Are multi-site fungicides now essential, not optional?
MULTI-SITE fungicides may not have the same level of activity against key wheat disease septoria tritici as triazole and SDHI actives, but disease experts gathered at a resistance meeting last week took the view that now was the time to assign them equal importance within a fungicide programme.
ADAS senior research scientist Dr Jonathan Blake said he would like to see multi-site fungicides such as folpet and chlorothalonil used as a matter of course at the T1 and T2 fungicide timings. Septoria tritici was becoming less sensitive to triazoles and SDHIs also needed protection against resistance development.
Multi-site fungicides did not provide the same intrinsic level of activity against septoria as both of these groups, but offered a decent level of protectant activity, he said.
New modelling work on fungicide mixture strategies being undertaken by ADAS and Roth-amsted Research indicated that even a very low dose of a low resistance risk active ingredient - a multi-site - increased the life expectancy of a higher resistance risk partner such as a triazole or SDHI.
Broom’s Barn director Bill Clark warned triazole efficacy was going to continue to drift. “You don’t get crops green to the floor with just triazoles any more. We can’t control septoria in high risk situations with triazoles alone,” he said.
The story surrounding the genetic mutations that conferred resistance to triazole fungicides within the septoria tritici population was a complicated one and, so dynamic was the situation, that knowing what mutations were present in a population one year was no guide to what might be present the following year and was of limited practical value.
Like triazoles, SDHIs were active at a single site within the septoria fungus; the resistance risk was medium to high and resistance management was needed to protect their activity, said Mr Clark.
“There is a hint SDHIs are not all the same in terms of the development of resistance, but they are similar. All I am hoping is that if and when they are affected by resistance - and they will be - it is not to the same degree for each.”
In cereals, use of mixtures of triazole/triazole, triazole/SDHI or multi-sites were the only way to protect fungicide activity against septoria.
Agrii (formerly Masstock UAP) technical support manager Malcolm Smith said the organisation’s approach to resistance management was to manage crops to prevent disease, rather than to cure it. He urged growers to pay particular attention to getting the timing and dose of fungicide applications right.
Commenting on the Irish situation, John Spink of Teagasc said most septoria tritici strains remained sensitive to at least one of the triazoles, but strains with reduced sensitivity to all triazoles were increasingly present in the Irish septoria population.
No incidences of resistance to SDHIs had been detected in Ireland, but this group of fungicides must be protected, he said.
Providing a fungicide manufacturer’s perspective, Stuart Hill of Makhteshim Agan UK said multi-site fungicides such as folpet (Phoenix) had a vital role in protecting the efficacy of triazoles and SDHIs and should not be seen as ‘second division’ products.
He suggested there was a need to rethink fungicide programmes to make them more protectant in nature. Key fungicide timings were unlikely to change, he said, so would one solution be to use multi-site fungicides such as folpet at each key stage of a fungicide programme?
- Use a wide range of active ingredients with differing modes of action on target diseases
- Consider using mixtures of azoles as this may help slow down further shifts in sensitivity eg Brutus/ Kestrel/Prosaro
- Use tank mixes or formulated mixes with differing mode of action
- Use new active ingredients as soon as they are launched (subject to positive trials data) to get the greatest benefit from them
- Adhere to label restriction on number of applications
- Make appropriate use of multi-site fungicides as these have the lowest resistance risk