I have a white serrissa tree which I was given for my birthday over 10 years ago. It has always been a healthy tree and I have never had any problems with it. Just before Christmas one of my other trees lost a lot of leaves. They seemed to shrivel up and fall within a few days. I could not see anything on the leaves but there was a sticky film on the leaves which I think may be caused by wooly aphids. There were what appeared to be insect casts around the tree.

I sprayed all 3 of my trees with Provado bug killer after speaking to someone at the local garden centre.

The original tree has been fine since. The serrissa however a couple of weeks later dropped all it's leaves and has been struggling ever sincce. It seems to put out new leaves then within a week they go black at the tips then shrivel up and die. I have sprayed it with the insecticide a few times but the leaves keep being attacked. I can't see any visible signs of any pests even using a magnifying glass. There is no sticky residue like the other tree had, they just seem to shrivel and die.

I'm trying not to over water the tree as it obviously isn't growing very well. The trees sit on a south facing window in the kitchen and are all over 10 years old.

What can be attacking my tree and how do I get rid of it?

Thanks for your help

Sharon