The answer to 'why is my garden disease' is that there are several common causes of garden diseases, including fungal infections, bacterial infections, and pest infestations. Symptoms can include wilting, discoloration, and rotting of plants. Solutions may involve using fungicides, removing affected plants, and implementing preventative measures like proper watering and air circulation.
If the problem persists or you're unsure of the cause, it's best to consult a professional landscaper or horticulturist. They can diagnose the issue and recommend the most effective treatment.