Central Science Laboratory MAFF, Sand Hutton, York Y04 1LZ, UK

Background and objectives
Fungicides are the most important group of pesticides used throughout agriculture and horticulture in Great Britain. In 1996 they accounted for 43% of all applications by area treated, with herbicides accounting for 33%, insecticides 13% and other pesticides 11%. Winter wheat dominates arable cropping, and with almost 2 M ha grown in 1996 [1], represented the single most important crop for fungicide inputs. Foliar applied fungicides accounted for over 8.1 M formulation-treated hectares [2], while fungicidal seed treatments were used on a further 2 M ha. However, within the past 25 years, spraying practices have developed from a situation where none of the crop was treated with foliar applied fungicides in 1970, to over 97% of the entire crop treated currently. This paper examines the changes in fungicide spray programmes and practices that have occurred in recent years on winter wheat.

Materials and methods
Data for England and Wales from the Pesticide Usage Survey and the Cereal Disease Survey databases, maintained at the Central Science Laboratory, were analysed to identify major trends and changes in fungicide use on winter wheat since 1970. Variations in area treated, number of sprays used, composition of tank-mixes and rates of application over the period 1970-96 were examined, and the factors influencing any changes investigated.

Results and conclusions
In 1970, no recommendations for the use of foliar applied fungicide sprays on wheat existed, and the crop was invariably untreated. Such fungicides were first recommended for use on winter wheat in 1975 under the Agricultural Chemical Approvals Scheme (ACAS), though the earliest official record of their use was in 1973 when an estimated 1% of the crop was treated. This proportion increased gradually and by 1981 80% of the crop was treated, with two-spray programmes being used for the first time. Since 1990, over 97% of the crop has been treated annually, with many crops receiving two or more sprays. In 1996, 47% of crops received a two-spray programme, 30% three sprays and 11% four or more applications. However, the trend away from label-recommended rates to reduced-rate applications has significantly influenced the total amount of fungicide applied. The mean dose applied per fungicide product in 1988 was 0.9 of label recommended rate whereas by 1996 this had fallen to 0.5. During the same period there has been an increase in the number of products applied within a spray to broaden the spectrum of activity. In 1988, 67% of sprays applied consisted of a single product and 31% contained two, whereas in 1996, 39% of sprays contained a single product, 43% contained two products and 16% contained three. This was also accompanied by a concurrent increase in the availability of formulated mixtures, resulting in an increased number of active substances (a.s.) applied per spray from an average of 1.8 in 1988 to 2.3 in 1996. Significant improvements in the timing of fungicide spray programmes have also occurred over this period. However, a number of spray applications are still made at inappropriate times during the growth of the crop, and there is clearly potential for both reductions in use and optimization of use by refining spray timing alone. As a result of the trend towards decreasing dose and the introduction of active substances effective at lower rates of application, the weight of fungicide applied has decreased from 1.63 kg a.s./ha grown in 1988 to 1.12 kg a.s./ha in 1996. Increased awareness of farmers in their use of fungicides has also led to a significant reduction in the level of misuse. In 1996, non-approved use of fungicides was not encountered on any of over 6850 fields surveyed. Though patterns of fungicide use have been more predictable during recent years, the introduction of new chemistry, coupled with potential changes in environmental and support-level policy, may radically change this in the near future. Official monitoring will continue to examine how efficiently farmers adopt and utilize new strategies for disease control under such changes.

1. Thomas MR, 1997. Pesticide Usage Survey Report 100. MAFF, London.
2. Thomas MR, Garthwaite DG, Banham AR, 1997. Pesticide Usage Survey Report 141. MAFF, London.