Q.rose of sharon trees are dying
My established rose of sharon trees are wilting and dying even with water–in a week they are gone. Why? What could cause this?

Rose of Sharon can be effected by some pests and the fungus, Botrytis.
Inspect your plant for any other signs or evidence of disease.
Excess moisture could cause root rot.
https://www.gardeningknowhow.com/ornamental/shrubs/rose-of-sharon/rose-of-sharon-bush.htm
http://extension.illinois.edu/hortanswers/plantdetail.cfm?PlantID=400&PlantTypeID=8