4.9.19
ANALYSES OF FUNGICIDE OPTIMIZATION POTENTIAL IN ENGLAND AND WALES THROUGH EXPLOITATION OF WHEAT CULTIVAR DISEASE RESISTANCE

JA TURNER and MR THOMAS

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

Background and objectives
The decision-making process facing a farmer in the selection of fungicide spray programmes in the UK is now a very complex one. Farmers have a wide choice of products and mixtures which may be applied at a range of doses and timings. Inputs must be tailored to seasonal disease pressure and the cultivar selected in order to achieve economic disease control. However, analyses of the MAFF Winter Wheat Disease Survey database have shown that farmers are not fully utilizing the inherent genetic disease resistance of cultivars in selecting fungicide inputs [1]. Experimental evidence shows that total dose optima differ between resistant and susceptible varieties and that optimum inputs relate to the potential yield response of the individual cultivar. Further investigation has been undertaken in order to identify, more specifically, factors influencing fungicide inputs to different cultivars. This paper reports the results of the influence of farm size on inputs.

Materials and methods
The Pesticide Usage Survey database, which contains data collected biennially from over 7000 wheat crops in England and Wales, was analysed to investigate fungicide inputs to five cultivars of winter wheat for 1996. The cultivars selected, Riband, Brigadier, Hereward, Hunter and Hussar, accounted for over 70% of the planted area of winter wheat in England and Wales and represented a range of genetic resistance to disease [2]. Riband was the most susceptible cultivar, with Hussar and Hunter the most resistant. The influence of arable farm size (the area of all arable crops excluding grass and set-aside) was investigated. Farms were divided into four size groups according to area of arable crops grown: <100, 100-150, 150-250 and >250 ha.

Results and conclusions
An analysis of cultivar profile on farms showed that Riband and Brigadier were the most commonly grown cultivars. The percentage area of Brigadier grown was highest on smaller farms and decreased with increasing farm size, whilst the proportion of Hussar was highest on farms over 250 ha. Data on the mean number of sprays applied to each cultivar show that on the largest farms the level of inputs was most closely related to the resistance of the cultivar. Therefore, a susceptible cultivar such as Riband received a relatively higher number of sprays than the more resistant Hunter or Hussar. Differences between inputs to different cultivars decreased with decreasing farm size. Farms over 150 ha applied the highest number of sprays to Hereward, a high-value milling wheat. Farms in the 100-150-ha group showed the least differentiation between cultivars. Similarly, the total dose applied to cultivars on farms in the 100-150-ha group also showed the least differentiation between cultivars. Total dose inputs on farms above 150 ha were highest on Hereward, again reflecting its value, and showed the most differentiation between cultivars. The average fungicide dose applied decreased with increasing farm size, with profiles of cultivar management differing markedly between size groups.

The evidence suggests that farmers with the largest arable areas (>250 ha) follow current advice on cultivar management more closely than those with smaller farms. These farmers are likely to have the most access to advice from consultants and to be targeting the quality wheat market. They are also likely to have the most flexibility in fungicide application and cost. The smallest farms may have less flexibility and are more likely to grow a single cultivar throughout the farm. Medium-sized arable holdings may have more diverse cropping, and management of individual wheat cultivars may not be a priority. The analyses carried out have identified one area where fungicide use on different cultivars could be optimized. If farmers with farms of less than 100 ha, which account for 34% of the total wheat area, adopted strategies currently used by the larger farms, the overall saving would be in excess of 1.2 M. Future work will aim to investigate further factors influencing fungicide and insecticide use on farms and to compare cultivar management within individual farms.

References
1. Stevens DB, Turner JA, Paveley ND, 1997. Aspects of Applied Biology 50, 279-284.
2. Anon., 1997. National Institute of Agricultural Botany, Cambridge, UK.