The answer to 'why is my shrub disease' is that your shrub may be suffering from a fungal, bacterial, or viral infection. Common symptoms include discolored, wilting, or dying leaves and branches, as well as visible signs of fungus or pests. The cause could be environmental factors like poor drainage, overcrowding, or improper pruning, or it could be a pathogen that has infected the plant.
If you notice any signs of disease, it's important to diagnose the issue quickly and take appropriate action. In many cases, you may be able to treat the shrub yourself with fungicides, pruning, or adjusting the growing conditions. However, for more serious or persistent problems, it's best to consult a professional landscaper or horticulturist who can properly identify the issue and recommend the most effective treatment.