kiwifruit bacterial canker (PSA)

Symptoms

Brown-red leaf spots with yellow halos, dark bacterial ooze from stem + trunk cankers during spring sap flow (very diagnostic), dead flowers + flower buds, branch dieback + wilting, complete vine death within 1-3 years of infection, cankers re-open + sporulate every spring.

Easily confused with

• grey mould (Botrytis)

  How to tell them apart: On kiwifruit (Actinidia deliciosa), Botrytis cinerea (grey mould) ends as a soft, fuzzy grey-brown sporulating felt that smothers spent blossoms, mummified fruitlets and the cut edges of dead leaf tissue, and it spreads from collapsed flowers inward; leaf lesions stay irregular, tan and papery with no coloured ring. Pseudomonas syringae pv. actinidiae (PSA bacterial canker) instead makes small (2-3 mm) angular brown-to-red leaf spots ringed by a bright yellow chlorotic halo, and the giveaway sign is rust-red to white bacterial ooze weeping from cracked cankers on canes and the trunk during spring sap flow, with wilting cane dieback above. If you see fuzzy grey mould it is Botrytis; if you see haloed angular spots plus oozing stem cankers it is PSA.

• Phytophthora root + crown rot

  How to tell them apart: On kiwifruit, Pseudomonas syringae pv. actinidiae (PSA) attacks above ground: look for rusty red-brown leaf spots ringed by bright yellow halos, dead flower buds, and rust-coloured to milky-white bacterial ooze weeping from cracks in the trunk, leaders and canes — the ooze is heaviest in spring at sap flow and the cankers re-open and run every spring. Phytophthora cinnamomi instead works at or below the soil line: the canker is a dark, sunken, water-soaked patch at the very base of the trunk and crown, and when you peel the bark you find a sharp V-shaped chocolate-brown lesion, while the root system is rotted to slimy stubs with only a few white feeder roots left. Decisive tells: ooze + yellow-haloed leaf spots high in the canopy point to PSA; rotted roots + a soil-line V-lesion with no leaf spots point to Phytophthora.