Butt Rot

Butt rot? Really?


Yes, Virginia, there is a fungal disease of almond trees called butt rot. Is 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 use the word “butt” they are talking about 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 very common in Europe and California. This disease is responsible for many orchards having to be removed completely. Butt rot kills young trees outright and infected mature trees must be removed to prevent the disease from spreading.


Butt rot is caused by three different bracket or shelf fungi from the Ganoderma genus: G. adspersum, G. brownii, and G. polychromum. Another type of Ganoderma root and butt rot, caused by G. applanatum, attacks 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 simply fail to thrive. Then they decline. You may see shelf-like conks grow along the trunk or clefting at the 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 than those of healthy trees. The rooting of infected trees tends to be more shallow than normal. Eventually, the tree will break off at ground level, so keep your distance.


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

Butt rot is spread by airborne spores that enter through wounds in the bark, so the most important way to prevent butt rot is to protect your tree’s bark. Keep edgers and mowers at a distance. 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. Better to not injure the tree in the first place. If a wound occurs, let the tree heal itself. A callus will form. Hopefully, before pests or disease use it as an entrance.


Good drainage is also important. You can improve drainage with mulch and by top dressing around trees with aged compost, just make sure nothing is touching the trunk. It’s a good rule of thumb to leave at least 8-12” of bare ground between tree trunks and mulch.


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
•  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 contact a certified arborist. They can inspect the tree for structural integrity and determine the cause and extent of any infection.