are some spirea more likely to get diseases than others?
I don't know what exact kind they were (not magic carpet or gold mound) but they were installed the summer before they all (20-30 plants) died. I don't think it was water issues. they were on the north west side of a building partial to full sun. this year the same type of mass die off is happening on the east side of the same building with the same type of spirea. It looks like a disease to me but i don't know much about plant diseases. I want to replant with magic carpet spirea but i don't want to have another die off.
It looks like the spirea have one of several leaf spot diseases known to affect spirea. You may be able to control the disease by spraying with Daconil. Since these fungi can over-winter in dropped leaves, it is important to clean up all fallen debris at the end of the season. Over-head watering is a risk factor for leaf spot diseases; a low-pressure soaker hose or drip irrigation is recommended. I would not immediately replant the same genus where there has been a disease problem. If this is done, keep a close eye for early symptoms of leaf spot and treat with an anti-fungal spray immediately. Repeat as necessary until any spores that spent the winter in the soil are gone. Of course, correct the over-head watering if this is the current practice.