Source: Grains Research & Development Corporation Australia (GRDC) [edited]
New South Wales [NSW] and Victorian growers are urged to be on alert following confirmation that difficulties experienced in 2020 controlling wheat powdery mildew are linked to resistance of the pathogen to demethylase inhibitor (DMI, Group 3) fungicides. Fungicide resistance was detected at frequencies ranging from 50 to 100 per cent. This marks the 1st time that resistance in wheat powdery mildew to DMIs has been detected in Australia.
Researchers from the Fungicide Resistance Group at the Centre for Crop and Disease Management (CCDM) confirmed the presence of DMI resistance in a range of samples sent by agronomists who were concerned about disease levels in wheat crops during the 2020 season. The samples from across NSW and into Victoria were from predominantly Vixen and Scepter bread wheat varieties, and a lower number of durum wheat varieties.
NSW Department of Primary Industries Steven Simpfendorfer is not entirely surprised some level of resistance was detected, but is surprised by the high frequency. He describes the detections as alarming and a wake-up call for industry. "These detections have occurred predominantly in high-value, irrigated cropping regions, which create ideal conditions for disease development," [he] says. The reliance on DMI fungicides by many growers over many years contributed to selecting for the fungicide resistance.
CCDM's Steven Chang says genetic and phenotypic analyses of the isolates showed a combination of mutations in the DMI target gene. Additionally, all samples had some level of strobilurin (Group 11) resistance. All growers need to implement fungicide resistance management strategies to maximise chances of effective and long-term disease control. The Australian Fungicide Resistance Extension Network (AFREN) suggests an integrated approach tailored to local conditions.
[Powdery mildew (PM) of cereals and other grasses is caused by the fungus _Blumeria graminis_, currently the only species in the genus. Different pathovars have been designated for different cereal hosts, with f. sp. _tritici_ affecting wheat and triticale; f. sp. _hordei_ affecting barley; f. sp. _avenae_ affecting oats; f. sp. _secalis_ affecting rye. The pathogens affect all aerial parts of the host. Humid conditions allowing the disease to reach the flag leaf, as well as external factors that encourage heavy tillering favour disease development and increase yield losses in grain crops.
Powdery mildews are a group of fungi causing similar symptoms on a range of host plants. The group includes many species in a number of genera. Generally, each fungal species is confined to a number of host species it can affect. Leaves are covered with white mycelium; heavy infection leads to reduced photosynthetic ability and thus decreased plant vigour. The pathogens can cause serious losses in many important crops including vegetables, cereals, grapevine, hops, oilseed rape and sugar beet. Spores are spread mainly by splashing rain, wind or mechanical means. Management strategies for these pathogens generally include cultural practices to reduce inoculum, fungicides, use of clean seed and resistant cultivars.
Demethylase inhibitor (DMI; also called azole or sterol biosynthesis inhibitor) fungicides are the largest class of fungicides. They were introduced in the 1970s and new products continue to be introduced. Strobilurins are strongly antifungal agents produced by fungi. Being derived from natural products, they are considered environmentally safe but, like several other fungicide classes, they have single-site activity and therefore pathogen resistance is of major concern worldwide. Integrated disease management, including varying crops or crop cultivars in time and space, as well as rotating or mixing chemical classes of fungicides is vital to extend the useful life of host resistances and agrochemical compounds.
In Australia in 2020, higher than expected levels of powdery mildew were also reported in barley from Queensland (see link below), but it is unclear whether any new strains are thought to be involved there.
Australia (with states):
Powdery mildew on wheat:
Additional news stories (subscr):
Barley PM increase Queensland:
Information on powdery mildews of cereals:
_B. graminis_ taxonomy and synonyms:
Information on DMI fungicides:
Information on strobilurins:
History and review of agricultural fungicides: