Testing the effectiveness of fungicides against myrtle rust – what worked best?

March 23, 2020

Using an artificial inoculation protocol, the efficacy of eight fungicides* were applied as curative or protectant treatments against myrtle rust on two native New Zealand species – New Zealand ‘Magic Dragon’ (Lophomyrtus x ralphii) and pōhutukawa (Metrosideros excelsa).

The impact of rate (x2), frequency (single or double) and timing (pre- or post-inoculation) of fungicide application were investigated.

The results

  • overall, the most effective fungicides tested across both species were those that included a demethylation inhibitor and strobilurin mix, notably tebuconazole and trifloxystrobin (Scorpio®) and cyproconazole and azoxystrobin (Amistar Xtra®)
  • these fungicides significantly reduced infection of host plants relative to the water control
  • timing of application significantly affected bioefficacy, with applications made 7 days before inoculation or 7 days after inoculation being generally the most effective
  • the rate of fungicide application was not significant for both host species with few interaction terms showing overall significance


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*Fungicides trialled:

  • tebuconazole/trifloxystrobin
  • cyproconazole/azoxystrobin
  • fosetyl aluminium
  • triforine
  • triadimenol
  • oxycarboxin
  • copper
  • tebuconazole  



March 2020