The susceptibility of conifers varies.
Susceptible species
- Cupressus macrocarpa (Monterey Cypress) (most susceptible when less than 10 years old)
- Chaemaecyparis lawsoniana – various cultivars
- x Cupressocyparis leylandii ‘Castlewellan Gold’
- x Cupressocyparis leylandii ‘Leighton Green’
- x Cupressocyparis leylandii ‘Naylors Blue’
- Cupressus lusitanica
- Cupressus sempervirens ‘Swanes Golden’ and other cultivars
- Cupressus torulosa
Less susceptible
- Cupressus arizonica (Arizona cypress)
- Calocedrus decurrens
- Thuja plicata (Western Red Cedar)
- Thuja occidentalis
- Juniperus virginiana
Symptoms
Seiridium canker may be caused by one of three Seiridium species (Seiridium cardinale, S. unicorne or S. cupressi). Seiridium is essentially a weak pathogen requiring some defect by which to enter. Thus spores may enter the tree through fine bark cracks which develop naturally in branch and twig crotches or through other wounds in the bark such as those made by borers or sap sucking insects. Pruning wounds and other injuries also provide a point of entry.
The fungus interferes with the sap-conducting system, eventually causing death of the branch or main trunk above the wound. Older trees are usually more prone to this disease but any tree is susceptible if stressed, for example, by drought or poor nutrient status.
Many of these species are planted, for hedging, shelter, screening or as specimen trees due to their adaptability to a range of soil conditions and the range of shapes and sizes available.
When branches become infected the fungus effectively ringbarks the limb so the foliage yellows and dies from the tips back. Gold varieties gradually lose colour and become brown. Typically, branches scattered throughout the tree may be affected. Commonly the disease starts at the top of the tree.
Branches die rapidly, yellowing almost overnight as the foliage is starved of sap. If untreated, the disease will eventually lead to the death of the whole plant. This may take a few months or a couple of years.
In the early stages, dark brown or purple patches appear on the bark. Tiny black, circular fruiting bodies may be visible on the bark surface, which is often cracked. Sunken cankers, with a reddish tinge, form at the entry point of the fungus, and resin often exudes from the edges of the cankers or through cracks in the bark.
Wood underneath the bark develops a reddish-brown discolouration.
Individual cankers are long and thin and may be numerous along a branch. Stems with large cankers are prone to breakage in high winds.
Once the plant is infected and weakened with Seiridium, it is more susceptible to other pests and diseases, especially borers.
Phytophthora root rot may occasionally present a similar pattern of branch death but cankers are not produced.
Disease spread
Spores are carried on the wind, in water droplets or by insects and birds. New infections 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.
Control
Healthy plants are better able to resist infection so it is important to feed plants regularly and water during dry periods. The application of sprays to prevent insect attack may also reduce the chance of infection through those wounds. Infected branches should be pruned 10cm below the canker to prevent infection spreading to the main stems. Tools should be sterilised before and after use with alcohol or dilute bleach. Severely diseased plants should be removed and destroyed.
No fungicides are currently registered for the control of Seiridium on conifers but copper based fungicides are used as a preventative in spring on smaller trees. Phosphorous acid (phosphite) is widely used as a control. Apply treatments in spring and early summer to the infected tree and its neighbours and repeat eight to ten weeks later. Apply a minimum of 1ml of active ingredient per metre of canopy for prevention and use a higher rate for affected trees, following package directions. Use 20ml syringes for trunk injection on big trees, spacing the injections around the trunk.
Unfamiliar pests
The Department of Primary Industries and Regional Development (DPIRD) is on the lookout for animal and plant pests, diseases and weeds that could pose a threat to agriculture and the environment.
If you discover something unfamiliar, please note the location, take notes on the situation and send a photo to the Pest and Disease Information Service (PaDIS) by email: padis@dpird.wa.gov.au or phone them on (08) 9368 3080.
Please read the sending specimens for identification webpage before sending, or bringing in, samples to the Pest and Disease Information Service, 3 Baron-Hay Court, South Perth, 6151, WA.