Bacterial blast

Pseudomonas Syringae
Also known as Canker, Bacterial Canker or Gummios.

Bacterial blast is a disease that presents itself by creating open cankers that ooze an amber coloured gum on branches or trunks of trees. The oozing gum contains the bacteria so is a source of the spread.

Other symptoms include the dieback of branches and growth tips, flower blossoms turning brown and clinging to the tree, leaves may have dark brown spots that drop out.

Stone fruit trees can leak sap which has no smell and is quite normal, if it smells like sweet golden syrup then it is likely to be Bacteria Blast. A sour odour like fermenting beer can come form the trunk or branches and is referred to as Sour Sap, this occurs under the bark in areas that are infected.

Bacterial blast lives on plant surfaces and is spread by splashing water, usually occurring from rainfall or over head watering. This disease grows in periods of damp and wet conditions with low temperatures, and in Auckland it usually presents itself in spring.

Minor infections in branches can be controlled by hard pruning, but major trunk infections will often kill a tree.


If caught early, bacterial blast can be managed.

Spring is when symptoms of the disease are more obvious which can show on any part of the tree.

If you are pruning plants over winter, always make sure you wait for dry weather. If the pruning cut you make is larger than 1cm, immediately apply Grosafe Organic Prune N Paste to help prevent infection.

Equipment hygiene is important as tools that have infected sap on them can spread the disease. Clean tools in between pruning each tree with methylated spirits.

Implementing a regular spray program is essential to protect against diseases. Grosafe Free Flo Copper Spray with at leaf drop, and then every 4 weeks until bud movement then treat as per leaf curl.

Certain rootstocks have been known to have better resistance to bacterial canker. Always choose a fruit tree from a garden centre, as stone fruit trees grown from seed are more likely to contract diseases.


If the infection is minor on outer limbs, cut back the diseased wood and remove it from the property.  Prune to 10cm below obvious signs of the infection. Often the wood will have a brown stain to it, so prune back past this as this is a sign of infection.

Dispose of all infected clippings in the rubbish, do not compost or use as mulch as this can spread the disease.

After pruning spray infected plants with Grosafe Free Flo Copper

If the infection has spread to the trunk, you will need to dispose of the tree, as heavily infected plants cannot be treated.

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