Mixing fungicides matters
By Brandy Rawnsley
Fungicide resistance occurs when a fungal pathogen is no longer controlled effectively with the use of a fungicide from a particular mode of action (MoA) group eg a Group 11 (Strobilurin). In any population, there are likely to be a small percentage of fungi that have a degree of natural resistance and are less susceptible to the fungicide application. After repeated use of a particular fungicide MoA group those that have this natural resistance will survive and flourish, leaving an entire population that is now resistant to that fungicide MoA group.
We may understand the concept of resistance, but do we know how to manage it?
Firstly, refer to the product label as it is easier to misuse fungicides than you may think. Behind every label is a great deal of research, which has determined the most effective rate and ideal application intervals to achieve optimum control.
Secondly, rotate the fungicide products with a different mode of action to prevent over-use of one group. With fungicides, when you’re on to a good thing, don’t stick to it!
Thirdly, mixing fungicides with different modes of action reduces the risk of developing fungicide resistance. A fungal pathogen that has survived one fungicide is more likely to be eradicated by the other.
Mixing fungicides can be either tank-mixing products or using co-formulations of fungicides with a different mode of action (providing that both of the different fungicide groups offer effective control of the pathogen at the applied rate).
Fungicides that target the powdery mildew fungus, Erysiphe necator, should all be applied preventatively, with restrictions on the number of fungicides used within the same group. For example, SDHI fungicides such as MIRAVIS® (group 7) should only be used consecutively when applied in a mixture with a fungicide from a different group such as THIOVIT JET® (group M2).
When targeting Botrytis grey mould, it is recommended that three different groups of fungicides are used if more than three sprays are applied. In this instance, use SWITCH® (a mixture of group 9 and 12) at 80% capfall, then AMISTAR® (group 11) later in the season to reduce the risk of resistance developing.
For further information about resistance management strategies visit www.croplife.org.au or speak to your local Syngenta representative.
Dr Belinda (Brandy) Rawnsley is a Syngenta Technical Services Lead for Viticulture and Horticulture