Barley growers throughout Western Australia should assess their integrated disease management strategies following detection of net form net blotch isolates with resistance to all three fungicide groups currently registered for control of this fungal pathogen.
Barley is WA's second-most important cereal crop after wheat, with the state's exports exceeding $1 billion in value per year. It is essential for the production of beer, a variety of food products, and as animal feed.
Uncontrolled infections of net form net blotch can dramatically reduce barley yields and grain quality. Fungicide groups 3, 7 and 11 are the only groups currently registered for managing this disease in barley. The detection of a number of isolates from South Stirling paddocks with mutations associated with resistance or reduced sensitivity to all three of these groups means fungicides may no longer provide reliable control.
The confirmation of triple resistance mutations in WA follows similar detections in barley growing regions of South Australia and Victoria. Researchers consider it likely that the triple-resistant isolates are already present in paddocks surrounding those where the infected samples were collected - and may also be present in other barley growing areas of WA.
This latest detection was made during analysis of infected barley samples by researcher Wesley Mair at the Centre for Crop and Disease Management (CCDM). The samples were collected from the South Stirling district by Department of Primary Industry and Regional Development (DPIRD) Senior Research Scientist, Kithsiri Jayasena as part of ongoing Grains Research and Development Corporation (GRDC) investments. He noted that significant disease was observed in a paddock of the popular barley variety RGT Planet (resistance rating MS-SVS), which was unable to be controlled by fungicide applications. An adjacent paddock planted with the newer Laperouse (resistance rating MRMS-MSS) was largely protected by that variety's improved disease resistance.
Associate Professor Fran Lopez-Ruiz, AFREN Project Lead at Curtin University, says the detection of highly fungicide resistant net form net blotch in South Stirling means WA barley growers should prioritise agronomic disease management. Photo: CCDM Communications Team
Associate Professor Fran Lopez-Ruiz, Project Lead for the Australian Fungicide Resistance Extension Network (AFREN), says the difference in impact between the RGT Planet and Laperouse paddocks highlights the importance of growers selecting barley cultivars with improved net form net blotch resistance.
"Varietal resistance is a cornerstone of integrated disease management as it denies the pathogen a susceptible host and helps keep infection levels low.
"Using agronomy to minimise disease pressure reduces reliance on fungicides during the growing season. This reduces fungicide use, slowing down the development and spread of resistance.
"Even using fungicides to control other diseases of barley can select resistance in any net form net blotch pathogens that are also present. The key to maximising the lifespan of fungicides is to leverage non-fungicide strategies to reduce disease levels."
GRDC Crop Protection Manager - South, Ruth Peek, says growers can help protect their barley yields by consulting with an agronomist about fungicide options for their local area and eliminating 'green bridge' volunteer barley over summer.
Growers should also prioritise planning more non-barley rotations and adopting agronomic disease management practices including rolling or grazing barley stubble to reduce disease pressure.
All growers wanting to avoid the selection of fungicide resistant diseases in their crops should follow the disease management principles of AFREN's Fungicide Resistance Five: 1) avoid susceptible crop varieties; 2) rotate crops and varieties; 3) use non-chemical control methods; 4) spray strategically and only if necessary; and 5) rotate and mix fungicides groups.
AFREN is a Grains Research and Development Corporation (GRDC) investment to promote best practice management strategies for reducing the impact and emergence of fungicide resistance.
