Alert on for surprise new powdery mildew
GroundCover™ Issue: 115 | Author: Elisabeth Berry and Tom Dixon
A new virulence of powdery mildew in barley has been discovered by researchers in trial plots in Narrabri, New South Wales. As a consequence, growers are urged to be cautious when choosing their varieties for planting this year
A new virulence of powdery mildew has been discovered by researchers in trial plots in Narrabri, New South Wales. Although powdery mildew is a controllable disease, this season northern barley growers are being advised to select varieties for planting with this potentially dangerous virulence in mind.
“Some of the more traditional varieties of barley, such as Hindmarsh, which were considered moderately resistant to the disease, could be quite susceptible to this new virulence,” says Queensland Department of Agriculture, Forestry and Fisheries (DAFF) senior researcher Greg Platz. He says tests show that Hindmarsh has recently become quite susceptible in Queensland.
The GRDC is funding research into the virulence to understand how it works and to help ensure growers are on the front foot with any outbreaks that could occur if weather conditions favour the disease this year.
Barley powdery mildew is a fungal disease that survives between seasons on stubble and plant residue. Infection appears as white fluffy patches on the leaf surface, producing windborne spores that spread the disease during the growing season.
Surviving over summer on stubble, the fungus again releases spores in the cooler, wetter conditions of autumn and winter, and these infect the new crop. Cases of high disease levels have been known to reduce yields by up to 15 per cent.
A persistent, yet fickle, pathogen, powdery mildew prefers humid conditions in the cool-to-mild temperature range, so it tends to diminish as crops mature and temperatures rise.
Queensland DAFF researcher Ryan Fowler says hotter conditions in the northern grains region generally do not favour powdery mildew due to the dry seasonal finish.
“We might get mildew early, but the pathogen dies off as it gets drier.
“Like some of the net blotches and rust diseases, mildew needs wet cycles to keep the disease running. Having had a particularly dry season this year, it wasn’t favourable for mildew,” Mr Fowler says.
However, following the discovery of a new virulence in trial plots at Narrabri, barley growers are advised to remain vigilant at planting this season.
Signs of susceptibility
The gene responsible for susceptibility to this virulence is called ‘MILa’, and it is present in several important, high-yielding malting and feed barley varieties, and food varieties such as Hindmarsh, which is now grown widely across Australia.
“Although we conducted an extensive survey in 2009–10, we didn’t detect this particular virulence then, so we think our discovery in 2014 is the first recording of it in Australia,” Mr Platz says.
“If growers are planting varieties that carry the susceptible variant of the MILa gene, those varieties are not likely to be as resistant as we once thought they were,” he says.
A quick response will be required if signs of powdery mildew are detected in these varieties, as populations of the pathogen can increase rapidly under the right conditions.
“If those humid and cool-to-mild conditions exist, and barley varieties carrying this gene are planted widely, mildew could expand right across the cropping region.
“Growers must be prepared,” Mr Platz says.
This winter-cereal-growing season, researchers will be observing the new virulence, tracking its dispersal and identifying whether it has spread further afield.
Preparing for outbreaks
“Although we’re still in the data processing stage, right now we are just warning growers, advising them to be aware that there’s a new virulence out there, that is likely to cause a problem in certain varieties,” Mr Platz says.
Researchers suggest early intervention, as well as an integrated crop management approach, is the most effective way to deal with a potential outbreak.
“It’s a matter of keeping up your crop surveys, making sure you’re on top of your disease pressures and managing your crop effectively,” Mr Fowler says.
Powdery mildew can be reasonably well controlled and there are several effective fungicides available. Growers can also use a seed treatment, or simply be prepared to monitor crops closely and keep up-to-date with varietal resistance ratings, as these can change from season to season.
Mr Platz says that while powdery mildew does not have a big effect on yield in the northern grains region, it is still worthwhile keeping on top of it with fungicides. “The economics would justify that,” he says.
Growers concerned about powdery mildew on their properties are urged to contact their local agronomist for advice.
More information:Greg Platz, Queensland DAFF, Hermitage Research Station, Warwick,
07 4660 3633, 0408 733 055,
GRDC Project Code DAQ00187