Acer problem

I recently bought and planted a beautiful coral bark acer. When I planted it, it was about 2m tall, but I am not sure how old it is. For the first 4-6 Ieks it did really Ill but recently I have noticed some problems. I first noticed that the leaves on some branches Ire turning yellow and then all dying, but not dropping off. On closer inspection I noticed some spider Ibs on the plant and some tiny red spider looking insects. I also noticed some black patches on the tree branches (see photos), and it appeared to be in the area of these black patches that the leaves and branches Ire dying. Some parts of the plant look fine, but it is not thriving and I cannot spot any new growth coming through. It is planted in an area with dappled shade and plants in the same area (lupins, iris, japonicas) are all doing Ill. Any thoughts or suggestions about what the problem might be or how I can fix it would be greatly appreciated!

Iâ??ve posted pics of the problem here http://www.flickr.com/photos/12669270@N02/sets/72157624183426204/

 

Hard to say for sure, I rather suspect it requires much more intense watering. A acer that is 2 metres high is quite a mature tree and will require a great deal at first. Although we have had a very cold winter the Spring has been very dry.

I wouldn't personally use one but a pesticide can deal with the infestation-although I do think it is probably weakened from dry conditions which does in turn make it susceptible to any problems.