Purpleleaf sand cherry bushes have beautiful, fragrant, long-lasting blooms, but they are not very hardy plants. In fact, most have relatively "short service life spans," according to the Ohio State University Extension due to "significant disease and pest problems." The best way to keep your purpleleaf sand cherry alive and well for as long as possible is to be able to spot problem signs early on, so that you can treat the plant before it is too late.
Powdery mildew is usually a product of a humid, shady environment around the plant. Powdery mildew can be black, gray, white or pink, and it looks like a heavy dusting of chalk on the leaves and branches of the shrub. Left unchecked, it can weaken the bush and leave it vulnerable to other infections that can kill the purpleleaf sand cherry. However, if you remove affected portions of the plant using sterile pruning and rake away plant debris underneath the shrub, then you can likely control the infection and save the bush.
Verticillium wilt is a serious disease that causes the purpleleaf sand cherry's leaves to crumple, turn yellow and wilt before falling off the tree. As the disease progresses, entire branches or portions of the shrub may die back. If you scrape away the bark, infected parts of the shrub will be stained olive green. Remove all affected portions of the plant by using sterile pruning methods, and dispose of the debris in sealed bags or by burning. Fertilize the plant with a fertilizer low in nitrogen and high in potassium. If symptoms return, remove as much of the plant as possible, leaving the roots intact to the greatest degree possible to prevent further spread of the disease.
There are several forms of wood rot that can attack the purpleleaf sand cherry shrub. Shelf fungus, which forms seashell-shaped shelves on the sides of the main stems of the shrub, can work away at the woody portions of the plant until it kills the entire cherry bush. Other forms of rot develop cankers that girdle the stems, resulting in defoliation and death. You can treat these infections with a fungicide or remove them by using sterile pruning techniques. Cut them during cold weather when the infection is less likely to spread.