination of regional trends showed that S. tritici tended to be more severe in the south-west and Wales, although levels were also consistently high in the south-east.

An interesting feature of the winter barley survey has been the steady decline in the severity of mildew from 4.8% area leaf 2 in 1991 to 0.5% in 1997. Net blotch has become the dominant disease of winter barley since 1990, reaching a peak at 3.4% in 1996 to fall to 2.2% in 1997. Net blotch tended to be more severe in the east and north, although there were occasional high levels recorded in the south-west. Rhynchosporium leaf blotch was more common in the south-west.

It has been found that in many cases fungicides were not being used cost-effectively or at the optimum timing. In winter wheat, despite changes in disease severity from year to year, the use of fungicides in terms of the number of sprays applied to the crop has remained fairly constant, fluctuating only between 1.9 and 2.2 sprays per crop in a season. The pattern for winter barley was very similar, the number of sprays varying from 1.3-1.7 per crop for the same period. This was an indication that farmers were paying little attention to disease risk in a given season, but were applying sprays as routine insurance.

One of the benefits of surveys is that it is possible to monitor the effect of advice or changes in policy on diseases levels and inputs. In the mid-1980s there was a change in advice to switch the main spray, which was applied at ear emerged (GS 59) for control of diseases of winter wheat, to flag leaf emerged (GS 39). Meaned across all farm types, the data on spray timing indicated that this advice began to take effect fully only in 1994. With winter barley, sprays tended to be applied according to current advice, with the main period being at first node (GS 31). A few crops were sprayed in the autumn, although this was generally discouraged as being unnecessary except in special circumstances, such as very susceptible cultivars grown on light soils.

1. Polley RW, Thomas MR, 1989. Annals of Applied Biology 119, 1-20.
2. Polley RW, Thomas MR, Slough JE, Bradshaw NJ, 1993. Annals of Applied Biology 123, 287-307.