Conks

Conks are woody, shelf-like structures produced by some fungi. These fruiting bodies are often seen on trees and can indicate fungal diseases, such as canker rot or butt rot.

Canker rot conks (Joseph OBrien, USDA Forest Service, Bugwood.org) CC BY 3.0 US

Polypores

Conks are the reproductive form of a large group of fungi known as polypores. Polypores are found in the bark, trunks, and branches of trees, though some are in the soil. Polypores are the primary players in wood decomposition, so their presence often indicates decay. Polypores are important in nutrient cycling, so they aren’t all bad. This group is large and diverse, but they all have conks in common.

The conk clan

This group is defined by how they grow rather than genetics, so it is very diverse. The most common types of conks include:

• Artist’s conk
• Beefsteak fungus
• Birch bracket
• Dryad’s saddle
• Sulfur shelf
• Turkey tail

Turkey tail conk (Public Domain)

Conk structure

Also known as bracket fungi, or shelf fungi, this group (Basidiomycota) produces circular, shelf-shaped fruiting bodies that can appear in rows, columns, or singly. Basidiomycetes are the only fungi known to break down lignin. Lignin is what makes trees rigid. The disease that accomplishes this feat is known as white rot.

White heartwood rot conk (Dave Powell, USDA Forest Service, bugwood.org) CC BY 3.0

Some conks are annuals while others are perennials, Some conks can live for 80 years or more. In either case, they tend to be leathery, sturdy growths. These growths produce spores, called basidiospores, in pores found on the underside of the conk.

Sulfur shelf conk (Robert L. Anderson, USDA Forest Service, Bugwood.org) CC BY 3.0

Conks grow directly out of the wood on which the fungi feed. If you were to cut one open and look at it closely, you would see two layers: a tube layer and a supporting layer. The tubes are honeycomb-like structures lined with a spore-forming surface called the hymenium. The supporting structure creates the shelf and its attachment to the tree.

The problem with conks is that their presence indicates that fungi have taken up residence in your tree. If your tree has conks, the first step is identifying the type. Some fungi are worse than others.

Artist’s conk (Dave Powell, USDA Forest Service, bugwood.org) CC BY 3.0

Beefsteak fungus (João Loureiro, Associação Florestal do Douro Norte, Bugwood.org) CC BY 3.0 US

Preventing fungal conks

The fungi that produce conks enter trees through mechanical wounds, damaged roots, broken or rubbing branches, frost cracks, sunburned bark, and improper pruning cuts. Fungal spores travel on the wind, rain, and on birds and insects, so keeping your tree’s protective outer layer intact is the best prevention. The following tips should help with that:

• Leave clean cuts when pruning.
• Prune and train trees for good airflow and structural strength.
• Do not use pruning sealants (which seal in moisture and pathogens).
• Avoid digging or rototilling around trees.
• Provide good drainage.
• Protect trees against damage from weedwackers, lawnmowers, and car doors.
• Whitewash exposed branches and trunks.
• Remove tree supports as soon as they are no longer needed.
• Ensure that sprinkler spray does not hit tree trunks.

​If you have a tree with conks, you should probably contact a certified arborist. They can inspect the tree for structural integrity and to determine the extent of the infection.

Conks may look cool, but you don’t want them on your trees.