Three words…
1st word: ______ Bix
2nd Word: Rhymes with louder-y
3rd word: What bathrooms love.
If you guessed wheat powdery mildew, well done!
At CCDM we named this disease the trickiest disease to manage in 2022, due to the number of industry members contacting us about fungicide resistant wheat powdery mildew throughout the season.
CCDM’s fungicide resistance expert Fran Lopez-Ruiz said unfortunately in the case of wheat powdery mildew, besides WA, everyone who sent in a sample to CCDM suspecting fungicide resistance, they each received a confirmation they had it.
“So, yes, it’s been a big issue, it’s been bothering the industry and unfortunately it’s going to be an ongoing problem, at least in the medium term,” Fran said.
More about the spread of the resistant genotype of wheat powdery mildew
Fran said there is a resistant genotype that is spreading very quickly throughout the Eastern States growing regions, including NSW, Tasmania, South Australia and he’s pretty certain it’s widespread in Victoria too.
He said growers with this resistant genotype in their paddocks, will see little or no control from some Group 3 fungicides (DMIs), such as propiconazole, or any Group 11 fungicides (QoIs).
“And this, combined with very conducive conditions for the disease in 2022 has led to a lot of trouble for growers and, unfortunately, the disease will continue to be a problem for as long as there is highly infected stubble from previous seasons,” Fran said.
He said samples received from WA have remained free of fungicide resistance so far, however to keep it that way, growers need to be very careful with their management of this disease, as it has a very high risk of developing resistance.
Conducive conditions can be misleading
While most samples sent in to CCDM labs were mostly fungicide resistant, Fran said samples from WA were not, even though there were many reports of fungicides not working.
Fran said when the conditions are perfect for disease development, and disease is rife, even the best chemical compound available will not control disease properly, which can sometimes seem like fungicide failure.
“And this is because the compound is not a silver bullet, it’s not going to make the disease go away. Where disease levels are high and the conditions are perfect, growers need to assume that fungicides may not bring the expected level of control, you’ll still see disease in paddock.
“This is why there were many situations in 2022 where fungicides were less effective than expected – it was not resistance, it was just too much for the fungicide to deal with, and the fact that we saw this across all crops – especially on wheat and barley – supports this point.”
CCDM fungicide resistance expert Fran Lopez-Ruiz
What options are left for growers?
Fran said at the moment, growers need to manage the resistant disease culturally as best as possible, and only resort to fungicides as a final option.
“While industry is looking at alternative varieties or alternative fungicide treatments, in the short term growers will need to grow more resistant varieties where possible and try to deploy longer rotations, and link in with the information published by AFREN,” he said.
Non-chemical management tips from AFREN Wheat Powdery Mildew Fact Sheet
While the season draws to an end, there are still some management tips to think about to set up for 2023. These are straight from the Australian Fungicide Resistance Extension Network (AFREN) Fact Sheet for managing wheat powdery mildew, and are relevant for the next few months:
Planting less susceptible wheat varieties: Any level of genetic resistance to wheat powdery mildew will help slow the rate of pathogen and disease development within a crop. This, in turn, reduces the reliance on fungicides for managing the disease.
Inoculum management: Eliminating volunteer wheat plants during fallow periods and reducing infected stubble loads through grazing, rolling, etc, will reduce the volume of spores spreading into an adjacent or subsequent wheat crop.
Practicing good crop rotation: A program of crop rotation creates a dynamic host environment that helps reduce inoculum levels from year to year. Rotating non-susceptible wheat varieties can also provide a more dynamic host environment, forcing the pathogen to adapt rather than prosper.
Avoiding early sowing: Later planting can delay plant growth until after the initial warm and damp period of early winter that favours wheat powdery mildew. This is important as infection of young plants can lead to increased losses at maturity.
For fungicide management tips and other information on wheat powdery mildew, read more here: 5542-AFREN-Wheat-Powdery-Mildew-Fact-Sheet_FA_online.pdf
