DISEASED TREES

Over the last few years Victoria has seen an extensive increase in the occurrence of Cypress Canker (Seiridium spp) / Cypress Dieback on various exotic Cypress trees.

Fungal spores enter a tree through wounds in the bark which could be pruning cuts, cracks, insect holes, storm damage to limbs etc. and interfere with the conducting system of the Cypress tree. The spores are usually spread by wind and water splash. Usual symptoms include dieback from the top of the tree down or selected branches browning and dying throughout the canopy, a branch can change colour over a period of days.

You may (but not always) see thin, elongated scourges on the stems, branches and branch axils. These scourges cause twig and branch dieback. Most scourges are wounds, slightly sunken, with raised margins, and they may be discoloured dark brown to purple. Cracked bark in infected areas is often accompanied by extensive resin exudates that flow down the diseased branches and trunk. The cambial tissue beneath oozing sites is discoloured with reddish to brown colour. Once most of the canopy has browned off that limb or that tree will almost certainly die. We believe the long period of dry conditions weakened the trees, particularly the root systems; they have then been hit with a period of above-average rainfall and optimum conditions for fungal attack. The trees have been damaged and stressed making them susceptible to dieback from a range of fungal diseases. It is highly likely that the disease is the secondary problem (the final straw) and the primary issue is tree stress which is making trees susceptible to attack.

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.

Trees affected

Monterey Cypress (Cupressus macrocarpa), Lambert’s Cypress (Cupressus lambertiana), Lawson’s Cypress (Chamaecyparis lawsoniana), Italian Cypress (Cupressus sempervirens), Arizona Cypress (Cupressus arizonica), False Cypress or Lawson’s Cypress (Cupressus lawsoniana), hybrids: x Cupressocyparis leylandii including cultivars ‘Castlewellan Gold’, ‘Leighton’s Green’, ‘Naylor’s Blue’, and ‘Swane’s Golden’. There are other susceptible species.

Less affected trees

Arizona Cypress (Cupressus arizonica), Mexican Cypress (Cupressus lusitanica), Bhutan Cypress (Cupressus torulosa), Western Red Cedar (Thuja plicata), Thuja occidentalis, Juniperu s virginiana.