They are susceptible to many plant diseases and are fussy about where they like to grow. The first you can't control, but the second one you can. Let's start with what can be controlled.
Roses prefer a planting site with good drainage and ventilation.
Avoid shady spots and dense plantings. Good air circulation helps the leaf surfaces dry faster, which helps prevent disease. Roses also need to be fertilized on a regular basis. Apply fertilizer specific to roses, which is available at full-service garden centers. What gardeners can't control is the weather.