Feb. 24, 2015
Curtin University researchers are recommending growers and advisers carefully plan fungicide management strategies for net blotch in this season’s barley crops.
The warning comes on the back of their discovery of a thriving barley net-type net blotch (NTNB) population after tebuconazole treatment in WA samples.
Several mutations of NTNB fungus were found at the target site of the triazole fungicide (from the demethylation inhibitors – DMI - Group 3 fungicide group).
This has resulted in NTNB showing resistance to tebuconazole and some other triazole fungicides.
The discovery was made at the GRDC-supported Centre for Crop and Disease Management (CCDM), set up at Curtin University in 2014 to conduct cutting-edge crop disease research into genetics, breeding and fungicides.
CCDM fungicide resistance group program leader Dr Fran Lopez-Ruiz and research assistant Wesley Mair say their latest barley NTNB finding was made as part of an ongoing fungicide resistance analysis initiative, funded by GRDC at the CCDM.
Finding barley NTNB resistance
CCDM researchers exposed several foliar pathogens isolated from barley field samples to numerous active compounds and levels of resistance were measured.
Then, isolates showing an increased level of resistance were submitted to genetic analysis.
Dr Lopez-Ruiz says studies of pathogen mutations showed the target sites appeared to be changing shape, which consequently blocks the interaction with the fungicide.
He compared this effect to fitting a square peg in a round hole – a hole that was once square, but has now mutated into a round shape.
Due to the structural similarities existing between all triazoles, a low level of resistance has also been observed for two other triazole fungicides - epoxiconazole and prothioconazole.
Recommendations for fungicide treatments for NTNB in 2015
Net blotch reached damaging levels in WA barley crops last year, especially in high rainfall southern areas of the state.
CCDM researchers recommend that to minimise the risk of NTNB in the 2015 season, a range of fungicide and crop management strategies should be used, including:
-Reducing the risk of disease carry-over by avoiding sowing barley on barley stubble and instead introducing break crops
-Avoiding using barley varieties that are susceptible to NTNB in disease-prone environments. Baudin, Commander, Fathom, Litmus and Mundah are (among others) shown as susceptible in the Department of Agriculture and Food WA’s 2015 Barley Variety Guide for Western Australia
-Avoiding the use of tebuconazole on barley, as straight tebuconazole products are only registered for scald and powdery mildew on barley
-Using fungicide mixes that also contain a quinone outside inhibitor (QoI), as NTNB is unlikely to develop significant resistance to Qol. Examples include: Amistar®Xtra (cyproconazole + azoxystrobin) and Radial® (epoxiconazole + azoxystrobin) – note Custodia® (tebuconazole + azoxystrobin) is registered for suppression only of net blotch on barley
-If a second treatment is needed, using fungicides such as – Prosaro®, Tilt®Xtra and Opus® that are registered for NTNB in barley
-Always using the recommended label dose.
Check and act on suspected resistance
NTNB samples that are showing resistance to triazole fungicides at the CCDM centre came from WA and growers and advisers across all of the State’s rainfall zones are urged to watch closely for signs of resistance this season.
If fungicide resistance issues are suspected, contact the CCDM for testing and advice (see contact details below).
Impact of the resistance finding on WA’s barley industry
NTNB is a highly damaging disease that can cause substantial yield and quality losses in barley, especially in WA’s high and medium rainfall areas – but can also affect crops in lower rainfall zones.
Dr Lopez-Ruiz says if triazoles are over-used, without adequate anti-resistance measures, a similar scenario could occur in oat and wheat crops. Therefore, further research is needed to better determine the extent of this new issue.
He says it is not as straightforward as saying all NTNB populations are now resistant to tebuconazole, but a population has been identified that is resistant to some triazoles.
CCDM researchers will continue to work on determining the full extent of this issue to ensure that better resistant management strategies can be deployed to minimize its impact.
An overview of the centre’s activities and latest findings from some CCDM projects will be presented at the 2015 Agribusiness Crop Updates, hosted by GRDC and the Department of Agriculture and Food (DAFWA) at Crown Perth on February 24 and 25.
More localised information on this and other research will be provided at Regional Crop Updates, see www.grdc.com.au/Research-and-Development/GRDC-Update-Dates agric.wa.gov.au/regional-crop-updates-2015