A nationally coordinated response to stop citrus canker has been underway since the disease was first detected in Darwin, Northern Territory in early April 2018.
In that time, a total of 15 citrus canker infected premises (IPs) have been identified with 12 in the north of the Northern Territory (NT) and 3 in northern Western Australia (WA), and these areas are the focus of eradication efforts. The NT and WA detections are being treated as a single incident due to the link back to a single source of disease at a Northern Territory production plant nursery.
The initial response strategy, agreed to by Emergency Plant Pest Response Deed (EPPRD) Parties, has involved implementing emergency containment activities and movement controls to reduce the risk of further spread of the disease, while defining the extent of the incursion through delimitating surveillance and tracing activities.
Operations to respond to the current known situation have focussed on tracing potentially infected plants, and inspection and removal of diseased plants.
A Restricted Area (RA) of a minimum 600 m is established around each IP and all citrus canker host plants are removed. A wider Control Area (CA) is established as a buffer zone around one or a number of RAs to control the movement of hosts into and out of the area while the response is underway.
Available evidence indicates that citrus canker is still restricted to potted plants in the home and garden sector, and that all infected premises are linked to the NT nursery. Ongoing surveillance continues to show no signs of the disease in commercial citrus orchards or urban plantings in any other Australian state or territory. There is also currently no evidence of spread from traced infected plants to other host plants on the IPs.
The Department of Agriculture and Water Resources (DAWR) has been investigating a number of credible potential entry pathways including legal import pathways, natural spread scenarios and potential illegal avenues and the risk of the disease occurring undetected at unidentified locations. While the origin remains undetermined, the most likely pathway is the illegal importation of infected plant material from an overseas source by an unidentified person.
Since early April 2018, the agencies and groups participating in the nationally coordinated response have:
- confirmed the presence of Xanthomonas citri sub sp citri (Xcc) through disease symptoms, molecular diagnostics and DNA sequencing in line with the national diagnostic protocol
- completed around 7,000 individual plant movements from the NT nursery, which have been investigated across Australia. No disease has been found outside the currently identified IPs. All Primary (direct contact) traces have been completed, and most secondary receipt sites have been identified. Only some tertiary premises have been identified, and many of these are unresolved due to a lack of traceable sales records from cash sales in the retail supply chain. These unresolved traces represent approximately 1500 plants which remain a significant focus of the ongoing response activities.
- surveyed 9,653 premises across NT and WA to September 2018. These include retail nurseries and outlets, residential properties, and production nurseries, with activities guided by public hotline enquiries and tracing data (table 1)
- confirmed 15 IPs; 10 in the Greater Darwin Rural Area (GDRA) NT, one in Katherine (NT) and one in Marrakai (NT), two in Kununurra (WA) and one in Wyndham (WA). This has required the establishment of one Control area in WA and two in NT
- removed thousands of host plants to 24 September 2018 (table 2)
- agreed and implemented interstate arrangements for the safe movement of fruit from the CAs
- agreed and implemented the cessation of movement of host plant material within the CA and interstate
- secured ongoing market access for Australian citrus to Europe, NZ and the USA
- handled 1,089 hotline calls, 32 online forms and 84 email enquiries from the public.
Table 1: Total premises surveyed NT & WA to September 2018
|Restricted Areas (total)||Control Areas (total)||Areas of Interest (NT only)||Rest of NT and WA|
Table 2: Host plants removed to 24 September 2018
|# Premises with host plants||# cleared of host plants||% Premises completed||# host plants||#host plants removed||% removed|
|Infected Premises and Restricted Areas||51||51||100%||1,520||1,520||100%|
Based on the propagation, consignment, tracing, sampling and diagnostic information collected to date, varying levels of risk associated with plant movements have been identified in several states as follows:
NSW and Qld: A total of some 2,500 at-risk plants were traced into NSW and Qld. The majority of these (over 2,200) were received by a north-east NSW production nursery as tube stock. During the growing out of these plants, no citrus canker was evident. This tube stock ultimately resulted in less than 1,000 plants being consigned to retail outlets in eastern NSW and Qld, of which 473 have been located, inspected and found free of canker. A further +/-30 advanced plants were also consigned to a retail outlet in Brisbane, of which 19 have been located and found free of canker. An additional +/-30 plants were consigned to a north-western Qld retail outlet. Ongoing surveillance in all of these receiving areas will be undertaken to address the very low levels of residual risk.
South Australia: Of the advanced plants distributed by the NSW production nursery, some 30 were consigned to an Adelaide retail outlet. 22 of these have been located and inspected, with no canker evident. Baseline surveillance will continue to address the very low residual risk in this area.
Western Australia: A total of 516 at-risk plants have been traced to WA. 140 of these have been located and addressed, leaving some 380 to be addressed through the ongoing response. Of the 516 consigned plants, 88 were Tahitian limes (which is the only variety found to be infected in WA). 46 of these 88 plants have been located and addressed, with 7 positive diagnoses among them. Based on infection detected to date and the plant numbers yet to be addressed, there is the potential for fewer than 10 infected plants remaining to be addressed through the ongoing response. Tracing and surveillance activity over the coming two years will address this residual risk.
Northern Territory: Consignment and tracing analysis has identified some 2,400 at-risk plants that have been distributed within NT. Of these, some 900 were removed from the 12 confirmed Infected Premises to which these plants were traced. The remaining +/-1,500 at-risk plants continue to be the focus of primary, secondary and tertiary tracing. At-risk plants continue to be located through this tracing and through community engagement activities. Area of interest surveillance, based on distribution of at-risk plants, will continue to address the remaining level of risk, in conjunction with community engagement and other response activities. Based on the level of infection evident to date, it is estimated that there are potentially 70-150 infected plants remaining in NT to be addressed by the ongoing response.
EPPRD parties, including Citrus Australia and NGIA, are currently revising the national response plan with the aim of successfully eradicating citrus canker from Australia and reinstating country freedom from the disease within three years.
The impact of the wet season on disease expression and spread is a key factor in the proposed timeframe for eradication and the response strategy will be assessed in July 2019 to confirm the ongoing technical feasibility of eradication after the 2018-19 wet season.
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More information on how we’re responding to the citrus canker incursion is also available on www.outbreak.gov.au