Despite widespread resistance to strobilurins in the S. tritici population, they still give some control of the disease and there is a clear dose-response to use. The graph below shows the mean level of activity of Vivid (pyraclostrobin) compared with other standards. At full dose Vivid gave about 30% control of the disease.
Contrast this level of activity against S. tritici with the control of brown rust given by strobilurins in the graph below. There is no resistance to strobilurins in the brown or yellow rust populations and the level of control is very high – at least as good as the best azoles. The second graph also shows how the addition of a strobilurin (fluoxastrobin) to Proline in the formulated mixture Fandango improves the rust activity (compare Proline alone with Fandango). The rust activity of the strobilurins is important at the flag leaf timings and in ear sprays where brown rust control can be very important, especially on varieties such as Alchemy.
The strobilurins can still produce greening effects that can result in additional yield responses over and above azole or azole/Bravo spray programmes. Predicting where and when such yield responses are likely is difficult but in general there is still a place for strobilurins in the fungicide programme – giving some control of septoria but still giving high levels of control of other diseases and often delivering economic yield responses.
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