brown branches on leyland cypress

Flagging on branches due to Seiridium canker. Photo: Jennifer Olson, Oklahoma State University,

Updated: February 27, 2023

Winter cold injury can lead to greater infections from fungal diseases, such as Seiridium canker.

Winter cold injury can often lead to greater infections from a few common fungal diseases that affect foliage, stems, and branches such as Seiridium and Botryosphaeria cankers, as well as Cercospora needle blight. Symptoms of canker diseases include branches that start to turn yellow to reddish-brown. Closer examination will reveal slightly sunken cankers, with resin exuding profusely several feet down on the infected branch, usually closer to the main trunk.

The fungal cankers spread primarily by releasing spores during rainy spring weather. The rainwater will carry the fungal spores to other branches. Infection on multiple branches throughout the tree or on the main trunk can kill the entire tree. The only known cure for Seiridium or Botryosphaeria cankers is pruning the infected branch below the infected area.

In the future, it would be best to diversify evergreen borders with a variety of evergreens and deciduous plant selections rather than just one species.

By Dr. Dave Clement, Principal Agent, University of Maryland Extension, Home & Garden Information Center.