Conks

Conks are woody, shelf-like structures produced by some fungi. These fruiting bodies are often seen on trees and they 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
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Conks are the reproductive form of a large group of fungi known as polypores. Polypores are mostly found in the bark, trunks, and branches of trees, though some are found in the soil. Polypores play major roles in the decomposition of wood, so their presence often indicates decay. Polypores are also important in nutrient cycling, so they aren’t all bad. This is a large, diverse group but they all have conks in common.


The conk clan

This group is defined, not by genetics, but by growth behavior, 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)

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Conk structure
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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 and hard. 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

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

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

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Conks appear to 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, and the supporting structure creates the shelf and its attachment to the tree.


The problem with conks is that their presence indicates that some sort of fungi has taken up residence in your tree. If your tree has conks, the first step is to identify 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

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Preventing fungal conks

The fungi that produce conks generally enter trees through mechanical wounds, damaged roots, broken or rubbing branches, frost cracks, sunburn damaged bark, and improper pruning. 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. This means you should:

• leave clean cuts when pruning
• prune and train trees for good air flow 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

Birch conk (Joseph O'Brien, USDA Forest Service, Bugwood.org) CC BY 3.0

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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.