I have a smoke tree in my small back yard. It’s about 20 years old. This spring I notice many black growths on branches (see picture). The tree is in a corner that is shaded, although the tree stretches up to the sun. Two close by trees (French Lilac and Locust) are healthy.
Can you tell me what this growth is and what to do about it.
We believe this is Black Knot, a fungal disease that affects woody stems with growths such as your photograph shows. These growths or knots disrupt the flow of nutrients and water through the tree, and can cause dieback of branches. This disease is often described as affecting mostly members of the Prunus family – particularly plum and cherry trees – and although it has many host trees, some tree species are not affected, which is why your nearby trees remain healthy. Spores are spread in the warm spring weather, so now is the time to manage this, before our weather turns warmer.
The best approach to dealing with this fungal disease is to cut off all affected branches, making sure that your pruning equipment is sterilized between each cut. Do not compost the branches you remove – they should be disposed of or burned to prevent spread of the disease.
This website provides an overview of this disease and its management options: https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/fungal-spots/black-knot.aspx
If you feel this is too much for you to attempt, you might consider calling in an arborist who will be able to prune effectively, and can advise you on the health of your smoke tree. Landscape Ontario provides a listing of arborists: https://landscapeontario.com/search?lat=43.653226&lng=-79.3831843&query=Arborists%2FTree+Care