Q.purple sandcherry has yellow leaves
My Purple Sandcherry bush is about 10 yrs old and this July the leaves have turned yellow brown throughout. What caused this and is there anything I can do? It flowered and did well until mid July. Always prune it and fertilize.

Yellowing leaves are generally an indicator of watering issues. To little or to much.
If the area is dry, I would add some additional water. 2 to 3 inches of hardwood mulch can help with moisture retention.
Also check for insects or fungus issues. Neem Oil is a good treatment for either as it works as both an insecticide and fungicide.
https://www.gardeningknowhow.com/ornamental/trees/sand-cherry/purple-leaf-sandcherry-info.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm