Oriental lilies are tall architectural plants with large showy flowers that bloom in late summer. The fragrant flowers are white, pink or red, and sometimes streaked with contrasting colors. They grow best in full sun or partial shade, and need very well-drained soil and good air circulation. The diseases that affect Oriental lilies are caused by poor drainage or damp air.
Botrytis blight is a fungal disease that begins on the lower leaves of Oriental lilies and moves up the stems to the flowers. Infected leaves develop reddish brown spots, some of which grow a fuzz of gray mold. Infected flowers decay and grow gray mold before falling off. Remove and destroy diseased plant parts to prevent the spread of botrytis blight.
Various fungal rots can infect the bulbs, roots or stems of Oriental lilies. Symptoms include foliage that turns yellow and wilts, foliage that turns brown on the edges and between the veins, plants that grow slowly or emerge late and plants that die. If the symptoms are mild, a fungicidal spray approved for Oriental lilies applied according to the manufacturer’s directions may stop the disease. In severe cases, the plants should be removed and destroyed.
Lily mosaic is a viral disease of Oriental lilies that is usually spread by aphids. The foliage will be flecked, mottled or streaked with necrotic tissue. The plants grow stunted and produce abnormal flowers. A pesticide approved for aphids on Oriental lilies can be applied following the manufacturer’s instructions to control the insects. If the plants are severely infected, remove and destroy them.