Do you have any idea what it is?
This could be a fungus or even insects.
Treat with Neem Oil as this works as both an insecticide and fungicide.
Here are a few links for you with more information.
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
I cut my four, sad, old sand cherries down to about 8 inches. Some of the shoots are coming from the cut off trunks. Some are coming out of the ground around the plants. Should I select some to prune? Which ones? Should I trust the roots? Or dig them out and start anew?
You could propagate the root cutting. I would allow it to come back from the original root system.
If your not happy with the growth and plant as the season progresses, fall is always a great time to make some new planting decisions.
Here is a link with more information.
https://www.gardeningknowhow.com/ornamental/trees/sand-cherry/purple-leaf-sandcherry-info.htm
Are the fruit of the purpleleaf sandcherry safe to eat? (The large cherry fruit is a delight to pick).
According to the following article, the fruit is edible but is usually made into jellies and other confections first. It may not be so tasty straight from the tree.
http://www-pub.naz.edu/~treewalk/north_tree_walk/prunuscistena/
I have a tree that bears a large dark red cherry, and am not sure of its species/care. It's getting some quite extensive branch growth, and I'd like to prune it. How and when should this be done?
Spring is the best time to prune a Purple Leaf Sandcherry.
Here is a link with more information.
https://www.gardeningknowhow.com/ornamental/trees/sand-cherry/pruning-plum-leaf-sand-cherry.htm
What precautions should I take for the winter when it comes to the purpleleaf sand cherry? Should it be covered or protected for the winter?
Purpleleaf sand cherry is hardy in zones 3b to 7b, so with an established tree in those zones, it won't need protection. In colder zones or during the tree's first winter, it can benefit from protection:
https://www.gardeningknowhow.com/garden-how-to/info/wrapping-plants-in-burlap.htm
http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/protecting-from-winter-damage/
My sand cherry bush started to bud and then we had a nasty frost and now it's not blooming or growing leaves at all when it should be full by now. Does this mean it is dead or dying or just dorment? Will it recover next year?
If the flower buds were killed by frost and cold, you will not have flowers this season.
The good news is the foliage is just as pretty on a Sand Cherry and hopefully Mother Nature will relax and your shrub will bloom next year.
This link has more care information.
https://www.gardeningknowhow.com/ornamental/trees/sand-cherry/purple-leaf-sandcherry-info.htm
I just had a Plum sandcherry shrub planted by a Garden Center 10 days ago. I noticed that overnight about 1/4th of its leaves were on the ground. I shook the shrub and more leaves fell off. I'm sure if I shook it even more all of the leaves would drop off. Why is this happening and should I be concerned? Ed Turk capstoneec@wowway.com
Check the soil; is the soil wet and poorly draining?
Is the soil dry; though they can be drought tolerant if established, it may need some watering.
Pests and disease could also cause leaf drop. Check for signs of pest on the the leaves and check the bark for signs of disease.
Treat pests with Neem Oil.
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