I have several Katsura Japanese maples, some of which I rooted and the mother plant. All the smaller rooted ones wilted off and died and now I notice the leaves on the mother plant are also blackening off, shriveling etc. Whole branches are dead. What do I do? I am removing the dead stuff but I could apply an anti-fungal if necessary. My concern is that I have many other Japanese maples in the yard which have not been affected at this point but I do not want it to spread. Suggestions?
Thank you for contacting the Toronto Master Gardeners.
It sounds as if your Japanese maples are suffering from Verticillium wilt.
Verticillium wilt is a fungal disease caused by soil-borne pathogens Verticillium dahliae and V. albo-atrum. This fungus enters the cambium layer of the plant through the roots or injured areas on the trunk and blocks the flow of nutrients within the tissues. This leads to dryness and wilting in affected twigs. There will be brown streaking in the sapwood under the bark and in cross section, an infected branch will show a dark ring or pin-point dark spots. There is no cure for this disease – spraying anti-fungal chemicals will not work.
Verticillium wilt is difficult to control because it persists in the soil indefinitely. Integrated pest management strategies to try are: 1) prune damaged areas. Maybe this pruning in addition to increasing the vigor of the tree through consistent watering and mulching to maintain soil moisture and moderate soil temperatures will help to keep symptoms in check.
The disease can be transmitted on pruning tools. Be sure to sterilize pruners with a 10% solution of household bleach between cuts and avoid moving soil or debris from an area of known infection 2) plant resistant or tolerant species in this location. This link has lists of plants that are vulnerable to this fungus and lists of plants that are immune to verticillium wilt
For more information on Verticillium wilt, click here.