Buttonwood turning yellow

I have a buttonwood, with lots of deadwood, that has been doing wonderfully until now. Leaves have started turning yellow and dropping off. I don't see any sign of an infestation and I know you can't water them too much. Does anyone have any experience with this issue? I've had the tree for three years and it was repotted about 15 months ago. I have always fed it with MiracleGro. It is in full sun until 2:00pm and sits in dappled light after that. Any advice would be greatly appreciated.

Thanks
Jane

Here is a care guide:
http://www.bonsaimary.com/buttonwood-bonsai-care.html

What kind of soil is it in? It sounds like it might be getting overwatered, but I don't have any experience with buttonwoods.

Buttonwood can tolerate wet feet...they can live near marshes and mangroves.

Mine loves lots of sun. I am in TX and it is out in full sun the whole day. Only reason I get yellowing leaves is when it is scale infested and or when the old leaves are getting replaced.

I've read they do not like being sprayed with anything oily...check that you did not do this. Good luck!

Thank you Kennedy and Dario, for you comments. This buttonwood is in very gritty bonsai soil with almost no pine bark at all. It lives in full sun all day and gets watered once or twice a day as needed. At this point I believe that it has some kind of fungus as the nebari has turned black. I will be very careful not to use an oil based spray on it. It has new leaves, albeit at the tip of very long branches so I expect it will be OK after I spray it and give it a trim. After I get it back into shape I'll post a pic.

Thanks,
Jane

Jane,

Check this. https://ibonsaiclub.forumotion.com/t15916-buttonwood#161572

My soil mix for this is highly organic...but I am in TX so it might not work as well for you. Just thought I'd mention it.