The daylily leafminer, Ophiomyia kwansonis Sasakawa, was newly identified in the U.S. last autumn, and growers should be aware that the pest has the potential to spread considerably. This insect, known previously only from Japan and Taiwan, has been confirmed by specimens in Florida, Maryland, Mississippi, Pennsylvania, Tennessee and Virginia. It has also been diagnosed in Alabama, Georgia, Louisiana, North Carolina, New York, South Carolina and Texas. Presence of the pest is evidenced by the unique mining damage in Hemerocallis leaves. The list of confirmations likely will increase with grower awareness.
Damage caused by the daylily leafminer, Ophiomyia kwansonis Sasakawa, is evident on foliage. Larvae feed only on leaves, mining between leaf surfaces and leaving obvious silver tunnels.
Photo courtesy of Sharon Galloway
Possibly the earliest U.S. documentation is an image taken on July 4, 2006, in Kennebunk, Maine (photo, top right). Then, in 2008, damage was first noted by daylily enthusiasts at a national meeting in Texas. Some returned home to find it in their own plantings.
A leafminer fl y rests on a daylily bloom. Although the larvae can cause considerable damage to Hemerocallis foliage, the fl ies do not appear to be harmful.
Photo by V.J. Hickey; courtesy of P. Hickey
The small (up to 5 mm), yellow maggot larvae feed only in leaves of Hemerocallis species and their cultivars, mining up and down as they feed between the leaf surfaces, leaving obvious silver tunnels that persist until leaves senesce or are removed. Multiple generations can create severe foliage disfigurement.
Pupation occurs inside the larval tunnel, usually near the leaf base. The stocky, small (3 mm) black, adult flies often rest on daylily blooms. Although this insect doesn’t appear to kill plants, the leaf damage is of concern for display gardens. Also, as young pale larvae can be virtually invisible in tissue near the plant base, they may escape detection in nurseries when fans are being prepped for sale. At this time, implications for international trade are unknown, as this is a newly emerging pest for U.S. growers.
No chemical controls have been formally tested on this insect. Contact sprays can’t reach the protected larvae; instead, they may kill predators of adults as well as the parasites targeting fly larvae and pupae. Removing and destroying infested leaves may reduce populations. However, daylily leafminer occurs in naturalized daylily stands, allowing reinfestation.
Yellow larva of the daylily leafminer.
Photo courtesy of Gaye Williams
If you see damage in unlisted states, or can recommend effective controls, please contact G.L.Williams at email@example.com. For further information, visit www.npdn.org/webfm_send/1704 and www.daylilies.org/ahs_dictionary/leafminer.html.
Gaye Williams is an entomologist with the Maryland Department of Agriculture, Plant Protection and Weed Management, IPM & Plant Pest Laboratories. She can be reached at WilliaGL@mda.state.md.us