Tree diseases are conditions that affect the health and growth of trees, often caused by pathogens such as fungi, bacteria, and viruses. These diseases can lead to symptoms like leaf discoloration, wilting, and premature leaf drop. Some common tree diseases include Dutch elm disease, oak wilt, and powdery mildew. Preventing tree diseases involves proper care, including regular watering, pruning, and monitoring for signs of infection. Healthy trees are more resistant to diseases, so maintaining good soil quality and avoiding overcrowding can help. If a tree is infected, treatments may include removing affected branches or applying fungicides to control the spread.