Bacterial canker of kiwifruit

Bacterial canker of kiwifruit is caused by the bacteria Pseudomonas syringae pv. actinidiae (PSA).

There are different strains of PSA. Some are mild (like those detected in Victoria in 2011) and others are more aggressive. The effects of PSA depend on the:

• strain type
• vine cultivar
• weather conditions.

Symptoms of PSA

The early signs of PSA are dark spots on leaves of vines – but these may not always be present.

As the disease progresses, symptoms include:

• brown discoloration of buds
• dark brown spots surrounded by yellow haloes on leaves (Figure 1)
• cankers with reddish exudate on twigs, leaders and trunks (Figure 2)
• collapse of fruits.

Infected plants can eventually die.

Spread of disease

Over short distances PSA can be spread by:

• heavy rainfall
• strong winds
• mechanical transmission such as grafting
• animals.

Over long distances, PSA is spread by nursery stock. The PSA bacteria has also been found on pollen, but it's unclear whether pollen can cause infection.

Laboratory tests have been unable to infect fruit – fruit is not considered to be a way for PSA to be introduced or establish.

PSA can also affect weeds

PSA is also known to infect:

• Alternanthera philoxeroides (alligator weed)
• Paulownia tomentosa (paulownia)
• Setaria viridis (green foxtail)

All growers should practice good weed management to stop the spread of PSA.

Environmental conditions

Symptoms are likely to occur in wet and cool weather conditions. The bacteria can be present without symptoms in other conditions.

In other countries symptoms are usually expressed in spring and autumn when favourable conditions are present.

Where PSA is found

The disease is considered established in Victoria.

PSA disease is present in:

• Argentina
• Chile
• China
• France
• Italy
• Japan
• Korea
• New Zealand
• Portugal

Photo credits

All photos courtesy of Plant Protection Service of Emilia-Romagna region, EPPO