Leyland Cypress Tree Problems

— Written By ascheck and last updated by

Many of Central North Carolina’s Leyland cypress trees have been dropping like flies in recent months. Unfortunately for this mighty evergreen tree there is no end in sight. The Leyland cypress, known to the scientific community as X Cuprocyparis leylandii is a large evergreen tree that grows extremely fast and has the potential to grow to well over 100 feet tall and almost half as wide. This species of tree originated from a hybrid cross of two North American conifers, the Alaskan cypress and the Monterey cypress, and is cherished as a hedge or screen due to its thick evergreen growth. The Leyland cypress is also sought after due to its extremely fast rate of growth. These characteristics coupled with its ability to grow in a wide range of soils and climates have made it one of the most widely planted trees in the landscape.

The popularity of the Leyland cypress may ultimately be what leads to its downfall.

What were once minor pest issues have since become major epidemics for the Leyland cypress. Cankers and needle blight that kill off portions of the tree frequently ail Leyland cypresses and often times lead to its untimely death. The shear amount of Leyland cypresses in the landscape has caused these deadly diseases to spread like wildfire, killing many trees. The close proximity that these trees are often planted in to form hedges and screens only makes the problem worse. In addition to those diseases an insect known as the bagworm feeds veraciously on the foliage of the Leyland cypress. Bagworms, whose cocoons often mistaken for cones, have the ability to defoliate trees in a matter of weeks.

With threats as serious as cankers, needle blight, and bagworms one would think that it’s a miracle that the trees have made it this long. Cankers and needle blight are both caused by different species of fungi, while bagworms are the caterpillars of certain species of moth. Cankers kill large portions of the tree at once causing the foliage to turn a bright red-brown, whereas the blight kills the needles of the tree spreading from the trunk outward. Normally, the fungi are kept at bay by hot dry temperatures. Unfortunately the wet and relatively cool spring we have experiences in combination with prevalence of the Leyland cypress in the landscape, often planted close together in hedges and screens, has created a perfect storm for the development of the fungus that ultimately causes the cankers and needle blight.  Additionally the South’s hot temperatures and the Leyland cypress’s shallow root system further weaken the tree’s natural defenses to these pests.

Thankfully for gardeners and homeowners everywhere there are some measures that can be taken in hopes of preventing and eradicating these troublesome pests. In order to help avoid the fungi that cause needle blight and cankers keep the trees as dry as possible. Also, avoid pruning when the trees are damp as this opens up areas that can be infected by these noxious fungi. Once established the fungi are hard to control, the fungus that causes needle blight can sometimes be controlled with a general garden fungicide. Sadly, little can be done if your tree has developed cankers, which usually prove to be fatal for Leyland cypresses. Removing and destroying damaged foliage can slow the spread of these conditions. However, one must be ever careful to avoid spreading the disease to other trees.

In order to prevent bagworms one may remove their brown cases from the tree in the fall and winter before the young hatch can prevent bagworms. Generations of bagworms feed on the same trees year after year, if you find cases or have experienced previous damage from bagworms you can expect another infestation. Once established bagworms may be controlled by any number of oral and systemic insecticides. Be on the lookout for bagworms in your Leyland cypresses as they are much easier to control early on before they get larger and eat much more of your tree. They hatch in the early spring and are active throughout the summer, but are most noticeable just before they undergo metamorphosis when they are largest and eating the most

If it is too late for your Leyland cypresses do not fear, there are many alternatives to Leyland cypress that can serve the same purpose within the landscape. ‘Green Giant” arborvitaes, Arizona cypresses, and Japanese cedars are all conifers that effectively play the same role in the landscape as a Leyland cypress. In fact, some of the aforementioned trees are so similar to the Leyland cypress that it is often difficult to distinguish them. However, many of the alternates to the Leyland cypress are much less susceptible to disease saving you money and lots of aggravation in the longer run. If you are considering using Leyland cypress as a screen planting or just want a large conifer for your landscape I would urge you to reconsider as the cases of these diseases have been on the rise in recent years.

With the plant diseases that seem to be running rampant among Leyland cypress recently it may not be the best tree to select for your landscape, but there is no need to begin removing any healthy trees that do not show any symptoms of attack. Practice as much preventative care as possible such as keeping your trees dry and removing infected trees before they can spread any pathogens or pests. If your trees do fall victim to cankers, needle blight, or bagworms treat the symptoms if possible and if not promptly remove the dying trees and replace them with a disease resistant alternative.

For more information on Leyland cypresses and the pests that affect them, contact N.C. Cooperative Extension, Lee County Center (919-775-5624).

Alec Check is doing a Horticulture Internship with North Carolina Cooperative Extension in Lee County this summer.

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