Leafminers on Ornamental Plants

Boxwood foliage damaged by boxwood leafminers. Photo: Bruce Watt, University of Maine, Bugwood.org

Updated: October 17, 2024

What are leafminers?

Leafminers are insects that feed inside of leaves between the upper and lower surfaces.
They may be moths, beetles, flies, or sawflies in their juvenile phase (larvae) when they resemble tiny caterpillars.
Their feeding leaves random “mines,” like curving tunnels or blotches, on leaf surfaces. These blemishes are typically lighter in color than a normal leaf but may also appear gray or brown.
Leafminers can be found on a wide variety of shade trees, shrubs, herbaceous perennials, and vegetables.
Most leafminers are a normal part of an ecosystem. Birds and other insects eat leafminers.
A few leafminers are minor pests on garden plants. Most of them cause little damage and control is usually not necessary.

Boxwood leaves damaged by boxwood leafminer. Photo: Bruce Watt, University of Maine, Bugwood.org

On the lower side of a boxwood leaf, a boxwood leafminer larva is visible inside of a "mine" it created. Photo: David L. Clement, UME

Damage from holly leafminer (Phytomyza ilicis). Photo: Daniel Herms, The Ohio State University, Bugwood.org

A typical blotch-type leafmine caused by birch leafminer. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Leafminer trails in the leaves of columbine (Aquilegia sp.). Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Boxwood leafminer (Monarthropalpus flavus) is the most significant insect pest of boxwood in Maryland. The larvae of this fly feed on the tissue between the outer surfaces of the leaves. This feeding results in blotch-shaped mines visible on the underside of boxwood leaves. Visit our page about how to manage common problems of boxwood.

There are several species of leafminers that feed on hollies in Maryland. The most important is the native holly leaf miner, Phytomyza ilicicola, which feeds mainly on American holly.
Severe injury by the native holly leafminer has apparently never been reported in natural stands of American holly, although these insects are found throughout the range of its host. Parasites and other beneficial insects usually control holly leafminers under natural conditions.
Management:
- The simplest way to control the holly leafminer is to pick off and destroy all infested leaves before May. This will eliminate the overwintering insects in the mines.
- Contact insecticides are a less desirable option for controlling holly leafminers because they can kill beneficial insects.

Magnolia serpentine leafminer (native moth): feeds on all Magnolia species, though often observed on sweetbay (Magnolia virginiana).
Birch leafminer (non-native): prefers gray and paper birch; occasionally feeds on black, white, and river birch.
Hawthorn leafminer (native sawfly): feeds on hawthorn (Crataegus spp.).
Locus Leaf Miner (native beetle): feeds on black locust and other members of the Fabaceae (bean) family.
Oak blotch leafminer (native moth): feeds on scrub, post, black, red and white oaks.

The most common leafminers found on herbaceous plants are the larvae of small flies (Agromyzidae spp.). Common examples are the columbine leafminer, serpentine leafminer, and the pea leafminer.
The mining damage may appear as blotches or serpentine or winding trails in the leaves. The female leafminer lays one or more egg(s) in the leaf. Upon hatching, the developing larva feeds on the leaf tissue, creating the mine as it goes. The damage is rarely serious but may be aesthetically unappealing.
Some herbaceous plants that are hosts to leafminers include columbines, goldenrod, perennial sunflowers, daisies, and Veronica.
Management:
- Monitor plants, especially columbine, throughout the growing season. When you noticemines forming, press the area between your fingers to squish the larva or pick off infested leaves and dispose of them.