Update on Septoria resistance to strobilurin type (QoI) fungicides
Septoria tritici is the most economically important pathogen of winter wheat in Ireland. When weather conditions are suitably wet and conducive to its spread, yield losses of up to 40% can be experienced. Wheat growers in Ireland have used any means at their disposal to control this potentially devastating disease. The strobilurin fungicides and other QoI products were quickly adopted into the growers' armoury to combat this disease and have been used to good effect for the past 5 or 6 years. However, the results of a Teagasc nation-wide survey (using highly sensitive PCR technology) carried out in February 2003, confirmed that Septoria tritici resistance to strobilurin type fungicides was widespread. The levels of resistance varied, but testing of Septoria tritici isolates confirmed that most sites displayed moderate to high levels of resistant isolates. In general, sites displayed a range of resistance levels, with an average level of about 50%. The Pesticide Control Service (PCS) undertook an urgent review of the registrations of strobilurin type products and imposed certain restrictions on the use of these products in a concerted effort to prolong the useful life of this very valuable and effective group of chemicals. As part of the review of the strobilurin type registrations, companies were requested to provide the PCS with Septoria tritici monitoring data for the 2003 growing season. This data has been reviewed and evaluated and the following decisions have been taken
- Products containing only strobilurin type active substances can no longer be relied on to give effective control of Septoria tritici.
- If using a product containing both a strobilurin type active substance and another active substance with a different mode of action for the control of Septoria tritici, the content of the other active substance must be at a level sufficient to control the disease (e.g., if there is only half rate triazole in the product then this will not be sufficient to control Septoria tritici and additional triazole must be added)
The PCS will continue to closely monitor the use of strobilurin type products during the coming growing seasons. The PCS will maintain close contact with manufacturers, advisory services and growers with a view to detecting cases of resistance, shifts in target organism sensitivity to these products and evaluation of the results of monitoring programmes.