Prevention & Treatment: When planting as a screen, provide enough space (a minimum of 12 to 15 feet) between trees for good air circulation and to minimize stress as they mature and enlarge. From the point of infection until the development of cankers and other symptoms often takes years. Spores can be spread (within the tree and to new trees) via rain, overhead irrigation, and pruning tools, typically entering the trees through wounds and cracks in the bark. Spore-producing structures of the fungus appear on the surface of the canker as small, black dots that are barely visible without a magnifying lens. The fungus survives winter in infected tissue. Oozing sap is a symptom of Seiridium canker and dieback.Įnvironmental conditions that stress Leyland cypress (especially drought, but also spring freeze damage) favor the development of infection. If the fungus gets into the main trunk, it can kill the entire tree. Generally, the discolored branches are the symptom noticed first. When a cankered branch has only recently shown a change in color, needles will fall off easily when a hand is run along the branch. They are often yellow to grayish tan to reddish-brown in color and usually appear randomly distributed on the tree. Branches affected by Seiridium canker experience dieback. A shallow cut at the site of the canker typically reveals tissue beneath the bark that is reddish to brown in color and sticky. However, resin flow by itself is not a defining characteristic of this disease as it often occurs in otherwise healthy Leyland cypresses. In addition, the cankers are often accompanied by an extensive flow of resin from cracks in the bark. Instead, multiple cankers form around a branch, reducing water flow significantly. A single Seiridium canker does not enlarge to girdle a branch. They are often thinly elongated, shallow, and the surrounding bark shows a dark brown to purplish discoloration. More specifically, Seiridium cankers form on stems, branches, and in branch axils. Generally speaking, cankers are dark, oval or elongated lesions that are usually dry, may be sunken with a raised edge, and are surrounded by living tissue. Seiridium Canker/Dieback: In the Southeast, this disease is caused most often by the fungus Seiridium unicorne. For further details on providing a Leyland cypress with the conditions under which it grows best, see HGIC 1013, Leyland Cypress. In general, Leyland cypress requires full sun and prefers moderately fertile soil that is moist and well-drained. Ultimately, a vigorously growing plant is always better able to survive disease and insect problems than is a stressed one. With the increased planting that has resulted from its popularity, various diseases and pest problems have become more evident.Īs with any plant, the first step to a healthy Leyland cypress is to provide it with the cultural conditions that it needs. Leyland cypress (x Cupressocyparis leylandii) has grown in popularity in the Southeast over the last few decades, especially in its use as a fast-growing screening plant.
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