Fungus growing where large willow branch broke off


I have a willow that had a large branch break off over a year ago. I’ve been spraying with pruning paint but a Large fungus started growing over the summer. Can it be saved? I’ve been told to carve off what I can and spray a mix of Clorox bleach in water. Pictures below.


Thank you for contacting the Toronto Master Gardeners concerning your Willow tree and sending us your photos via our hotmail account.

Trees respond to wounding or injury by forming specialized “callus” tissue around the edges of the wound. Thus, the tree responds to the injury by “compartmentalizing” or isolating the older, injured tissue with the gradual growth of new, healthy tissue. Not only do trees try to close the damaged tissue from the outside, they also make the existing wood surrounding the wound unsuitable for spread of decay organisms. Often a raised area of “callus tissue” will develop in the tree’s attempt to close the wound.

According to the Morton ArboretumOnce a wound occurs, decay-causing fungi can enter the heartwood and the decay process begins. Trees have a unique defense. The wood around the wound begins to produce special compounds in the wood cells that set up a wall or barrier to isolate the infected area. This is called compartmentalization. In a vigorous tree, new growth continues to form and add to the sound wood. Once compartmentalized, discoloration and decay will spread no further unless one of the barriers is broken. Cleaning decayed wood from cavities is not recommended since the compartment wall might be breached and further decay of the trunk could result. Storm-damaged branches should be properly pruned to expedite the healing process. Avoid pruning directly against the trunk since flush cuts can lead to extensive decay. Prune hazardous branches “

In reality, pruning paint may impede healing and encourage the growth of rot organisms and insect infestation. Rather than seal out infection, wound dressings often seal in moisture and decay. In most cases, it is best to simply let wounds seal on their own. The presence of fungal growth indicates that fungal spores have already entered the wound.

I would advise against utilizing a dilution of Chlorox; instead I would seek the expert opinion of a certified arborist as soon as possible.  An arborist will be able to assess your tree in person and determine the full extent of damage.  He or she will also be able to give an accurate prognosis and inform you of any possible strategies, if any, to help save the tree. To find a certified arborist in your area, please consult the ISA Ontario website.

You may wish to read the following articles for additional information:

Should I cover large pruning wounds with a tree wound dressing?

The Myth of Wound Dressing