Protecting
the efficacy of azoles and SDHIs against the development of resistance by
Septoria should remain a key part of spray programmes, according to guidelines
from the UK Fungicide Resistance Action Group (FRAG).
Over the
last three years, HGCA-supported research has looked at the best way to
maintain azole and SDHI performance in the years ahead. Researchers have done
field experiments to test the best SDHI + azole mixtures for anti-resistance
strategies.
In
general, spray programmes need to balance the need for good control with
appropriate practices to minimise resistance risks to azoles and to SDHIs. In
practice, this is challenging as both groups of actives are at high risk of
losing efficacy, while the UK climate is conducive to Septoria.
Selection
for azole resistant strains is driven mainly by the number of applications
rather than the dose, so programmes should aim to use the minimum number of
applications necessary. At the core treatment timings of T1 and T2, robust
azole rates will maximise control and protect any SDHI partners from
resistance.
At other
timings, alternatives to azoles should be considered, depending on the
situation in the field. For example, consider using multi-site inhibitors at T0
for Septoria protection or strobilurins against rusts. Using azoles at
additional timings – T1½ and T4 – will increase selection for resistant
strains of Septoria.
For SDHI
resistance, selection is likely to be increased both by dose and the number of
treatments. As a result, it is important to use the minimum SDHI dose and
number of treatments for effective control. Partnering with a robust dose of
azole will reduce SDHI resistance risk without markedly increasing selection
for azole resistance.
Throughout
Septoria control programmes, it is important to use a range of modes of action
and maximise the use of multi-sites which have a low resistance risk, to
protect azoles and SDHIs and prolong their useful lifetimes.
A longer summary of azole and SDHI
stewardship from FRAG is available at hgca.com/disease
The Global Miller
This blog is maintained by The Global Miller staff and is supported by the magazine GFMT which is published by Perendale Publishers Limited.
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