Effects of strobilurin fungicide programmes and fertilizer nitrogen rates on winter wheat: severity of Septoria tritici, leaf senescence and yield

Four field experiments were conducted over 3 years to study whether adding a strobilurin fungicide to a triazole fungicide programme for disease control in winter wheat had any influence, in combination with different rates of fertilizer nitrogen (N), on the severity of foliar diseases, the degree of leaf senescence and consequently on yield. Septoria tritici was the dominant foliar disease observed in all experiments. The area under the disease progress curve (AUDPC) tended to be greater for untreated plots than those treated with fungicides; however, the performance of the programme containing a strobilurin fungicide did not always exceed that of the triazole-only programme. Fitting a quadratic equation to relationships between leaf N concentration and the proportion of leaf area covered with S. tritici on a relative scale across the four experiments indicated a possibility that there could be an optimum N concentration in host plants for S. tritici to develop, rather than a simple increase or decrease with a rise in plant N concentration. Plant height tended to be reduced following an application of a mixture of epoxiconazole and trifloxystrobin; however, it was not clear whether there was any association between plant height and the severity of S. tritici. S. tritici caused a reduction in mean grain weight (MGW) in most of the experiments. It was concluded that an optimum leaf N concentration may exist for S. tritici in winter wheat.