Cankers are serious diseases of woody plants and shrubs, caused by either fungal or bacterial pathogens. Canker refers to a symptom of an injury, often associated with an open wound that has become infected by a pathogen.

These pathogens invade wounded plant tissues – caused by either natural or mechanical means – and typically results in excessive gum exuding from entry sites (gummosis), wilting and death of branches, and eventual death. The severity of canker depends on the environment, the age of the plants, and if the plants are under any other stress – these factors can all reduce plant defence reactions. Here, we explore the most common canker diseases and how to control them.

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Image above: Bacterial Canker of cherry.

What is Bacterial Canker

Pseudomonas syringae pv. syringae

Bacterial canker is a common and widespread disease of stone fruit. The pathogen is usually present on leaves but does not affect or harm healthy plants until it comes into contact with an open wound. The pathogen can enter wounds caused by mechanical or natural means, especially after heavy storms or pruning. It affects all stone fruit, but apricots and cherries are particularly susceptible. Stressed or young trees are more vulnerable and may not recover if the infection is not treated at first sight.

Symptoms

Sunken dead lesions on trunks, branches or stems that may exude copious amounts of gum or sap. These lesions are usually slightly brown-red or yellow. If left untreated, cankers can girdle branches and kill the entire limb. If leaves are affected, water-soaked spots appear and eventually age, brown and become holes.

Plants Impacted

  • Stone fruit (apricots, cherries, nectarines, peaches and plums)

How to Protect Your Plants

Remove infected branches by pruning 100 mm below the canker – this will help reduce the potential of pathogens remaining on healthy plant parts. Bag and bin affected plant parts – do not add to compost or green waste.

Avoid pruning in winter as this is when the disease is most active. Sterilise and sharpen secateurs and prune branches in autumn before leaf fall or in spring after leaf growth has started. Ensure the conditions are dry, as wet weather can encourage spores to spread. To help prevent bacterial gummosis in apricots and cherries, spray with Yates Liquid Copper Fungicide in autumn, winter and spring. Feed trees well to improve overall health and vigour. Feed regularly with Yates Thrive Natural Citrus & Fruit Organic Based Pelletised Plant Food in late winter, mid-spring and mid-summer.

Yates Products

Yates Liquid Copper - suitable for use on apricots and cherries only.

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Image above: Rose Canker of rose. 
(Image courtesy of Elise Dando) 

What is Rose Canker

Leptosphaeria coniothyrium or Coniothyrium spp.

Rose canker - also known as Rose Dieback - is a common disease that affects rose stems and canes. It is caused by various fungal pathogens and occurs when the pathogens invade plant tissue through natural or mechanical wounds. The disease is most prevalent during the cooler times of the year and can also be spread by rain or water splash.  

Symptoms

Red spots appear on stems, later becoming black or brown. These cankers enlarge into brown sunken lesions with dark raised margins. Tiny black fruiting bodies are sometimes seen. Cankers can remain localised and eventually girdle the stem or move along the stem and kill the plant.

Plants Impacted

  • Roses

How to Protect Your Plants

Cankers often appear soon after pruning, particularly if secateurs were not sterilised between pruning and/or cuts were poorly made. See How to Prune Roses for best practices. Remove all diseased stems, cutting well below the canker.

There are no chemical treatments for rose canker. However, healthy rose bushes are better able to defend against canker attacks, so feed regularly with Yates Thrive Roses & Flowers Organic Based Pelletised Plant Food to help maintain health and vigour. Avoid overhead watering and mulch well with an organic mulch, keeping it away from the main stem.

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Image above: Cypress canker of Thuja sp.

What is Cypress Canker

Seirdium spp.

Cypress canker - also known as cypress dieback - is a serious fungal disease of conifers (Cupressaceae). The pathogen invades natural openings or mechanical wounds, destroys plant tissue, disrupts the vascular or sap system, and consequently kills off the branch beyond the wound. Branches can die-back rapidly – almost overnight – and can quickly kill the whole plant.  

Symptoms

Sunken red-brown lesions on branches or the main trunk, which often exude resin or gum through cracks or around the edges of the wound. There can be many infection sites along a branch. Small black fruiting bodies may be seen on the surface of the canker.

Plants impacted

  • Conifers (Cupressaceae)

How to Protect Your Plants

Remove infected plant parts, pruning at least 100 mm below the infection. Sterilise secateurs or shears between cuts to prevent the disease spreading. For severely affected plants, it’s best to completely remove and replace with an alternative plant.

There are no chemical treatments for cypress canker. However, by keeping plants healthy, you can improve their natural defences against canker attacks. Feed regularly with Yates Dynamic Lifter Soil Improver & Plant Fertiliser. Check for signs of pest/disease and treat if required. Extended periods of drought and extreme weather can weaken/stress established conifers – ensure they are watered well leading up to dry events and mulch well to help retain moisture.

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Image above: Phytophthora stem canker of Durian.

What is Phytophthora Stem Canker

Phytophthora spp.

Phytophthora stem canker is usually a secondary infection caused by Phytophthora root rot (see What is Root and Collar Rot). The spores of root rot pathogen splash onto natural openings or wounds on the trunk or stems, resulting in rots or cankers.

Symptoms

Sunken cankers form at the infection site, causing the bark to discolour and crack. Brown-red sap may ooze from the wound/s. If allowed to progress, cankers will cause branches beyond the infection site to die back. If the main trunk is affected, the canker can ringbark the tree and eventually kill it.

Plants Impacted

  • Avocadoes
  • Bananas
  • Citrus
  • Kiwifruit
  • Stone fruit, including peaches, plums and nectarines
  • Passionfruit
  • Tropical fruit
  • Nut trees, including macadamias and pecans

How to Protect Your Plants

Remove infected plant parts, pruning at least 100 mm below the infection. Sterilise secateurs or shears between cuts to prevent the disease spreading. Treat affected plants with Yates Liquid Copper after the removal of dead or affected tissue.

Healthy plants are better at resisting diseases than weakened plants. Feed fruiting plants regularly with Yates Thrive Natural Citrus & Fruit Organic Based Pelletised Plant Food. Avoid overhead watering and mulch well with an organic mulch, keeping it away from the main stem.

Yates Products

Yates Liquid Copper - suitable for use on Avocadoes, Bananas, Citrus, Kiwifruit, Lychees, Peaches, Plums, Nectarines, Passionfruit, Tropical fruit, Macadamias and Pecans.

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Image above: Citrus canker of citrus leaves.

What is Citrus Canker

Xanthomonas citri subsp. citri

Citrus canker is an exotic or introduced bacterial disease that is not currently present in Australia. It has been detected in the past, but has been successfully contained and eradicated. The pathogen attacks all parts of citrus, including leaves, shoots, twigs and fruits.

Symptoms

Warty brown lesions appear on the leaves, shoots, twigs and fruits. The spots usually appear along leaf margins or tips and have water-soaked edges that later turn into a yellow halo.

Plants impacted

  • Citrus

How to Protect Your Plants

If the disease is suspected, please notify the Department of Agriculture, Water and the Environment.


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