Arbutus unedo Dieback help

Hello green thumbs, I am having a problem with my strawberry tree and afraid that I might lose it. It has been more/less happy in this spot for 4 years but now is showing signs of major stress. All the new growth is infested with aphids. The ground is somewhat well draining but we are in Sidney and on top of terrible clay. I’ve sprayed the tree with Sevin to reduce the aphid population. Have put some compost around the base in fear that it’s not absorbing nutrients because of the soil deeper down. It continues to die off and I am not sure what to do!

 

The 'Great Plant Picks' website says: "This versatile shrub tolerates a wide variety of soil conditions including sand and clay, but it must have a well-drained location." Great Plant Picks: Unbeatable Plants for the Maritime Northwest Garden
I would say inadequate drainage is likely at the 'root' of the tree's problem. I'd also be concerned with the very dark band of bark near its base; wondering if that could be a sign of a fungal problem.

 

Thank you for the reply. The dark band is cardboard and sticky stuff to keep pests off. I’ve raised it 2 feet above the surrounding terrain, seemed to work for a few years. I am guessing there is not much I can do about the drainage...