New cereal rusts from overseas could cost Australian growers hundreds of millions of dollars.

On top of the cereal rust diseases already in Australia - which could cost grain growers hundreds of millions of dollars annually in lost production and chemical control - there is the continual threat of new cereal rusts from overseas.

Dr Lisle Snyman, senior plant pathologist with the Queensland Department of Agriculture and Fisheries, has highlighted some of these cereal rusts to colleagues at a workshop on exotic pest surveillance.

"The most well-known is Stem rust pathotype Ug99 (Puccinia graminis f.sp. tritici)," she says.

"Named after its first identification in Uganda in 1999, Ug99 has since spread to 13 countries.

"Ug99 and its mutants can overcome 17 of the 34 known rust resistance genes and it is estimated that 28 per cent of currently grown wheat varieties are moderately susceptible to the disease."

Huge potential cost of Ug99

In 2018, an Australian Bureau of Agricultural and Resource Economics (ABARE) report estimated that an outbreak of Ug99 would cost Australia up to $1.4 billion over 10 years. Costs would include:

• lost production and quality;
• chemical control; and
• the opportunity costs of refocusing breeding efforts to deploy new resistance genes.

"Another threat is Digalu race, a lesser-known but potentially just as devastating Stem rust pathotype first identified in Turkey in 2005," Dr Snyman says.

"Since then, it has spread to nine countries - most recently Kenya in 2016. There are also variants of this rust race in Germany and Denmark.

"Like Ug99, many current Australian commercial wheat varieties would be susceptible to Digalu race and it would cause significant loss if established in the cropping regions."

Another rust threat to cereal production Dr Snyman described is barley Stripe rust (Puccinia stiiformis f. sp. Hordei), which is considered the most important disease of barley in the western US - where more than 69 races have been identified.

"It is widespread in the United States, Asia, Africa, Europe, the United Kingdom, the Netherlands, Columbia, south America and Mexico, but so far Australia has been able to avoid an infestation," Dr Snyman says.

If rusts from overseas, such as Ug99, Digalu race or barley Stripe rust were to enter Australia, eradication or long-term containment are unlikely.

However, if they are detected early, it may be possible to slow their spread, implement improved management practices and deploy new genetic resistances to reduce the impact of the diseases.

What you can do:

• Look out for unusual rust infections, for example a yellow Stripe rust on barley or Stem rust in a resistant wheat variety.
• Report anything unusual to the Exotic Plant Pest Hotline (1800 084 881) or your local pathologist.
• Come and go clean when travelling overseas. Ensure your clothing and footwear is clean before returning, especially if you have been inspecting crops in other countries. Studies show that rust spores on clothing can remain able to infect a crop for up to seven days and investigations of past rust incursions indicate that they have been carried via people, probably on clothing.
• Eliminate your green bridge. Good crop hygiene includes making your best effort to clean up any volunteer cereal plants from your fallow for at least one month before planting a cereal crop. This reduces the build-up of inoculum for the cropping season.