Month: June 2017
Pest of the month: Bacterial wilt (Ralstonia solanacearum)
Category name: Bacteria
Importance: Emergency disease: No, however not found in Western Australia.
Symptoms: The bacterium that causes bacterial wilt is a xylem vessel coloniser which produces cell wall degrading enzymes. The pathogen multiplies rapidly in the vascular tissue and fills xylem with bacterial cells and slime, thus preventing water uptake. This vascular occlusion causes browning of vascular tissue and chlorosis, stunting and wilting of plants. Adventitious roots may form in the stem. Tubers, corms and large roots of infected plants are often decayed. When an infected stem is cut crosswise and placed in water, a white bacterial ooze streams from the cut stem.
Transmission: As latent infections especially in vegetative planting material (e.g. seed potato) or seedlings. Massive populations of bacteria are released from diseased plant tissue into soil and watercourses favouring transmission by irrigation and surface water; soil adhering to farm or nursery implements; root contact (plant to plant spread). There is also insect transmission (e.g. Moko disease of banana).
Favoured by: Wounding of roots during transplanting and cultivation, by nematodes and soil insects, which facilitates pathogen entry. Applying excessive amounts of nitrogenous fertilizer or animal manures. Rotation with susceptible crops and failure to control alternative weed hosts and volunteer plants. Most strains of the pathogen are favoured by warm temperatures; the potato strain prefers cooler temperatures.
Host range: More than 35 genera in 50 plant families. Important hosts include tomato, potato, eggplant, capsicum, ginger, dahlia, Heliconia, Strelitzia, zinnia, custard apple, banana, Eucalyptus, peanut.
Further industry pest information is available at www.pestid.com.au
An initiative of the National Nursery Industry Biosecurity Program (NY15004) and the ‘Building the resilience and on-farm biosecurity capacity of the Australian production nursery industry’ Project (NY15002).