The answer to 'shrub yellowing' is that there are several common causes, including nutrient deficiencies, overwatering, disease, or pests. Symptoms can include leaves turning yellow, wilting, or dropping prematurely. Solutions depend on the underlying cause, but may involve adjusting soil, watering, or treating with fertilizers or pesticides.
If the yellowing is widespread or the shrub is not recovering, it's best to consult a professional landscaper or arborist to properly diagnose and treat the issue. They can assess the plant's health, identify the problem, and recommend the most effective course of action.