Resistance problems discovered with wheat powdery mildew fungicides

GRAIN growers are being advised to implement effective integrated disease management strategies following the discovery of resistance to strobilurin fungicides in wheat powdery mildew (WPM).

The resistance was found in 2016 crop samples from Victoria and Tasmania by the Fungicide Resistance Group at the Centre for Crop and Disease Management, a national research centre co-supported by Curtin University and the Grains Research and Development Corporatio.

The researchers confirmed the WPM mutation associated with the recently discovered strobilurin (Group 11, QoI fungicides) resistance is G143A, a mutation well known throughout other parts of the world but until now previously undetected in Australia.

In European countries, WPM sensitivity to QoI fungicides was lost within two years of the introduction of this class of fungicide and was due to the G143A mutation.

But scientists say there is still some hope for Australian growers, given the strobilurin resistance was detected early.

“If we act now, we will have more chances of maintaining the efficacy of this group of fungicides for as long as possible,” says Dr Fran Lopez-Ruiz, leader of the FRG at the CCDM. “To do this, growers need to be mindful about what they are spraying on wheat crops.”

He says only two modes of action are registered for WPM control – group 3 (DMI) and group 11 (QoI) fungicides, which are already sold in mixtures with a DMI, such as azoxystrobin and epoxiconazole.

“For WPM, there is currently a high reliance on DMI and QoI fungicides for disease control. With strobilurin resistance in WPM we will have to minimise our use of QoI fungicides,” Dr Lopez-Ruiz says.

“We advise only one QoI spray per year as the only way forward in keeping disease populations from developing very fast widespread resistance to this mode of action.”