1Department of Applied Plant Science, School of Agriculture and Food Science, Queens University Belfast and 2 Applied Plant Science Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, UK

Background and objectives
Northern Irish cereal farmers, in common with arable farmers from many other areas of Europe, have been experiencing a steep drop in grain prices. There has also been continuing pressure from environmentalists concerned with deleterious effects of crop chemicals. For both these reasons, research has been undertaken over the past 5 years on the effectiveness of applying fungicides to cereal crops at rates lower than those recommended by the manufacturers. Initial results have been reported [1, 2].

Materials and methods
Trials were set up on spring barley, winter wheat and winter barley, using cultivars susceptible to Erysiphe graminis, Septoria tritici and Rhynchosporium secalis, respectively. Trials commenced with spring barley in 1993, with the addition of winter wheat in 1994 and winter barley in 1995, with all three crops being further tested in 1996 and 1997. Trials were of factorial design with three replicates, the factors being fungicide type and rate of application. Fungicides were tested at the manufacturers' recommended rates and at half, a quarter and an eighth of these. There were also unsprayed controls. In 1997, the spring barley trial was modified to include one cultivar resistant to E. graminis and one which was susceptible. Individual diseases were assessed and yields, thousand grain and hectolitre weights calculated.

Results and conclusions
Results indicated scope for reduction in rates of fungicide usage, but this was crop-dependent. Thus even 1/8th rate fungicides gave useful disease protection and yield increases with spring barley, while with winter wheat the same rates gave negligible protection. However, although increased rates of fungicides gave relatively linear responses in disease control and yield gain with winter wheat, the yield increases at the highest rates were offset by the high cost of additional fungicide. As might have been expected, the use of a disease-resistant spring barley cultivar allowed for a greater reduction in fungicide rate than a disease-susceptible cultivar.

1. Mercer PC, Ruddock A, 1996. Proceedings, Crop Protection in Northern Britain, 1996, Dundee, pp. 109-114.
2.Mercer PC, Cooke LR, 1996. Home-Grown Cereals Authority Agronomy Update 1996, Section 7.