Over the last 20 years, massive walls of green have been constructed across the Georgia landscape. These walls are not constructed of wood, steel or concrete. Rather, they are living walls “constructed” using the popular Leyland cypress tree.

Leyland cypress is the industry standard for creating a privacy screen to hide unwanted views, muffle street noise or to simply create a secluded outdoor living space. These trees are fast-growing, inexpensive and have a dense canopy of attractive green needles.

Unfortunately, Leyland cypress has been found to be susceptible to a number of pest problems. If you have Leylands in your landscape, you may have experienced a bagworm infestation or perhaps spider mites. While these can be difficult to control, they pale in comparison to a fungal disease called Seiridium canker.

In my experience, Seiridium canker, caused by Seiridium unicorne, is the most damaging disease for Leyland cypress. Plants of all sizes and ages are affected. Cankers may form on stems, branches and in branch axils causing twig, branch or — at least on smaller plants — stem dieback.

Cankers appear as sunken, dark brown or purplish patches on the bark, often accompanied by extensive sap flow. Scattered twigs or branches killed by the fungus turn bright reddish brown and are in striking contrast to the dark green, healthy foliage.

Fruiting bodies of the fungus appear on the bark surface of the cankers as small circular black dots barely visible to the naked eye. Spores of the fungus are spread to other parts of an infected tree, or from tree to tree by splashing water from rain or irrigation. The fungus also can be spread from tree to tree on pruning tools.

Seiridium canker is encouraged when Leyland cypress trees are under stress — most often the result of drought stress. Infection requires a wound, but it is also believed that the fungus can enter through lenticels (natural openings on the branches that allow for air exchange. As a result, Seiridium cankers often appear randomly distributed across the tree canopy, with foliage color ranging from yellow to light tan to brown.

Regular watering during extended drought does lessen the chance of disease. If a row of Leylands is planted, the easiest way to accomplish this is with a soaker hose. Simply run the hose down the length of the row, placing it a few inches from the trunks. Allow it to run for three to four hours once a week.

Remember, a soaker hose only emits 1 gallon of water per foot of hose per hour, so you are not using a lot of water.

According to Extension pathologist Jean Williams-Woodward, “The one thing that has to be stressed is that the infection occurred years ago, and it is only now after the cankers have enlarged that the symptoms are evident. Therefore, fungicides are not effective in controlling the disease at this time.”

If the tree is severely affected, Williams-Woodward said, “The best control is to remove the damaged tree and replant with something else or even another Leyland if that is what is wanted. Within a few years, the trees grow so fast that the loss of one will hardly be noticed.”

 Billy Skaggs is an agricultural agent and Hall County extension coordinator. Phone: 770-531-6988. Fax: 770-531-3994.