REPORTS of stem rust in the Kondinin, Karlgarin and Hyden districts have prompted warnings from the Department of Agriculture and Food (DAFWA).
Rust pressure can result in losses of up to 90 per cent on susceptible varieties so authorities are taking the breakouts very seriously and asking growers to keep their eyes peeled and report any sightings.
According to DAFWA plant pathologist Kith Jayasena, stem rust has been found at low levels in a Halberd wheat hay crop growing near Varley and early-sown Yitpi crops may be at risk.
Dr Jayasena said early-sown varieties that are known to be susceptible to either of these rusts will need closest attention.
"The timing of fungicide application is important as early application at first rust detection in susceptible varieties will provide the greatest yield benefit," he said.
DAFWA plant pathologist Geoff Thomas said susceptible crop varieties made up more than 10pc of WA wheat crops and the incidence, particularly of stem rust, at this time of the year, was concerning.
"Stem rust is more common during warmer parts of the year," Mr Thomas said.
"It's considered more of a spring disease that arises towards the last third of a crop's life.
"Both stripe and leaf rusts require moisture for spores to infect leaves - a stripe or leaf rust epidemic is more likely if the winter and/or spring is suitably wet."
He said that leaf rust had a warmer mean daily temperature optimum than stripe rust.
"The mild winters in WA result in leaf rust being relatively active in winter and into spring, particularly in the northern agricultural areas," Mr Thomas said.
Dr Jayasena said previous trials held by DAFWA in the Esperance district indicated that stem rust could reduce yields in susceptible and partially susceptible varieties by 10 per cent to 53pc.
"If any stem rust is detected before head emergence, growers are advised to spray crops as soon as possible with an appropriate fungicide, at a high rate," he said.
"For crops with intermediate resistance, continue to monitor and spray if infection exceeds an average of five per cent of random stems infected."
Mr Thomas said best results were achieved when fungicide was applied at the start of a crop cycle rather than mid-way through.
"But if a grower does find it closer to harvest they still do need to look at spraying," he said.
"They just need to consider whether it would have an impact or not."
DAFWA has urged growers to inspect the most susceptible and earliest-sown crops carefully.
Mr Thomas said the key was to examine leaves at the top and bottom of the canopy for scattered light infections, and in green bridge areas also look for infrequent heavily-infected hot spots.
"Crops prone to infection at young stages should be inspected at seven to 10 day intervals from early stem elongation," he said.