The idea behind these treatments was that an open wound was vulnerable and that we could ‘help’ our trees by painting the cut surface with tar, asphalt, wound paint, or some other sealant. Instead of providing protection, these treatments actually seal in harmful bacteria and fungi, increasing the chance of disease or decay. Also, there are certain disease-carrying organisms that love to feed on or are otherwise attracted to the sealant!
It ends up, trees already know how to protect themselves. Just as our skin forms a callus in response to hard work and friction, trees create tissue over wounds to protect themselves from pests and diseases. The word ‘callus’ is from the late Middle English Latin word ‘callosus’ which means ‘hard-skinned’. Trees are able to generate their own ‘hard skin’ to cover a wound. If that process is interrupted with oil-based sealants, the internal processes of decay prevention may also be interrupted.
An exception to the rule
One case where wound dressing is a good idea is in regions (like ours) where oak wilt is a problem. If an oak in these areas is damaged or requires pruning, a sealant that contains insecticide and fungicide can prevent loss of the tree.
You can grow a surprising amount of food in your own yard. Ask me how!
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