I live in mid-town Toronto and have an ailing 30 year old Japanese Maple. It is a lovely 30 foot plus tree, and it has added to the beauty and charm of my home. However, in the last while I have noticed that the leaves started to shrivel, some downwards and many in a cocoon shape. I also noticed that the tree produced an abundance of seeds, which I thought was a positive sign.
My adjacent neighbour recently installed artificial turf and my tree is growing right at the property line. Also, a nearby Forsythia has been totally defoliated by spider mites, and upon closer inspection of the leaves of my Japanese Maple I discovered that there are signs of mite infestation, including webbing inside the shriveled leaves.
Most recently, to our dismay we have just found a diseased branch which was hanging over our neighbour’s garden (see photo). We sterilized a saw and cut it off, the remainder of the branch seems to be in good shape. Is this Verticillium wilt? We are still fighting the Spider Mites but surely they could not cause such damage?
I think there are a number of factors that are affecting your poor Japanese Maple. To begin, we have had a very hot and dry summer with long periods without rain and unless you have been irrigating your garden and trees regularly, chances are they have been stressed making them more susceptible to ailments. The dry shrivelled leaves could have been simply leaf scorch due to this dehydration; however you also mentioned the cocooning shape and webbing inside the leaves which sounds indeed like the mite infestation also affecting your Forsythia.
Your neighbour’s installation of artificial turf so close to your tree would have definitely had an impact on the root system.
The most recent photo of the affected branch you have removed could indicate your tree has Verticillium wilt. The wood under the bark of wilting branches is typically discolored in streaks of green to black in maples. With this disease, often the foliage on only one side of a tree wilts. Have you noticed this to be the case? It might be difficult to determine this due to the mite infestation. The fact that your tree produced a lot of seeds can also be a symptom of this disease.
To help your tree, use a soaker hose at its base and create a watering ‘moat’ to concentrate moisture at the drip line. Continue pruning out any badly affected branches taking care to sterilize pruners between cuts. Dispose thoroughly of all debris off site and consider removing and disposing of the badly affected Forsythia.
To know with certainty if your tree does indeed have Verticillium wilt you would have to have your soil tested.
Here are suggested sites to visit for more information on Verticillium wilt and Japanese maples. The link to spider mites aims specifically at fruit growers, but may be of some assistance: