Biosecurity alert: Dickeya dianthicola

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.

The bacteria was detected in Australia, for the first time, in June 2017 on a Western Australian commercial potato growing property. In addition to seed potatoes, the bacteria has since been found in dahlia tubers and freesia bulbs imported from Victoria.

All potato, vegetable and flower growers, and production nurseries need to be vigilant and report suspect signs to the Plant Pest Hotline on 1800 084 881.

Current situation

The Department of Primary Industries and Regional Development (DPIRD), in conjunction with the Western Australian potato industry, will implement a management strategy for Dickeya dianthicola following a national decision that it cannot be eradicated.

The National Management Group (NMG) decision that the pest is not technically feasible to eradicate is based on the recommendation provided by the Consultative Committee on Emergency Plant Pests.

Quarantine restrictions on five commercial properties in WA have been lifted.

Further tracing activities are being undertaken by Victoria, New South Wales, South Australia and WA, including testing of available potato tubers, dahlia tubers in Victoria and WA, and freesia bulbs from Victoria.

The Potato Growers Association of WA (PGAWA) will lead management efforts to minimise industry impacts. This will include raising grower awareness of buyer responsibility to understand the risks of spread.

DPIRD will provide technical advice, fee for service laboratory testing and will work with PGAWA to modify the Certified Seed Scheme and Registration Rules to manage the disease.

There are currently no additional interstate trade restrictions being considered for potatoes apart from those restrictions in place for the tomato potato psyllid.

The international market access for WA potatoes remains unaffected.

Trade in cut flowers from WA is already subject to interstate movement conditions for other pests.

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

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.

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’

Farm biosecurity is essential

Dickeya dianthicola has a large potential host range and can persist in the soil for many months. In WA it has moved from dahlia to potato, proving that it can easily transfer between different crops.

A number of hosts may be asymptomatic. Therefore we strongly urge all growers to put in place, or maintain, strict on-farm biosecurity measures. This will help to restrict the spread and impact of this bacteria.

Biosecurity information sheets for Dickeya dianthicola can be downloaded from this website.

You can also get helpful information on the farmbiosecurity.com.au website. Some of the critical measures you can take are:

  • clean equipment, vehicles, machinery and footwear before entering a new crop, paddock, or another property
  • keep unnecessary visitors and vehicles out of your cropping paddocks
  • source your seed and bulbs from reputable suppliers
  • keep accurate records of seeds and plant material coming onto, and leaving your property.

​All potato, vegetable and flower growers as well as production nurseries need to be vigilant for signs of this pest in their crops. If you think your plants may be affected call the Exotic Plant Pest Hotline on 1800 084 881. 

Early reporting is critical in containing the bacterium and can lower the risk of it spreading to more properties. 

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).

How does it 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.

Management options

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: Wednesday, 25 October 2017 - 1:20pm