Stem rust has been found in an area of about 16 kilometres in diameter near Kalanbi, north-west of Ceduna. Crops of Yitpi have been mostly affected.
SARDI senior plant pathologist Dr Hugh Wallwork said that a single infected plant has also now been observed at Pt Kenny on the West Coast, suggesting that the rust has been distributed more widely.
“Most crops in the area are in advanced stages of grain filling so should escape severe damage,” Dr Wallwork said.
“Continuing humid weather will, however, encourage further infection and spread of rust, and any later sown crops will be vulnerable so paddocks of susceptible varieties should be closely monitored.”
Dr Wallwork said it was likely that the stem rust established in one or more crops which were sown in early April when conditions were warmer.
“Stem rust develops very slowly under colder winter conditions but the autumn infection will have allowed for rapid development of the epidemic with warmer spring temperatures.”
According to Dr Wallwork, leaf rust is now widespread in wheat crops on the West Coast of SA. Infected crops on the West Coast include the susceptible varieties Westonia, Excalibur and BT Schomburgk.
“Early sowing of such susceptible varieties in coastal areas is likely to make leaf rust a continuing problem so these older varieties should be replaced for 2010,” Dr Wallwork advised.
“This will also help to minimise the possibility of new rust mutations occurring.”
Leaf rust has also just been recorded in Yitpi wheat near Roseworthy. The good news is, according to Dr Wallwork, that most varieties in the Lower North are at least only moderately susceptible to leaf rust so the rust epidemic in that region should not build up too rapidly.
With all three wheat rusts being present in SA, growers should monitor crops for the presence of each rust and consider fungicide treatments where crops are still young enough to benefit. Further reports of leaf and stem rust would be gratefully received by Hugh Wallwork on (08) 8303 9382.
The Grains Research and Development Corporation (GRDC) has provided growers with a central resource for cereal rust management information at www.grdc.com.au/rustlinks.