Leyland cypress (x Cupressocyparis leylandii) is a dense, pyramid-shaped, evergreen coniferous tree that rapidly grows to a height of 100 feet, or more. Leyland cypresses are hardy to USDA hardiness zone 6 and prefer full sun and well-drained soils. Leland cypresses are relatively disease-free, especially in the Southeastern U.S., according to Clemson University extension, but several insect pests affect this tree.
Spruce Spider Mite
Spruce spider mites (Oligonychus ununguis) are very small, and not seen easily without a microscope. Spider mites suck plant sap and cause speckling (tiny yellow spots) on needles and may cause browning and needle drop. Heavy infestations can result in fine webbing visible on the tree. Natural enemies of spider mites help to control infestations--only use insecticides for severe infestations. Avoid harming beneficial insects like predator mites, ladybugs and other insects, if possible.
Bagworms (Thyridopteryx ephemeraeformis) feed on Leyland cypress trees, resulting in a loss off needles. Growth of Leyland cypress is slowed with mild infestations, but heavy infestations can kill the tree. According to Clemson University Extension, bagworms often appear like cones on the tree, but are brown or green cone-looking, approximately 2 inch long sacs that fill with bits of plant material as larva feed. Remove cone-looking bags or spray with bacterial insecticide, or other horticultural insecticides to control bagworm. Use caution and read labels carefully when using commercial insecticides.
Immature forms of juniper scale (Carulaspis juniperi) crawl and settle on needles of Leyland cypress and feed by sucking plant sap. Eventually, a crusty shell forms over their bodies and they remain in one location. Symptoms of juniper scale infestation include the tree appearing off-color and branch growth slowing down. Needles turn brown or yellow over time, branches may die back and tree death can occur if scale is not controlled. Adult pests are white, gray or black (depending on age), mostly flat and appear as tiny bumps or scales underneath needles. Control the adult form with a horticultural oil spray in late winter or very early spring. Control juniper scale "crawlers" with products such as horticultural oil, insecticidal soap and commercial insecticides.