The recent popularity of the Leyland Cypress (Cupressocyparis leylandii) is now plagued by the realization among gardeners and landscapers that planting such trees will likely invite an array of future problems. Once hailed across the Northeast and South as the ideal evergreen tree for screen plantings, the susceptibility of Leyland Cypress to certain diseases and insect pests has led horticulturalists to recommend substitutes, such as the Crypotomeria, or Japanese Cedar. The Leyland Cypress grows rapidly, up to 70 feet.
When older foliage on the inside of a Leyland Cypress begins to yellow and eventually brown, Seridim canker is often the culprit. The fungal disease will cause sunken cankers on the bark. The cankers appear purple, red or dark brown. Normally the disease will kill lower branches first, and then progress up the tree. Seridium canker can't be cured with chemical treatments. Prevent the infection by protecting the bark from wounds where the fungus can enter the tree. Remove diseased branches below the infection point and prune the tree to promote adequate air flow.
Poorly drained soils and excessive watering are the most common cause of fungal root problems. Don't plant Leyland Cypress trees too deeply, because they have shallow root systems. Root rot diseases, like Phytophthora, turn roots black and spongy. Once the gardener discovers a root rot problem, it's normally too late to save the tree.
Leyland Cypress trees produce fairly small cones. Large cone-shaped objects hanging from Leyland Cypress branches should signal a problem. Bagworms are moth larvae that create silk to build cone-shaped “bags” out of foliage and bark from the trees they infest. Unchecked, the pests can often defoliate a tree within one season. Pluck off the bags and destroy them if their presence is discovered early. Chemical insecticides are most effective in the early spring. Follow the chemical label and spray the foliage of the entire tree. The worms feed on the foliage and will die. The bags are virtually impenetrable. Spraying them is a waste of time.