My smoke tree seems to be dying. The leaves are turning brown. Last year at the end of the season the leaves turned brown but did not actually fall off.
Thank you for contacting the Toronto Master Gardeners concerning your Smoke tree, Cotinus obovatus.
It is difficult to say why the leaves of your smoke tree have been turning brown. My first thought would be that the leaves are drying up due to premature leaf drop. During the month of August and September we have had significantly little rainfall accompanied with extremely hot sunny days. Unless, you have been giving the tree additional water it could be that the tree is naturally losing leaves to protect itself from water loss through leaf transpiration.
Smoke trees are known to have a high tolerance for drought. Usually normal rainfall should be enough for the tree except in prolonged periods of drought, which is what we have seen in the month of August. I would begin by giving the tree a thorough soaking. I would also suggest adding 3-4” of mulch around the roots of the tree making sure to keep the much away from the tree trunk, since this promotes fungal diseases and rot. The mulch helps keep the roots cool in hot summer weather, helps retain moisture and insults the roots in the winter.
That being said, there are a number of diseases that can affect the Smoke tree-:
Verticillium Wilt: Leaves will appear to wilt and turn yellow around the edges. This soil-borne fungal disease blocks the water-conducting cells in the tree causing the leaves to wilt due to lack of water. This may eventually kill the tree. There is no cure for this disease. The only course of action is to prune away infected areas and clear away any fallen leaves and other plant debris from around the tree. Dispose of the infected material, do not place it in the compost bin
Leaf Spot Diseases: Leaf spots are caused by fungal infections and rarely are a danger to healthy trees. Leaf spots can vsry in size and colour. Fungal spores spread by splashing waterso avoid overhead watering and prune the tree to improve air circulation around the tree so that the leaves dry out quicker after a rainfall.
This article gives additional information on possible Smoke tree problems. We also have numerous archived posts on Smoke tree.
There are many previous answers in our library that discuss the smoke bush and pruning. I am including a few below for you to reference.
Good Luck with your Smoke tree.