Would you like the good news or the bad news first?
The bad news right? To get it over with?
The bad news is, after analysing 115 barley paddock samples from southern WA, Group 3 (DMI) fungicide resistance in net blotch – both spot form and net form – is everywhere. Not in every sample, but prevalent enough to be a problem for all of southern WA.
And to add fuel to the fire, we now know this problem is growing.
Now for the good news.
CCDM researchers have worked with Southern WA growers to improve the understanding of fungicide resistance in the landscape. Using phenotype testing (explained further down) we have shown that fungicide resistance is highly varied in Southern WA.
For the second year running our Barley Disease Cohort Project and the growers who are part of it have allowed us to put together a comprehensive picture of Group 3 (DMI) fungicide resistance in a grain growing region.
A map of fungicide resistance in the net blotches
In 2020 and after full fungicide programs were applied, growers from southern WA collectively sent in 115 samples of diseased leaves to CCDM. Our researchers then grew fungal cultures from the leaves and tested them for fungicide resistance.
This map shows where the highest level of DMI fungicide resistant phenotypes (see explainer in next section) of spot form net blotch (SFNB) and net form net blotch (NFNB) were detected.
Distribution of phenotypes for both NFNB and SFNB in 2020.
Let’s explain what we mean by Resistant, Reduced Sensitivity and Sensitive Phenotypes
Out of all the diseases of interest here at the CCDM, both forms of net blotch are probably our most complex. This complexity has led us to develop a phenotype test for testing for fungicide resistance to Group 3 fungicides.
Phenotype describes the observable properties or traits of an organism. By observing how NFNB or SFNB fungal pathogens grow across a concentration gradient of fungicides in our labs, we can diagnose the growth of each fungal sample as one of three phenotypes:
Sensitive: A sensitive phenotype means Group 3 fungicides should still work okay.
Reduced sensitivity: A reduced sensitivity phenotype means Group 3 fungicides may still work okay at controlling net blotch, but not as well as they would on a sensitive population. You still have management options, however reduced sensitivity populations are also at greater risk of becoming fungicide resistant if you continue to use these actives.
Fungicide resistant: A fungicide resistant phenotype means some Group 3 fungicides will not likely control these pathogen populations, and therefore should be avoided.
From 2019 to now
Since 2019, the Barley Disease Cohort Project has enlisted 205 growers, mostly from southern WA. Over the past two years these growers have sent in diseased barley leaf samples that have been tested for fungicide resistance.
In 2019, we collected any diseased sample at any time.
In 2020, we only collected after a full fungicide program was applied.
In 2021, we’ve used a more targeted approach to our sample collection.
Our team are now working on 2021 samples that have been collected from areas with high levels of resistance. In doing so we are seeking to understand more about both the short and long term paddock history and the potential contribution of management decisions to the development of fungicide resistance.
The team have also completed a series of large scale field trials aimed at examining the impact of within-season fungicide application on the spatial distribution of disease and fungicide resistance at a sub-paddock scale. Stay tuned for these results!
