Trident Maple

[Kevalli]

Just noticed this on my Trident Maple and it doesn’t look nice?

 

[RoadManDenDron]

It looks like coral spot to me

 

[WNC Bonsai]

Also check out nectria canker.

Nectria Canker and Dieback

 

[Gabler]

It appears that coral spot is nectria canker.

 

[Kevalli]

Is it treatable ?

 

[WNC Bonsai]

Is it treatable ?

Doesn’t sound good. Here's a RHS link.

Coral spot | RHS Advice

Identify coral spot disease on woody plants and learn how to reduce dieback and maintain plant health.

www.rhs.org.uk

 

[leatherback]

Is it treatable ?

not really. Once this appears you can carve out affected sections, but I have found it hard to really get rid of it.
I have only found this on trees that were already weak, and the disease just spreadds like wildfire.

 

[zita]

if it is around a wound it can be all right.
Severe on the bark like this: get rid of it the sooner the better

 

[vesper818]

Isolate the tree from your others!