In recent weeks, I have received calls about Leyland Cypress trees turning brown across the county. Several factors can cause this, but it all begins at the beginning of how the tree was created. Originating as a hybrid in 1888 in Wales, UK, the Leyland Cypress is a cross between Alaska Cedar and Monterey Cypress. Known for its rapid growth and resilience to pruning, it quickly gained popularity as a favored choice for creating natural barriers in landscapes. Its ability to thrive in diverse soil conditions further contributed to its widespread use. Both the Alaskan Cedar & Monterey Cypress are native to the West Coast of the US, however, on different ends and would not have naturally crossed without human intervention.
Typically utilized as border trees, Leyland Cypresses are often planted closer together than recommended. On average, they can have a 20’ width, and close planting limits airflow between trees and increases competition for soil resources. This compromised environment makes the trees susceptible to various diseases.
Leyland being used as a screen, planted to where they do not need to compete for resources and have adequate airflow - reducing stress and disease on the tree. Clemson Cooperative Extension
One of the more common diseases affecting Leyland Cypress trees is needle blight, caused by the fungus Passalora Sequoia. This condition starts through the browning and shedding of needles, starting from lower branches and progressing towards the tips. Effective management involves ensuring adequate airflow around the trees when planting and the application of fungicides containing active ingredients like thiophanate-methyl and myclobutanil may help (be sure to read the pesticide label before using!!).
Needle Blight on Leyland. John Ruter, University of Georgia, Bugwood.org
Cankers on limbs and trunks, caused by weather stress such as drought, can also affect the Leyland’s. The more prevalent canker disease is Seridium Canker and, unfortunately, there is no control for this other than pruning. It is recognizable by the death of the limb or needles past the canker. The canker will appear as a dark red or brown spot and tree sap will be present. When pruning the affected area, cut the canker and be sure to sterilize your cutters between cuts to prevent the disease from spreading.
A pest affecting Leyland Cypress trees is the Bagworm, which is often mistaken as cones. They are identified as cylindrical bags hanging from branches. Controlling Bagworms involves physical removal during winter to prevent heavy infestations.
Bagworm. Chazz Hesselein, Alabama Cooperative Extension System
To maintain healthy Leyland Cypress trees, it all begins when you plant. Ideally, trees should be spaced at least 15’-20’ apart to ensure adequate airflow and reduce competition for resources, causing stress. Considering a variety of plants like Green Giant Arborvitae or Japanese Cedar can also help diversify the landscape and deter pests and disease.
