Leyland cypress trees (Cupressocyparis x leylandii) are valued for their majestic height, evergreen needles and varied uses. Their mature height reaches up to 50 feet, providing privacy fencing far above what wooden and metal fences allow. Insects and diseases may attack trees and cause foliage to turn brown, which mars their beauty and function.
Growing in U.S. Department of Agriculture plant hardiness zones 6 through 10, Leyland cypress is a fast-growing tree, commonly growing up to 4 feet per year. Their pyramidal form resembles fence posts that fill in spaces between trees with greenery. Their high tolerance for salt spray makes them good choices for coastal regions. As a windbreak, Leyland cypress offers protection to plants and structures from strong winds that buffet them. Soft evergreen needles dress its flattened branches.
Larvae of the Theridopteryx ephemeraeformis moth are commonly called bagworms because of the structures they make. They weave cypress needle fragments with silken strands to form bags, or cases, that they attach to trees. Inside the bags, which provide camouflage because of the needle coverings, larvae pupate into adult moths. Larvae feed on needles, causing them to turn brown as they remove green chlorophyll. Spruce spider mites (Oligonychus ununguis) spin webbing in Leyland cypress trees that they use as defense mechanisms instead of as methods to capture prey. They feed by extracting needle sap through sharp mouthpieces. Yellow, stippled leaves are the first signs of mite damage, and brown needles indicate heavier infestations. Although pesticides kill bagworms and spider mites, mature tree height prohibits thorough spraying.
Leyland cypress succumbs to two primary canker diseases, also called dieback. Fungal pathogens that enter through tree bark cause bot (Botryosphaeria dothidea) and seridium (Seridium spp.) cankers. Since the 1980s, when seridium canker was discovered on Leyland cypress in California, this disease has spread rapidly to infect trees throughout the United States. Lesions form on twigs and branches that girdle branches and cut off nutrients to limbs. As branches die, needles turn brown at the ends of limbs. Fungicides may help when trees are small, but the tall height of mature Leylands makes thorough spraying impractical.
Cercosporidium needle blight, also called cercospora, is a fungal disease caused by the pathogen Passalora sequoiae. Initial damage starts on needles that are close to tree trunks on lower branches, before the diseases moves outward and upward. Entire lower canopies may turn brown, leaving only a small section of green needles at tree tops. Persistently wet foliage from heavy rainfalls and overhead irrigation exacerbates needle blight disease. Although mature tree height makes it prohibitive to spray trees thoroughly, the Clemson Cooperative Extension recommends treating small trees with fungicidal sprays to manage the disease.
- University of Florida IFAS Extension: X Cupressocyparis Leylandii -- Leyland Cypress
- Alabama Cooperative Extension System: Canker and Dieback Diseases of Leyland Cypress
- Clemson Cooperative Extension: Leyland Cypress Diseases and Insect Pests
- California Polytechnic State University Urban Forest Ecosystems Institute: Leyland Cypress
- Alabama Cooperative Extension System: Cercospora Needle Blight on Leyland Cypress
- University of Nebraska-Lincoln Extension: Bagworms
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