Shadow agriculture minister John Cobb says the koala's habitat is under threat from myrtle rust, which infiltrated Australia in 2010, first in NSW and has since spread to far north Queensland. Last month, it was detected in Victoria for the first time.

''Myrtle rust will trigger the end for some of our iconic koala populations and hasten its inclusion in the endangered species list - yet the Gillard government doesn't care,'' Mr Cobb said.

He blamed the department and Agriculture Minister Joe Ludwig for failing to take the threat seriously, saying a $1.5 million allocation for the management of myrtle rust was yet to been spent. ''Due to Labor's ignorance and inaction, the latest casualty of the rampant disease is now the forest red gum, the major food source for koalas,'' he said.

The disease attacks tree leaves and is easily spread because it produces thousands of spores. Mr Cobb said it would bankrupt nurseries and commercial timber plantations if the problem continued unchecked.

An expert in koala habitat, Dr Mathew Crowther of the University of Sydney, said the disease would exacerbate the major cause of dwindling koala populations, habitat reduction. He said koalas were restricted in the trees they could eat because of the different levels of toxins in them.

''There can be a major issue with the quality as well. If myrtle rust gets in and affects the [leaf] quality it might not be worth the koala eating it, they won't get the energy.''

Koalas are not on the federal endangered list but in NSW they are listed as vulnerable and in south-east Queensland they are listed as threatened.

Environment Minister Tony Burke is considering whether to put the koala on the threatened list, following a Senate inquiry last year. He is due to make a decision by February 17.

Australian Koala Foundation chief executive Deborah Tabart said the group was aware of the myrtle rust threat and had had concerned calls from the public about the disease. ''I don't believe the government is taking it seriously. I have no doubt that it's affecting koala trees,'' she said.

A spokeswoman for Mr Ludwig said the funds had been allocated to projects that will position authorities and industry to effectively manage the impacts of myrtle rust into the future.