Cypress decline

A large number of dead and dying cypress trees have been observed in rural Victoria in recent years.

Department of Economic Development, Jobs, Transport and Resources (DEDJTR) investigations in south and west Gippsland, the Mornington Peninsula and the Western District have found trees affected by various fungal pathogens, in particular cypress canker (Seiridium species), but also Botryosphaeria, Phomopsis and Pestalotiopsis species.

These fungi can all cause dieback symptoms, especially when environmental conditions have placed trees under stress. They are a mixture of primary pathogens (which can attack intact plants) and secondary pathogens (which usually attack plants at sites where another infection already exists).

DEDJTR believes that the last drought weakened the cypresses and left them vulnerable to infection. Disease development has also been favoured over the past 12-18 months by waterlogging and/or warm, humid conditions in some areas.

Cypress canker is the most significant of the pathogens currently affecting exotic conifers in Victoria. Unfortunately there is no proven cure for this disease.

Cypress canker attacks at least 25 conifer species of the Cupressaceae family in many parts of the world, including Australia, the United States and Europe.

It is not known to affect other plant families.

Previously this disease was thought to be caused by a single Seiridium species, but scientists now believe that three species (S.cardinale, S.cupressi and S.unicorne) can cause the same symptoms.

These fungi have been present in Victoria for more than 50 years.

How does cypress canker infection occur?

Cypress canker infects a plant through spores (conidia) which are carried on the wind, in water droplets or by insects. Spores that land on healthy foliage can germinate under warm, moist conditions and infection occurs through natural fissures in the bark or through scars caused by mechanical damage (e.g. pruning, animals or falling branches).

The pathogen then girdles twigs, branches and the main trunk, interfering with the sap-conducting system and causing the foliage to die. Death may occur progressively from branch to branch.

New local infections can also develop when spores are washed down the tree or splashed from tree to tree by rain or overhead irrigation. They can also be transferred from plant to plant on pruning tools, or through the transport of infected cuttings or plants.

Symptoms

Figure 1. Cypress cankers and resin on a Leyland cypress. Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org

After the initial infection, the fungus kills the plant's vascular tissue, causing characteristic sunken, lens-shaped cankers and ringbarking. This interferes with the vascular system of the tree and eventually causes death above the wound. Generally, older trees are more susceptible but any tree is susceptible if in a stressed state (e.g. through drought, waterlogging or poor nutrient status).

Reddish cankers form at the infection site and resin often exudes from around the edges of the cankers or through cracks in the bark (Figure 1). Individual cankers can be elongated and there may be many along each infected branch.

The spore-producing structures of the fungus can be identified on the surface of the bark as small, circular, black dots on the canker surface.

Branches die rapidly, yellowing almost overnight as the foliage is starved of sap (Figure 2). If the infection is not managed, it can eventually lead to the death of the whole plant.

Hot, humid weather, drought and insects (e.g. bark beetles) can hasten the decline of trees infected with cypress canker, due to splitting bark and poor wound responses from the tree.

Species susceptibility

More than 25 conifer species can be affected by cypress canker, but susceptibility varies between the species.

Susceptible species:

• Cupressus macrocarpa (Monterey cypress) (susceptible < 10 years old)
• Chaemaecyparis lawsoniana various cultivars
• x Cupressocyparis leylandii 'Castlewellan Gold'
• x Cupressocyparis leylandii 'Leighton Green'
• x Cupressocyparis leylandii 'Naylors Blue'
• Cupressus sempervirens 'Swanes Golden' and other cultivars
• Cupressus torulosa.

Less susceptible species:

• Cupressus lusitanica (variable susceptibility)
• Cupressus arizonica (Arizona cypress)
• Calocedrus decurrens
• Thuja plicata (western red cedar)
• Thuja occidentalis
• Juniperus virginiana.

Management

Management of cypress canker is the responsibility of the land owner/manager.

In significantly affected trees, replacement with known tolerant cypress species or varieties (see above) may be the only long-term option.

Cypresses can also be replaced with unrelated plant species, such as Australian natives, including for use as shelterbelts.

In re-planted or existing cypresses, canker damage can be minimised by ensuring trees are well-sited and well-managed; for example:

• Avoid planting susceptible species on disease-prone sites, such as those with high levels of nitrogen.
• Keep trees healthy to improve their natural defences against an initial infection. If fertilisers are required, they should be evenly distributed around the drip line of the trees. Watering may be needed during dry spells.
• Reduce the chances of branch or stem wounding e.g. by fencing off trees from livestock.
• Prune infected branches a minimum of 10 centimetres below the canker to help prevent infection spreading to the main stems (but take care not to over-prune). Pruning should preferably be done in winter or following dry weather, when spores are less likely to infect pruning wounds. After pruning, wound dressings may help to prevent spore infection. All pruning tools should be sterilised before and after use with either alcohol or dilute bleach.
• Remove and destroy severely diseased plants by deep burial or burning to help to reduce the risk of neighbouring trees becoming infected.

Chemical use

There are no fungicides registered for the control of cypress canker and limited science about off-label options.

Off-label use of fungicide protectants is only likely to be of value on trees without obvious signs of infection and should only be undertaken if the user understands the risks associated with off-label chemical use. See Off-label use.

For enquiries about chemical use, contact your local DEDJTR Chemical Standards Officer – telephone 136 186.

Movement of host plant material

Cypress canker is not a regulated disease in Victoria and there are no legal restrictions on the movement of host plant material. However, to minimise the risk of spreading the disease, infected material should not be moved from the property unless it is covered or in a sealed container.

Reporting

If you wish to report cypresses affected by disease, please forward the details to plant.protection@ecodev.vic.gov.au and attach photographs if possible.

Reports of disease on public land can be directed to the relevant authority.

If you wish to have a suspected case of cypress canker diagnosed, you can contact DEDJTR's Crop Health Services on (03) 9032 7515 or chs.reception@ecodev.vic.gov.au and arrange to submit a sample. A fee applies.

References and further reading

• Cunnington, J.H. (2007) Seiridium cupressi is the common cause of cypress canker in south-eastern Australia. Australasian Plant Disease Notes, 2, 5355
• Graniti A. (1998) Cypress canker: a pandemic in progress. Annual Review of Phytopathology 36, 91114. doi: 10.1146/annurev.phyto.36.1.91
• Hansen, E.M. and Lewis, K.J. (1997) Compendium of Conifer Diseases. APS Press. The American Phytopathological Society. Lunn, M. (2004) Fact Sheet: Cypress Canker ABC Gardening Australia
• Reid, A. (2004) Cypress Canker (caused by Seiridium spp.) Department of Agriculture and food. Government of Western Australia. Note: 13
• Sydney Royal Botanic Gardens Trust Fact Sheet on Cypress Canker