Astilbe Leaves Turning Brown

I have a dozen astilbe plants that all look like they're been burned from the inside of the plant out. Is this a fungus or a bug? These plants are four-years-old and until this summer have looked great.

A lack of water can cause the symptoms you described. Astilbes need moist soils and perform best in partial to full shade. Continue to water as needed throughout the fall. I have seen drought stressed astilbes return the following season. Continued drought stress will kill the plants. Next year keep the soil moist, not soggy and mulch. Apply a layer of shredded leaves, evergreen needles or other organic mulch to the soil surface to keep the roots cool and moist.