Hi, My Dogwood tree seem to be dying top down. The leader branch did not get leaves this spring and the bottom ones that did are slowly wilting and possibly dying. The tree has two wounds on the trunk oozing waxy substance. I have not seen any borer on the tree. Wondering of its the fungal disease killing my tree and can it be saved at this stage. The tree is young, possibly less than 3 years of age. Its planted in my backyard in a mostly sunny location.
Thank you for contacting the Toronto Master Gardeners about your ailing flowering dogwood (Cornus florida). It’s very difficult to be certain about the cause of these problems without clear close-up pictures of the actual damage. However, based on your description, I think it is more likely that what you are seeing is the result of an insect infestation rather than disease. Specifically, I think that it could be the dogwood borer (Synanthedon scitula) that is hard at work inside your tree where you can’t see it.
Dogwood borer feeds on the inner bark and cambium, just beneath the bark. When the cambium is destroyed, the tree can no longer move water and nutrients up and down the tree between the leaves and the roots, and the tree eventually dies. Infested young trees can be killed in one or two seasons. The larvae of dogwood borer overwinter in the tunnels they have bored and begin feeding again for a short time in the spring before pupating. One of the symptoms of the presence of dogwood borers is crown dieback, which you are seeing.
Dogwood borer must gain access to the tree through wounds or scars or some other opening in the bark. Perhaps the wounds that you have described were the point of entry.
Flowering dogwood is more susceptible to this insect in its first year or two, and when it is stressed. I think stress could be a contributing factor for your tree. While flowering dogwood can tolerate a full sun location, it prefers partial shade, particularly in the afternoon. In its native habitat, it is an understory tree in a woodland setting. It also prefers moist, well-drained soil, so if it is in full sun, it must be kept well watered (but not soggy), especially during periods of drought. Also, I cannot be sure from your picture, but it could be that your tree was planted too deeply, which can also cause stress and eventual death. The trunk flare (where the roots meet the tree) should be visible above the soil line, if the tree is at planted at the proper depth.
Cornus florida is a lovely tree, but unfortunately I don’t think yours can be saved at this point. This link provides information about flowering dogwood that might be helpful as you possibly consider planting this tree again.