TESTS on the strain of stripe rust now established in the state's wheatbelt have revealed that it originated from overseas.
Agriculture Department cereal pathologist Robert Loughman said samples were tested at the University of Sydney to determine whether the fungus present in WA was from interstate or overseas.
"Initial genetic tests at the University of Sydney's Plant Breeding Institute showed several characteristics of the stripe rust in WA were distinctly different from other pathotypes or strains that occur in eastern Australia," Dr Loughman said.
Dr Colin Wellings, with the Australian Cereal Rust Control Program at Sydney University, said the WA rust was able to attack Stiletto, Westonia and Camm wheats, each of which have different stripe rust resistance genes.
"This combination of virulences has not been found in Australia before," Dr Wellings said.
When stripe rust was first detected in eastern Australia in 1979, genetic tests found it was similar to strains of the rust common in Europe at the time.
"From the current outbreak in WA, it is likely the disease was introduced inadvertently from overseas as happened in eastern Australia 23 years ago," Dr Wellings said.
Rust spores are microscopic and have been known to travel very long distances within regions and between continents, given the right atmospheric conditions.
Dr Loughman said for example, wind movement of rust from southern Africa was believed responsible for some past outbreaks of stem rust in Western Australia.
He said the present outbreak of stripe rust in WA could have resulted from natural long distance wind transport of spores or through accidental introduction by a visitor from other contaminated farming areas.
Stripe rust continues to spread and has now been found in the Esperance region. Good control with fungicide is being reported where the disease has been detected and treated at early stages of infection.
Dr Loughman said growers should check their crops for yellow-orange spore masses on leaves. The spore masses would be in long stripes.
"How we deal with this disease next year will be determined from variety performance being monitored in trials this year. This information will enable us to identify the best variety options for growers in the lead up to harvest," Dr Loughman said.
Suspected samples of stripe rust can be sent to the Department of Agriculture for free identification. Growers seeking confirmation of identification need to gather up to 20 leaves bearing signs of stripe rust and send them in a paper envelope with contact details and location numbers to AGWEST Plant Laboratories, Department of Agriculture, Locked Bag No. 4, Bentley Delivery Centre 6983.