Phytophthora is a group of microscopic soil-borne pathogens that can cause dieback and root rot in a range of different plants. Different species of Phytophthora can cause dieback and root rot in different plants. While most species of Phytophthora affect a limited number of plants, Phytophthora cinnamomi can affect a broad range of plant species.

Phytophthora are not visible to the human eye and don’t always cause symptoms. A plant may appear healthy for a long time and suddenly exhibit symptoms when conditions change, for example after an increase in humidity. This means that it can be challenging to know whether the pathogen is present or not.

There is debate in scientific circles as to the date of its arrival in Australia. The mainstream view is that the devastation caused to the jarrah forests in Western Australia and the heathlands along the east coast, particularly the grass-trees (Xanthorrhoea) and proteaceous species, points to a post-1788 introduction.

Is Phytophthora cinnamomi present on the Island?

Two snippets of evidence suggest “Yes”. A study in the 1970s reported finding the organism (Benson 1980), but the results cannot be confirmed.

A multidisciplinary plant health survey in 2012-14 covered introduced plants, invertebrate pests of plants and animals, plant pathogens, pests and diseases of bees and diseases and parasites of domestic animals. In total, 1747 species were recorded across all organism groups. Phytophthora cinnamomi was not specifically targeted, but a sample collected to test for another pathogen was found to contain Phytophthora, though it was not identified to species level at the time. The sample was re-examined in 2019 and identified as Phytophthora cinnamomi.

The two records were not considered to be sufficiently strong evidence on their own to make a determination on the status of this pest. For this reason, Australian Government scientists visited the Island in February/March 2021 to collect more samples.The survey team collected 67 samples and processed them on Island before sending to Sydney for diagnostics.

Plant pathologist Harshitsinh Vala germinates seed of lupin (very sensitive to P.c.) to aid in detection.

Scientists Elizabeth McCrudden and Sandy Perkins take soil samples.

The visiting scientists advised that “The success of this survey would not have been possible without the support and guidance from the Norfolk Island Biosecurity staff and the Norfolk Island community, who have allowed the team generous access to homes and properties to collect samples.”

Importation of aggregate

Importation of aggregate for the Norfolk Island Airport Pavement Repair and Resurfacing project raised some questions about the status of Phytophthora on the Island. It was decided to treat Norfolk Island as if it were free from P. cinnamomi when imposing conditions for the aggregate importation. This decision was made to afford the Island the highest level of biosecurity protection possible until more complete information could be obtained. The 2021 survey of samples collected on a grid across the Island is intended to fill the gaps in knowledge.