In selectively logged eucalypt forests in the central highlands of Victoria, it has been estimated that about 3-5% of the forest area is moderately to severely affected by Armillaria root rot caused by A. luteobubalina. A review of eucalypt plantations planted in New South Wales from 1994 to 2005 found that infection by A. luteobubalina was rare, and only accounted for 1% of mortality in total. In this instance, the cases had been restricted to Eucalyptus nitens on the Dorrigo Plateau. Unlike other Armillaria species found in Australia's native forests, which require a host tree to become weakened by prior infection by a different species, A. luteobubalina is a primary pathogen, and can infect healthy trees. Tree roots may be infected for years before showing above-ground symptoms, making it difficult to accurately assess the true extent of disease in a forest stand. Surveys are usually conducted in autumn, to coincide with the appearance of fruit bodies; infection is assessed by the presence of basal scars on the trees, and the appearance of fruit bodies. Several factors, however—such as cost, variable on-site conditions, and non-symptomatic diseased trees—make it difficult for such surveys to reliably detect all infections. One study showed that above-ground examinations detected only 50% of the trees actually infected, leading to underestimation of the incidence of true infection by 20-40%. The study used more intensive surveying methods to determine that 25- to 30-year-old karri regrowth forests in western Australia showed an average of 40-45% incidence of infection.