The leaves of my 20 year old Japanese maple are curling up, and on one branch they are dried out completely. On other leaves there is speckling.
Do you know what causes this, is it worrisome, and Is there anything I can do to help?
Thank you for contacting the Toronto Master Gardeners with your concern for your Japanese maple.
The most likely cause is a fungal born disease called verticulum wilt, which tends to start by first yellowing or wilting of individual limbs or portions of the canopy (often referred to as “flagging”, and is very indicative of your photograph). This disease usually appears in mid-summer, frequently after periods of hot, dry weather. killing individual branches or section of a tree, before expanding to other sections of the tree.
Infected trees die slowly or suddenly, depending upon the extent of infection and the overall health of the tree. Trees weakened by drought or root damage are thought to be more prone to disease.
There are no chemical controls for this disease of maple once trees are infected. However, efforts to maintain tree health and vigor can help to prolong the life of the tree. It is helpful to prune affected limbs as soon
as symptoms are evident.
Tools should be thoroughly disinfested between cuts with a 10% solution of household bleach or 70%
alcohol. Additional efforts to promote tree vigor by watering, fertilizing (only as necessary, based on a soil test) and avoiding other types of stress are helpful.
Since the fungus is soil-borne, when the time comes to replace the tree, it is necessary to avoid planting susceptible species in the area.
While this is the most likely diagnosis from the photograph, it should be noted that the photograph is a bit limited in scope, and it is possible that this can also be other pests such as aphids, spider mites, less likely anthronose or even scorching. Careful observation of the curled leaves should revel if you have infestation of aphids or even spider mites, just to discount those. If you suspect that your tree has not been getting any irrigation and may be dry and scorched, then irrigation of the tree would be in order. Having stated this, the best match from the photograph is unfortunately verticulum wilt.