Please can you help? I woke up this morning and my two beautiful Alder trees seem to be leaching a type of what looks like oil (or maybe sap). The tree trunks have gone black from the roots half way up the trunks. When I touch the trunks it almost looks and feels like it has been sprayed with oil? Its spring in New Zealand now and I noticed the leaves on the trees are small. I have heard of trees which run sap when under stress but I thought sap was sticky this is like an oil and has a sweet smell not unlike Pine Oil. I am upset as we have fought our neighbours in court to keep these trees I am just hoping they have not been over and sprayed some type of oil on the trunks. Surely not. If you can help at least by identifying is sap a type of oil it would help me. Many Thanks Rosemary Riddle.
An Alder Tree
Certified GKH Gardening Expert
The sap of some trees is darker and can appear oily. Common reasons for trees to leak sap are physical injury, bacterial or fungal diseases, environmental stress, or insect damage. If you don't see any physical injuries on the trees, check for symptoms of bacterial disease:
One form of bacterial disease affecting alders in New Zealand is below:
If the problem persists, you may want to consult an arborist or university extension service professional to help with diagnosis and treatment.