What was the white stuff? Scale? Mealybugs? My Kohala started dropping all of its leaves a while back. About the second time it has done this. I believe my issue is more soil/container related. But I pruned it waaaay back and it rejuvinated the plant. If you are worried it is going to die anyway, I can't see where a harsh pruning will make any more of a negative impact.

Thanks for the advice Ohiojay. I think I'll just have to prune it back and see what happens. How long did yours take to have new growth after the pruning? Here's a couple of pictures of the diseased leaves. Can you tell f it's scale or mealybugs? I do like to grow longans, but it looks like it's more delicate than lychees.

Hard to say. POst your pics and your story on the tropical fruit forum. I know there are several folks growing longan. Maybe they can help out. Mine started to flush pretty quick after pruning.

Is your soil draining fast enough? If you see anything unusual on the bark or in crotches, and you can scratch it off, then it may be scale. Look it up on the web. Post over there first. J

I think I see some scale on the branches and trunk. Not sure though. Your spraying may have killed most of it.
I think I'd pick off all the leaves and dispose of them.
Then spray the entire plant with horticultural oil and wait for new spring growth to show. Then fertilize it.
Meanwhile make sure the roots are firmly surrounded with soil, no air pockets. That's often a cause of stress, and scale etc love stressed plants.
Constantly wet soil would also cause these problems.
As could a tree that's planted deeper than the crown of the rootball. (I don't see that in the picture though)
The recent loss of leaves could be from a couple of cold nights.
Just a few thoughts.

Ohiojay/Treefrog: I snipped off some dead branches and removed all the dead leaves as advised. Now, look at the tree. There are a few places where new leaves are forming. So, there's hope afterall. Thanks so much for all your input.

The only concern I have now is the soil level where the longan is planted. My entire yard goes on a 3 degrees gradual slope from the backyard to the front. The land is also bumpy at some spots. The longan tree happens to be planted on a slightly low spot. I don't know if this will affect the soil drainage or cause it to be constantly wet. I will try to get some horticultural oil to spray on it. Any idea where I could buy it? Will soapy water help with the scales?

You may want to monitor the soil and make sure it does drain well. I don't believe they would do well sitting in water for any length of time. If in doubt, replant to another area and mound it some.