The disease, which has been present in south-eastern Australia for many years, can cause yield and quality impacts in oaten hay and grain crops.

Department of Primary Industries and Regional Development (DPIRD) officers detected the disease in samples collected from Narrogin, Piesseville and Pingelly, WA, as part of general crop surveillance.

DPIRD research scientist Geoff Thomas said given the geographic spread, it was likely the disease had been present from more than one season.

"RLL, caused by the fungus Neospermospora avenae, can reduce hay and grain yield and quality and significantly impact hay appearance and colour," he said.

"We will be surveying oat crops for this disease, and we are giving growers the opportunity to submit any suspect samples to DPIRD for testing.

"Symptoms include distinct lesions on leaves featuring a lighter centre with dark margin which over time join together and eventually become read and leathering in appearance.

Thomas said it could easily be confused with bacterial stripe blight and even with Septoria.

"The disease often becomes visible on lower leaves at the tillering stage and much like other stubble borne diseases, progresses up the crop canopy during the season driven by cool, wet weather," he said.

"Continuous oat crops in cooler, higher rainfall environments are at greatest risk," Thomas said.

There are no fungicides currently registered for RLL in oats, however fungicides registered in oats for other foliar diseases have been shown to reduce disease severity in eastern Australia.

For more information about RLL and other oat diseases, visit https://www.agric.wa.gov.au/oats