Yellowing and falling leaves on a daphne plant can indicate various issues. Overwatering or poorly draining soil can lead to root rot, causing leaf discoloration. Insufficient sunlight or excessive heat can also stress the plant, resulting in yellowing leaves. Additionally, nutrient deficiencies, such as iron or magnesium, can cause leaf yellowing. Pests, such as aphids or spider mites, could be feeding on the leaves, causing damage. It is important to assess the growing conditions, address any potential problems, and provide appropriate care to help restore the health of the daphne plant.