Psa

Pseudomonas syringae pv. actinidiae (Psa) is a bacterium that can result in the death of kiwifruit vines. Psa carries no risks associated with human or animal health and does not affect plants other than kiwifruit vines.

Growth of the bacteria outside/inside the vines can result in leaf spotting, cane/leader dieback and, in extreme cases, vine death accompanied by the production of exudates (a rusty red liquid discharge).

Symptoms are usually expressed during spring and autumn when climatic conditions are favourable – i.e. cool temperatures, persistent rains and high humidity.  Psa is temperature sensitive and active between 10 to 20 degrees but limited by temperatures over 25 degrees. The disease can be spread via windborne pollen, strong winds and heavy rainfalls. It is also believed to be spread by footwear, vehicles and orchard tools, animals and humans. The bacterium infects the plant through natural openings (stomata and leaf axis) and wounds.

Symptoms include angular shaped spots, often associated with a halo, although not all leaf spots clearly exhibit the halo, brown discolouration of buds and, in advanced stages of infection, the leakage of red-rusty gum.  Not all symptoms appear at the same time