Quick Facts
- Individual branch dieback
- Oozing or sunken cankers on branches
- Yellowing then browning foliage on affected limbs
- Resin flow on bark
What Is Seiridium Canker?
Seiridium canker is a fungal disease, caused primarily by Seiridium unicorne and related species, that infects the stems and branches of Leyland cypress and other needled evergreens. In Georgia landscapes, it is widely considered the most damaging disease of Leyland cypress.
How to Recognize It
- Yellowing or browning of foliage on one or more top or lateral branches, often called branch flagging, while the rest of the tree still looks green.
- Thin, elongated, slightly sunken cankers (lesions) on twigs, branches, or the trunk, sometimes with a dark brown to purple discoloration.
- Sticky resin oozing from cracks in the bark along the cankered areas.
- Branch and twig dieback that progresses over time, eventually killing large portions of the tree.
- Bark in the cankered area may appear cracked or discolored compared to healthy bark.
Symptoms can appear at any time of year but are most often noticed in early spring. Disease progression accelerates during hot, dry summer weather, and cankers can enlarge up to three times faster on drought-stressed trees.
Why It Matters for Atlanta Trees
Seiridium canker is considered the most important and destructive disease of Leyland cypress in Georgia and can kill a significant portion of, or eventually the entire, tree. Because Leyland cypress is so commonly planted as a tall privacy screen near homes, fences, and driveways across Atlanta, declining trees can become a falling hazard, and the disease also affects Italian cypress, Arizona cypress, Monterey cypress, Eastern red cedar, and other needled evergreens used in local landscapes.
Why this needs an ISA-certified arborist
Seiridium canker looks similar to other Leyland cypress problems, including Botryosphaeria canker, bagworms, spider mites, and simple drought stress, and proper identification often requires close inspection of bark, resin flow, and canker shape. A certified arborist can confirm the diagnosis, prune infected wood correctly (cutting well below the canker and disinfecting tools between cuts to avoid spreading the fungus), and assess whether declining trees near a home pose a falling risk that warrants removal.
Suspect Seiridium Canker on your tree? Schedule a free on-site visit from EastLake's ISA-certified arborists at request a free estimate or call 404-850-1174.
General Prevention
- Water deeply around the base of the tree every 7 to 14 days during dry periods, since drought stress greatly accelerates canker growth.
- Apply a layer of mulch extending several feet beyond the lowest limbs to conserve soil moisture and protect roots, keeping mulch a few inches away from the trunk.
- Avoid crowding when planting Leyland cypress and similar evergreens so air can circulate and trees are not competing for water.
- Prune out and destroy infected branches well below visible cankers, and disinfect pruning tools between cuts to avoid spreading the fungus to healthy wood.
What NOT to Do
- Do not self-diagnose. Many tree problems look alike, and treating the wrong one wastes time and can harm the tree.
- Do not apply fungicides, insecticides, or other chemicals without an arborist's specific recommendation. Wrong product or wrong timing makes things worse, and fungicides are generally not effective once Seiridium canker is established.
- Do not prune symptomatic limbs without sanitizing your tools between every cut. Using contaminated pruners is one of the most common ways homeowners accidentally spread the fungus from a sick branch to healthy wood.
Related Services
For most diagnosis and treatment questions, the right starting point is one of our services:
- ISA-Certified Arborist Services: diagnosis, consultation, second opinion
- Plant Health Care (PHC): ongoing tree health management
- TRAQ Tree Risk Assessment: when the tree may be a safety hazard
Sources
This page summarizes general information from: UGA Extension (CAES Field Report, Bulletin 1229), Alabama Cooperative Extension System (ACES), and University of Maryland Extension.