Daylily leaf miner damage has been observed both in the landscape and at plant nurseries in Western Massachusetts this summer. Native to Japan and Taiwan, the first sighting of this insect pest in the USA is believed to have occurred in Maine in 2006. By 2014, it had been identified in 26 states from Maine to Texas.
Adult lily leaf miners are small black flies with red eyes and wide, clear wings. They may be seen resting on leaves or flowers. Adult females lay eggs within the leaves. The larvae hatch and proceed to eat their way through the leaf tissue, creating silvery-white lines on the foliage. Larvae change from off-white to bright yellow as they mature, grow to about 5mm (0.2 inches) in length, and are sometimes visible inside of their mines. Pupae may be found anywhere within the leaf tissue during the growing season, but in the fall they are usually located near the crown of the plant, where they overwinter. Pupae are slightly smaller than larvae and light brown in color. In the Northeast there may be 2-3 generations per year.
Fortunately, the daylily leaf miner is highly host specific- it infests only Hemerocallis species. This is good news for Asiatic lilies (Lilium species), which are having a hard enough time as it is with the lily leaf beetle. Also fortunate is the fact that the damage caused by daylily leaf miners is largely aesthetic and the level of plant injury is typically minor. Remove infested leaves and plant debris and dispose of them in the trash. Examine plants carefully and do not sell or purchase plants on which leaf mines are observed. Contact insecticides will not be effective against eggs, larvae, or pupae. No biological control agents have yet been identified.
Report by Angela Madeiras