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.
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.