SARDI scientists have confirmed severe outbreaks of a new more virulent form of the fungal disease on the popular variety, Keel, a feed barley, previously rated moderately resistant to the disease.

SARDI plant pathologist, Hugh Wallwork, says the net form of net blotch can be highly damaging - unlike the spot form.

"Initially only barley crops sown into infected barley stubbles were infected, but now airborne spores are spreading infection to barley crops over a wide area," Dr Wallwork said.

"Almost all barley varieties are susceptible at the seedling stage, but most will develop resistance as they mature.

"Growers will need to monitor crops closely and may need to apply fungicides – we strongly recommend they consult their advisors about options available.

"It is unusual to see heavy infestations of the net form of net blotch emerging so early in the season, so a vigilant approach is needed."

Dr Wallwork said the limited information available on controlling the net form of net blotch suggested that propiconazole and epoxyconazole (Opus) are likely to be the most useful fungicides, although azoxystrobin (Amistar Xtra) will also offer some protection.

"Fungicides will help protect crops for only two to three weeks, with crops being reinfected by airborne spores blowing in from infected crops," he said.

"For this reason, sprays are not likely to be economical if applied before growth stage 31.

"We are moving quickly to establish the ability of barley varieties and breeding lines to resist this more virulent form, so we have a good idea of sowing options available for next season and for replacement varieties."

Dr Wallwork's team are conducting glasshouse tests with a range of different fungal strains to understand more about the disease biology.

Also SARDI's pathology and crop evaluation teams have joined forces with private consultants to run spray trials to investigate the effectiveness and timing of fungicide applications.

"The outbreak of the net form of net blotch this year can be put down to three main factors: the increased practice of sowing barley into barley stubbles, the warmer than usual winter temperatures and the appearance of new virulence in the pathogen population," he said.

"Sowing barley into barley stubbles will also increase the chances that further changes in the net blotch population may occur in future.

"Looking ahead, growers should sow resistant varieties, avoid sowing barley into barley stubbles and remove volunteer cereals."

* Information available on SARDI’s website www.sardi.sa.gov.au - type 'net blotch' into the search field. A Crop Watch newsletter providing timely information on diseases in South Australian grain crops is available by sending an email to Jon Lamb Communications at jlcom@chariot.net.au