Response of winter wheat and winter barley varieties to strobilurin fungicides

Abstract

Until the introduction of the strobilurin fungicides in the late 1990s, cereal disease control had been almost entirely dependent on 'conventional' fungicides in the DMI and morpholine groups of chemistry. Although there was evidence of substantial increases in yield resulting from the use of strobilurins, very little was known about the interaction of varieties of wheat and barley with the new chemistry. This project addressed the question of whether all varieties are likely to benefit equally from strobilurins or whether some are likely to benefit more than others and looked at the implications for the evaluation of varieties in Recommended List trials.

Five winter wheat and five winter barley trials were grown 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, one of these being the programme used by NIAB in Recommended List trials that year. The other four programmes were based on strobilurin fungicides, in combination with conventionals.

In wheat there was evidence of improved control of Septoria tritici where strobilurins were included in the programme. In addition, the strobilurin fungicide Amistar gave good control of certain pathogens on the ear, in particular Septoria nodonun, the cause of glume blotch and Microdochium nivale. In the barley trials, strobilurins improved the control of Net blotch, but were generally less effective againstRhynchosporium. Strobilurin-based programmes tended to increase the percentage of the leaf area remaining green. This effect, which was apparently partly independent of disease control, was not detected until around GS75 and then mainly in the lower leaf layers.

The average yield benefit from strobilurin-based programmes compared with conventional programmes was 1.20 t/ha for wheat and 0.44 t/ha for barley. There was a positive response from all varieties, ranging from 0.77 t/ha to 1.61 t/ha in wheat and from 0.19 t/ha to 0.85 t/ha 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 changes in the ranking of varieties in order of fungicide-treated yield. However, these changes are likely to be relatively minor and the evidence supports the view that varieties are unlikely to move from the lower part of the ranking to the upper part, or vice versa.