NC State Extension Publications

Description and Biology

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The daylily leafminer, Ophiomyia kwansonis, is a relatively new pest to North Carolina. This tiny, pale yellow maggot grows up to 3/16 inch long. With a handlens, it may be possible to see a black structure inside the head and two prominent black knobs (spiracles) on the thorax. The pupa is shorter and orange to brown with black spiracles on the thorax and rear. Daylily leafminer adults are tiny (about 3/32 inch long), black flies with dark red eyes and clear wings. Females insert eggs into the lower leaf surfaces usually one per leaf and usually near the tip. Tiny maggots hatch and mine downward more or less parallel to the midrib. However with severe infestations of two or three or more maggots per leaf, the mines may zigzag, circle, or crisscross. We have at least three generations per year.

Daylily leafminer

Daylily leafminers typically mine downward.

Daylily leafminer pupae

Daylily leafminer pupae resemble tiny seeds inside the larval mine.

Daylily leafminer flies

Daylily leafminer flies are very small and dark.

Host Plant

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Daylily is the only host plant known for the daylily leafminer. Pale lines on the leaves are the first sign of daylily leafminers. The larva usually mines downward parallel to the midrib and pupates toward the base of the leaf. Infested leaves become unthrifty and may wither and remain disfigured for the whole growing season

Daylily leafminer mine

Daylily leafminer mines are clearly visible through the leaf surface.

A heavily infested daylily.

A heavily infested daylily.

Residential Recommendations

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The daylily leafminer is primarily a nuisance pest of daylilies. Except perhaps with extreme infestations, this pest does little actual harm to the health of infested plants. Leafminers in general are plagued with tiny parasitic wasps. After the initial alarm of discovering daylily leafminers in the landscape, if one can refrain from applying an insecticide, the population will probably die away gradually. Systemic insecticides such as imidacloprid can be applied to the leaves or soil beneath infested daylilies to control daylily leafminers (however, damaged leaves will not improve in appearance after treatment). One problem with using imidacloprid is that spider mites may suddenly flair up, so keep an eye on treated plants to prevent spider mites from causing even worse damage.

Other Resources

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For assistance with a specific problem, contact your local Cooperative Extension Center.

This Factsheet has not been peer reviewed.

Author

Professor Emeritus
Entomology & Plant Pathology

Publication date: Dec. 1, 2018
Revised: Sept. 13, 2019

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