Biosecurity alert: Dickeya dianthicola

The Western Australian Department of Primary Industries and Regional Development has confirmed the detection of Dickeya dianthicola in seed potatoes and dormant dahlia tubers in Western Australia, and is responding with measures to contain the pest, determine spread and assess the feasibility of eradication.

Dickeya dianthicola is a serious bacterium that can cause tuber soft rot and blackleg in potatoes, and can also affect some ornamental varieties, chicory and artichoke.

Growers of these crops are urged to check plants and tubers, and report any suspect symptoms.

Grower information sessions

The Potato Growers Association of WA and the Department of Primary Industries and Regional Development (DPIRD) will be holding three grower information sessions over the coming weeks

  • Friday 25 August - Manjimup* 11am-1pm DPIRD office, 28527 South West Highway (Tel: 9777 0000)
  • Tuesday 29 August - Bunbury* 10am-12pm DPIRD office, Verschuer Place (Tel: 9780 6100)
  • Thursday 31 August - Gingin* 10am-12pm Gingin Recreation Centre, New Street

    (in front of the Gingin Aquatic Centre) (Simon Moltoni Mob: 0447 141 752)

*Lunch included. Please advise of any dietary requirements.

RSVP required - email pdd-IMTsupport@dpird.wa.gov.au or call Julie Mercer on 9368 3739.

What is Dickeya dianthicola 

Dickeya dianthicola causes soft rot and blackleg in potatoes. It is a serious pest (bacterium) that was not previously known to occur in Australia. Overseas data has indicated significant yield losses in potato crops.

Dickeya dianthicola can also infect other crops, including some ornamentals (including carnation, lily, chrysanthemum, dahlia, begonia, flaming Katy, freesia, hyacinth and iris), globe arichoke and chicory.

Other pathogens already present in Australia can cause similar soft rot and blackleg symptoms. However, Dickeya dianthicola is more aggressive and causes disease at lower infection levels.

This pest is not associated with the tomato potato psyllid.

Department of Primary Industries and Regional Development (DPIRD) response

The pest has been confirmed on four commercial potato growing properties. Five properties have been placed under quarantine. The quarantine notices stipulate movement restrictions on host plant material, soil and machinery.

DPIRD is continuing to trace the movement of potatoes and dahlia tubers to and from infected properties and to collect samples from the highest risk properties, in order to determine the extent of the outbreak as soon as possible.

DPIRD is working closely with the WA industry and national stakeholders to minimise the impact of this new pest. The Consultative Committee on Emergency Plant Pests (CCEPP) has met to discuss this detection. The committee has kept open the possibility for eradication, dependent upon further surveillance.

This particular pest is not associated with the tomato potato psyllid that was detected in Western Australia earlier this year.

The bacterium does not have an impact on human health.

Host list

  • Potatoes
  • Globe artichoke
  • Chicory
  • Begonia
  • Calla lily
  • Carnation
  • Chrysanthemum
  • Dahlia
  • Dianthus, Sweet William
  • Freesia
  • Hyacinth
  • Iris
  • Kalanchoe, ‘Flaming Katy’ which is also known as ‘Christmas kalanchoe’, ‘florist kalanchoe’ and ‘Madagascar widow’s thrill’

Trade impacts

Trade in potatoes from WA is currently prohibited due to the tomato potato psyllid outbreak, and interstate movement controls for risk material continue to apply. In response to TPP, WA is working with other state and territory governments to develop protocols to support future interstate movements of risk material.

Trade in cut flowers from WA is already subject to interstate movement conditions for other pests. At present there are no further trade restrictions in relation to Dickeya dianthicola.

The Australian Government Department of Agriculture and Water Resources will work with overseas trading partners should any issues arise.

Helping growers to maintain normal business operations

DPIRD recognises this detection comes at a difficult time for the horticulture industry, in particular potato growers, following the detection of the tomato potato psyllid earlier this year.

If issued with a Quarantine Notice, Pest Control Notice or Direction Notice under the Biosecurity and Agriculture Management Act 2007 (the BAM Act), growers cannot move or sell infected plants/tubers from properties without written approval from a DPIRD inspector, who are authorised under the BAM Act.

DPIRD is working with affected potato growers to provide approvals that can help resume their business, while at the same time making sure the pest does not spread any further. To achieve this, DPIRD is carrying out risk assessments of operations, and helping growers to develop a plan for the movement and sale of their ware potatoes.

Each property is being assessed on a case by case basis.

See the attached fact sheet - Quarantine and your business - for more information on positive samples and Notices.

Potatoes

Symptoms

The first symptom of the disease can be poor emergence due to rotting seed tubers. Plants wilt and typically have slimy, wet, black stems extending upwards from the rotting tuber. 

Infected tubers are macerated and have a tapioca-like appearance, but may not have the pungent smell associated with typical blackleg.

According to overseas data, Dickeya dianthicola can also cause soft rot and wilting in ornamental crops.

Dickeya dianthicola can be present in a plant without causing symptoms, particularly if temperatures remain low. Symptoms often develop after a period of hot weather, especially when plants are also stressed. 

See the attached fact sheet for more information.

How does it spread?

In potatoes, it is generally accepted the main source for blackleg infection is latently infected seed tubers.

Overseas data indicates that as infected tubers rot, the bacterium is released into the soil. It can then be transmitted through water in the soil and contaminates neighbouring tubers, and infected stems can also affect neighbouring plants through contaminated irrigation water.

Additionally, infection has been shown to spread to other tubers during storage. Overseas research indicates that Dickeya dianthicola does not survive long in soil without a host. Although bacteria can survive between potato crops in soil when there is remaining plant debris or when volunteer potatoes are present.

Management options

Generalised management techniques developed for soft rot diseases in potatoes may be useful for growers affected by Dickeya dianthicola. Refer to the soft rot web pages for further information.

Additionally, on-farm biosecurity practices, such as good farm hygiene and early reporting of suspicious symptoms should be in place to prevent the entry, establishment and spread of pests and diseases.

Practical advice and information to assist is available through the Farm Biosecurity website.

Additionally, a farm biosecurity checklist can be downloaded from this page.

Dahlias

Dickeya dianthicola has been causing losses in dahlia crops overseas for many years. The information below has been sourced from recent research at the University of Wageningen in Holland.

Symptoms in dahlia tubers and plants

  • Poor emergence.
  • Plant growth may be restricted.
  • Weight of tubers produced can be reduced by up to 56%.  
  • Stems of infected dahlia plants are darker green than healthy plants.  
  • Hot and dry conditions cause wilting of infected plants.  
  • If conditions are perfect for plant growth, plants may not show overt disease symptoms, but will produce infected daughter tubers.  
  • Even large, healthy-looking tubers may be infected.
  • Infected tubers may rot, especially when wet.
  • Experiments show that some dahlia varieties are much more susceptible to Dickeya than others, ranging from 9%-56% crop loss depending on variety (although variety names that were tested were not available).

Pathways for spread

  • Dickeya is readily transferred from infected plants to healthy plants on blades used for cutting the tops of dahlias, and the disease spreads after soil cultivation.
  • Overhead irrigation can spread the disease, especially after flowers are cut or if foliage is damaged.
  • If healthy planting material was used, disease was minimal.

How to prevent spread

To minimise the impact of Dickeya dianthicola in dahlias:

  • Use healthy planting material. Do not plant any tubers showing signs of rotting.
  • Ensure all blades and equipment used on dahlias are sterilised frequently.
  • Ensure gloves are clean.
  • Consider using drip irrigation rather than overhead watering.
  • Maintain clean work and storage areas.
  • Ensure good ventilation when dahlia tubers are stored. Mesh bags or bins can assist with this.
  • Avoid mechanical damage to tubers and plants as wounds can provide a route for bacteria to enter the plant.

Practical advice and information to assist is available through the Farm Biosecurity website.

Additionally, a farm biosecurity checklist can be downloaded from this page.

Reporting options

Dickeya dianthicola (Samson et al. 2005) is a prohibited organism for Western Australia. It is important any suspect disease occurrences are reported.

Growers can report any unusual plant symptoms by:

  • Calling the Pest and Disease Information Service on 1800 084 881, or
  • Sending a photo to DPIRD via the MyPestGuide Reporter app available from the Google Play or Apple store, or
  • Emailing photos with your name, address and mobile number to info@agric.wa.gov.au

 

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080
Page last updated: Tuesday, 5 September 2017 - 12:57pm