ADAS plant pathologist Tim O'Neill said the disease, which can be carried either on the seed coat or in the seed embryo, is particularly infectious and difficult to control due to a shortage of effective chemicals.
Bacterial canker produces a range of symptoms, several of which can be mistaken for other diseases, but some are superficial, where the disease is not yet being carried in the plant's internal transport system, and others are systemic. Superficial symptoms are spread by water splash and include small irregular pale areas on foliage, white mealy pustules on one side of the stem and bird's eye spotting of fruit. Once the disease is systemic, either because the seed embryo was infected or where bacteria have entered the plant through pruning wounds or damaged roots, leaves develop pale "windows" and plants wilt and die.
"Seed is considered the main source but bacterial ooze, which has dried on structures or tools, is how the disease can survive," said O'Neill.
Propagation nurseries have a statutory duty to report an outbreak but there is no similar requirement for production nurseries, although O'Neill said it would be good practice to report an outbreak so that it was properly identified.
"An outbreak can be contained if the disease is detected early and there is no superficial infection," he said.