Spirea bushes are generally simple plants to grow as long as the growing conditions and care are ideal. Two common diseases can cause the plant to die off. If you have a spirea bush that is dying, it could be a disease or another reason concerning the region or care.
Bushes with acute verticillium wilt show signs of drying leaves or browning, curling and wilting leaves. Some leaves may show early fall colors and drop from the bush prematurely. Spirea bushes with chronic verticillium wilt show signs of sparse canopy, branch dieback, poor growth and off-colored leaves.
Fire blight causes the branches affected by the disease to appear scorched. If the bush is not pruned to remove the unhealthy branches, the entire bush can die. Removal of dead or dying branches will stop fire blight from spreading to the entire bush. Prune the branch to include at least 12 inches of good branch.
Spirea bushes are hardy in U.S. Department of Agriculture plant hardiness zones 4 to 8. If you live outside of these zones, the bush may suffer from too much heat or too much cold during the harsh winters. If you live in USDA zones 1 to 3, which includes Alaska and International Falls, Minnesota, the cold harsh winter can kill the bush. If you live in USDA zones 9 to 11, the hot summers and not enough cold hours during the mild winters can cause the bush to die.
Bushes need the correct care to grow healthy. Spirea bushes require part sun or shade. The soil condition must have good drainage and a pH of 6.0 to 6.5. Bushes need one application of slow-release granular fertilizer in spring. Use at least 2 inches of mulch around the base of the bush to help retain moisture.