Alder Tree Diseases


Alder trees (Alnus) are deciduous trees belonging to the Betulaceae family. There are approximately 35 species of alder trees, with the common alder (Alnus glutinosa), Italian alder (Alnus cordata) and gray alder (Alnus incana) being the most common. While alders tend to be hardy trees, they are still susceptible to a few diseases.

Common Diseases

Alder trees are most susceptible to the alder phytophthora disease (Phytophthora alni). They are also vulnerable to a fungal disease called artist's bracket (Ganoderma lipsiense).


Alder phytophthora causes stunted leaf growth, premature leaf drop and tarry spots to form on the tree's dying bark. Artist's bracket can cause root rot, butt rot and white rot, all of which impair the alder tree's stability.

Other Problems

Alder trees are vulnerable to several pests, including the alder leaf beetle (Agelastica alni), the common sawfly (Heterarthrus vagans) and the birch leaf-roller (Deporaus betulae).


Alder leaf beetle larvae eat large holes in the leaves, while sawfly larvae cause premature leaf drop. The birch leaf-roller causes the affected alder tree's leaves to brown and curl.


Since many alder tree diseases are caused by excess moisture, alders should never be planted in locations vulnerable to flooding. Prune out and destroy the infected leaves and limbs, to avoid spreading any infection.


  • Phytophthora Disease of Alder
  • Artist's Bracket
  • Alder Leaf Beetle

Who Can Help

  • Common Sawfly
  • Birch Leaf-Roller
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About this Author

Cat Carson has been a writer, editor and researcher for the past decade. She has professional experience in a variety of media, including the Internet, newspapers, newsletters and magazines. Her work has appeared on websites like and, among others. Carson holds a master’s degrees in writing and cultural anthropology, and is currently working on her doctoral degree in psychology.