Butt Rot

Butt rot? Really?
 
Yes, Virginia, there is a fungal disease of almond trees called butt rot. Its full name is Ganoderma root and butt rot, and it can kill your tree.

Trees with butt rot have little or no roots attached when they fall over (Kate Russell)

When most people say “butt” they mean a certain mammalian body part. When botanists and gardeners say “butt” they mean the base of a tree. In either case, butt rot is not something you want.


Butt rot is common in Europe and California but can occur anywhere. This disease is responsible for the complete removal of many orchards. Butt rot kills young trees outright. Removing infected trees is expensive and necessary to prevent the disease from spreading.


Three different bracket or shelf fungi from the Ganoderma genus: G. adspersum, G. brownii, and G. polychromum are responsible for butt rot. Ganoderma root and butt rot (G. applanatum) affect oak trees. All of these fungi devour wood.

Butt rot conk 'Ganoderma brownii' (Tom at Mushroom Observer) CC BY-SA 3.0

Butt rot symptoms

At first, infected trees fail to thrive. Then they decline. Shelf-like conks may grow along the trunk or clefting at graft union. Clefting describes the way the two halves of a graft union peel apart. You may see branch dieback within the canopy, and leaves may be smaller. The rooting of infected trees tends to be shallower than healthy trees. Eventually, the tree will break off at ground level, so keep your distance.
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This disease infects the canopy and trunk, causing both heartwood and sapwood to rot. This makes trees structurally unstable and unsafe to be around. Eventually, branches start breaking off and the tree dies. Before that happens, there are steps you can take to prevent butt rot.

Butt rot conk ‘Ganoderma adspersum’ (Jean-Pol GRANDMONT) CC BY-SA 3.0

Butt rot management

The fungal spores responsible for butt rot are spread on the wind and enter through wounds in the bark. Keeping the bark intact is the best way to prevent butt rot. Keep edgers and mowers at a distance, and remove rubbing branches and unnecessary tree supports. 


As soon as there is a wound, fungal spores can enter. Before you paint over that wound, you need to know that that can cause even more problems by holding moisture against the trunk. If an injury does occur, let the tree heal itself. A callus will form. Hopefully, before pests or pathogens use it as an entrance.


Good drainage is critical. You can improve drainage by mulching and top-dressing around trees with aged compost. Leave at least 8-12” bare ground between tree trunks and any amendments.


Other preventative measures include:

• Leave clean cuts when pruning.
• Prune and train trees for good airflow and structural strength.
• Avoid digging or rototilling around trees.
• Whitewash exposed branches and trunks to prevent sunburn.
• 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, contact a certified arborist. They can inspect the tree for structural integrity and determine the cause and extent of any infection.