Yield, straw length, ripening, damage, grain composition and quality were determined on seven winter oat varieties included in trials grown in Northern Ireland between 1990 and 2000. Three management regimes were applied to the varieties in each year: (1) with fungicide but without plant growth regulator applications (+F−PGR); (2) with plant growth regulator and fungicide applications (+F+PGR); and (3) with neither fungicide nor plant growth regulator applications (−F−PGR). Disease control significantly improved yield, kernel content and the proportions of groats above 2·0- and 2·2-mm sieves but delayed ripening and increased the content of free kernels. Application of chlormequat significantly reduced straw length and the content of empty husks and increased the content of good oats but reduced kernel content. Specific weight, grain weight and the proportions of grain above 2·0- and 2·2-mm sieves were not significantly affected by either control of disease or application of chlormequat.

The combined effects of disease control and chlormequat significantly reduced leaning and brackling while lodging was reduced but not significantly. Rather than an increased incidence following disease control which was reduced by application of chlormequat, the two management strategies resulted in similar small incremental reductions in straw damage. In years with severe straw damage lower specific weight, grain weight and kernel content may have been attributable to the damage but quality was also poor in some years when there was little damage. Grain and groat size were only poor in those years when severe lodging or brackling occurred.

Year had the greatest influence on most characteristics and variety to a lesser extent. Disease control and to a lesser extent chlormequat application had smaller effects on fewer characteristics. While the effect of disease control on yield is of economic significance, the effect of chlormequat appears to be mainly of psychological significance.