In many areas daylilies are in bloom or bud. Recent news of the presence of the daylily leaf miner should have both home and commercial growers on the lookout for this pest. 

From Plant Health as reported in “American Nurseryman” magazine:

“The daylily leafminer, Ophiomyia kwansonis Sasakawa, was newly identified in the U.S. last autumn. This insect, known previously only from Japan and Taiwan, has been confirmed by specimens in Florida, Maryland, Mississippi, Pennsylvania, Tennessee and Virginia, and 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. Possibly the earliest U.S. documentation is an image taken on July 4, 2006, in Kennebunk, Maine 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.

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.

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. 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.

If you see damage in unlisted states, or can recommend effective controls, please contact G.L.Williams at williagl@mda.state.md.us. For further information, visit http://www.npdn.org/webfm_send/1704 and http://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.”

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