SARDI senior plant pathologist Dr Hugh Wallwork said the rust had probably blown in from northern New South Wales and therefore its presence in SA was unlikely to be confined to this region.
“Stripe rust likes cool temperatures and moist conditions, and is likely to spread rapidly, particularly if the weather warms up slightly, as it has done over the past week or so,” Dr Wallwork said.
“It is therefore strongly recommended that crops, particularly susceptible varieties, be monitored closely throughout the State.”
According to Dr Wallwork, it is not yet known for certain which pathotype (strain) is present in South Australia but Marombi, a dual purpose grain/grazing winter wheat variety mainly targeted for the NSW slopes, has the Yr17 (VPM) resistance gene, suggesting that the WA Yr17 pathotype of rust is present at Roseworthy.
“This is different from last season when the WA pathotype without Yr17 virulence predominated. Also, 19 out of 67 samples received from NSW and Queensland in Sydney before last week came from varieties carrying the Yr17 resistance.
“The only confirmed identifications of samples in Sydney have been the ‘Jackie’ strain which shows virulence on a range of triticale varieties including Jackie. Both strains may therefore be present in SA. Tests are underway on samples from Balaklava.”
Dr Wallwork said this season’s outbreak was later than last year’s but still early enough to cause significant damage to susceptible varieties. Spraying is recommended for these varieties where infection is observed in the crop or in nearby paddocks.
Spraying is also recommended in crops of varieties rated MR-MS or MS that are still at early growth stages.
More advanced crops of MR-MS or MS varieties are likely to be reasonably protected by partial adult plant resistance and spraying may be of less benefit in such situations.
“Growers should seek local recommendations for fungicide options,” Dr Wallwork advised.
Elsewhere in the State, severe leaf rust have been observed in a barley crop south of Maitland.
“The crop of Keel was sown early into a paddock with the alternate host Star of Bethlehem which was also carrying the rust and which would have been the source of infection for the barley,” Dr Wallwork said.
“The Star of Bethlehem, a white bulbous weed, can take infection from the black teliospores of leaf rust produced on barley straw and this provides a means for the rust to survive from one season to the next without requiring a green bridge. No similar alternate host of rust teliospores is known for wheat stripe rust. The barberry bush is an alternate teliospore host for wheat stem rust but is not endemic in Australia.”
Very low levels of leaf rust have also been spotted in scattered crops from Kadina to Curramulka on Yorke Peninsula.
Dr Wallwork said oat rust, which had been very quiet over the past two seasons, had been detected in hot spots in a crop between Streaky Bay and Wirrulla.
“It is not certain whether this is stem or leaf rust at this stage but leaf rust has been observed on wild oats around Lock.”