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My Leyland cypress hedge has Seiridium unicorne canker fungus. The photo you see is one of many Leylands in my yard. I often regret my decision to plant the species but I also wish I had reviewed this material before I planted
Underneath that spot of dead foliage is a seiridium canker, also called coryneum canker, and is a big problem on Leyland cypress (Cupressocyparis leylandii) trees. The fungus will destroy the cypress' form and cause eventual death if not controlled.
Seiridium canker is usually localized on individual limbs and should be removed immediately. If you control this situation early, you can improve the condition of the tree and its future outcome. If you leave it for another day, you will regret it.
Fungal spores from an active canker are often washed down the tree or splashed from tree to tree by rain or overhead irrigation. New infections develop when spores lodge in bark cracks and wounds and this process quickly overwhelms the tree.
So, seiridium canker fungus is a major problem owners of Leyland cypress, especially in the southeastern United States. Cankers can be identified as sunken, dark brown or purplish patches on limb bark and there us usually excessive resin flow from the patch. It should be recognized that resin flow can occur from the branches and stems of trees that do not have the disease.
Other diseases like Botryosphaeria cankers, Cercospora needle blight, Phytophthora and Annosus root rots can have very similar characteristics. Be careful not to use resin flow alone as a diagnosis for Seiridium canker.
The uncontrolled canker over time will destroy the cypress' form and eventually cause the tree's death. Seiridium canker is usually localized on individual limbs and shows mostly as dead foliage (see attached photo).
In many cases, the canker will disfigure and damages trees, most particularly in hedges and screens that are heavily pruned. The limb is usually dry, dead, often discolored, with a sunken or cracked area surrounded by living tissue (see attached photo). In many cases there is a gray discoloration at the point of infection. The foliage dies beyond the canker point to the limb tip.
Disease Prevention and Control:
Provide adequate space when planting trees to prevent the stress of crowding and to increase the air circulation. Planting at a minimum of 12 to 15 feet between trees may look excessive but will pay off in just a few years.
Do not over-fertilize trees and mulch under trees to at least the drip line. These recommendations will minimize stressful water loss and the ever-present competition for water from surrounding plants. as well as potential damage to trees from lawn mowers and string trimmers.
Prune away the diseased branches as soon after they appear as possible. Make the pruning cuts 3 to 4 inches below the diseased canker patch. You should always destroy diseased plant parts and try to avoid physical damage to plants.
Sanitize pruning tools between each cut by dipping in rubbing alcohol or in a solution of 1 part chlorine bleach to 9 parts water. Chemical control of the fungus has proven to be difficult but some success has been noted with a full-coverage fungicide spray at monthly intervals from April to October.