My tree, she is sick

I planted 8 trees in the garden at the start of the year and 7 of them are thriving with an average of about 8 inches of new growth atop them,the other one is starting to wilt and has light blue spots all down it, especially on the uppermost leaves. I took a closer look today and noticed a few blue flies on it, I have no idea what they are.

How can I heal my tree?

I'll post pictures if needed. Thanks a lot.

 

I've been out and taken some pictures. Here is a picture of the leaves up close so you can see the damage:


And here's a picture of one of the little bugs that are on it, perhaps you can identify them:


You only have to compare the healthy plant to the sick one to see something is wrong



Oh, and they're "bird cherry" trees, also known as Prunus Padus according to WikiPedia.
I've had a look and noticed the bugs on a plant nearby, so they're obviously spreading.

 

I'm unfamiliar, but are the bugs on the tree aphids? If so I'm sure I could get a spray or something to make them go away.

 

They are Aphids, give them a blast with Provado.

 

Thanks a lot for your help. You know I have never heard of grease bands until now. I'll look them up some more when I don't have work to do and maybe even try to make my own if they're simple enough.
I have a friend who owns a garden centre I'll maybe ask him next time I'm there. In the meantime I might pick up all the ladybirds I see around the garden and drop them onto the tree, then hope they take the hint.

 

I bought some bug spray yesterday and gave the plant a good spray once the sun went down. Now, having been out all day, I've just checked on the tree and the leaves have gone brown, is that a bad sign? Is it on its way out?