The interaction of strobilurin fungicides with cereal varieties

Until the late 1990's cereal disease control in the UK had been almost entirely dependent on fungicides in tow chemical groups, the DMIs and the morpholines. With the registration of the first strobilurin fungicides in 1997, a completely new class of fungicide chemistry became available to growers. It had already been widely demonstrated that strobilurins could lead to substantial yield increases, in the order of 10-20 percent above those produced by conventional fungicides. However, very little was known about the variation in response of different cereal varieties. There was a clear need to re-evaluate the yield potential and responsiveness of varieties in the light of the new fungicides. In order to do this, the National Institute of Agricultural Botany (NIAB) grew five winter wheat and five winter barely trials at widely distributed sites in England and Wales in 1998. In each trial, six fungicide programmes were applied to ten contrasting varieties. Two of the programmes were based entirely on conventional fungicides and four on strobilurin fungicides, in combination with conventionals. The average yield benefit from strobilurin-based programmes compared with conventional programmes was 1.20 t/ha (13.6%) for wheat and 0.44 t/ha (6.7%) for barley. There was a positive response from all varieties, ranging from 0.77 t/ha (8.7%) to 1.61 t/ha (18.3%) in wheat and from 0.19 t/ha (2.9%) to 0.85 t/ha (13.0%) in barley. For winter wheat, the benefit of strobilurins was least for low yielding varieties with good resistance to disease, in particular to Septoria tritici. In the case of winter barley, varieties with susceptibility to net blotch showed a particularly large benefit from strobilurins. The relative yield of varieties differed slightly depending on whether or not strobilurins were included in the fungicide programme. It is concluded that if strobilurins were to be introduced into the fungicide programmes used in Recommended List trials, there would be slight changes in the ranking of varieties according to their fungicide-treated yield.