Seiridium Canker of Leyland Cypress

By on October 1, 2015

Landscape & Garden Editor Kevin Johnson Talks About Diagnosing and Treating One of Our Landscape Favorites

Leyland Cypress, x Cupressocyparis leylandii, is a very common and popular landscape tree used throughout the Appalachian area. This coniferous evergreen is often used for screens and hedges due to its fast growing nature. Leyands can easily grow 4-5 feet in a year. They have been relatively easy to care for with little to no disease problems except maybe the rare bagworm infestation. Things have certainly changed. We receive as many calls from folks concerned about Leyland Cypress as we do for Hemlock Woolly Adelgid. Because the Leyland Cypress is commonly found in our landscapes, it’s important to understand what’s happening to them.

Several years ago I attended an industry conference. During one of the seminars the speaker from U.G.A covered Seiridium Canker of Leyland Cypress. This was the first time I heard of this disease. Over the next few months I started paying attention to Leyland Cypress and things became very apparent. A tree that was virtually maintenance free was in trouble.

Seiridium Canker is possibly the most damaging disease affecting Leylands damaging small newly planted specimens and large mature trees alike. Cankers, which appear as sunken darkish brown or purplish patches on the bark, form on stems and branches causing dieback. Often homeowners mistake the cankers for bark boring insects, sadly, this is hardly ever the case. Dead branches turn brown and disease spores rapidly spread to uninfected parts of the Cypress or to uninfected trees by rainwater and irrigation. Seiridium Canker can also be spread through pruning.

Currently there are no chemical control measures to treat Seiridium Canker so spraying fungicides on infected trees simply doesn’t work. We do recommend pruning out infected limbs, although pruning is sometimes impossible on very large/tall Leylands. As always, be sure to sterilize your loppers or pruning tools between cuts using a 1 to 9 bleach – water solution. For new landscapes, providing proper spacing between trees will allow for air flow, reducing the risk of the pathogen spreading from tree to tree as easily. Avoiding stress by watering Leylands during times of significant drought and avoiding tree wounding also helps to reduce the risk of infection. The good news is I’ve seen very mature Leyland’s develop Seiridium Canker and continue to survive.
There are also several other cankers and root rot issues affecting the Leyland Cypress that may present to the homeowner as Seiridium Canker. Therefore, it’s always important to get the right diagnosis so that you can address the problem correctly.

For additional reading on the subject visit:

Kevin Johnson is the owner of Green Leaf Lawn and Ornamental, LLC, based in Blue Ridge. For more information about the devastating hemlock woolly adelgid and treatment options, Kevin can be reached toll free at 866-883-2420 or by email at 
Or check out his web site at or visit for more info.