- There are over twenty species of holly native to the United States. Most of these species are limited to the Southeast Coastal Plain and many are grown in Maryland.
- Leaf miners attack several kinds of holly and the value of these plants has in some cases has been greatly reduced.
- In Maryland, there are several species of leaf miners which feed on holly. The most important is the native holly leaf miner, Phytomyza ilicicola, which feeds mainly on American holly.
Life cycle and damage
- Holly leaf miners adults are small flies.
- There are two species of leaf miners that feed on holly: native holly leaf miner (Phytomyza ilicicola) feeds mainly on American holly and the holly leaf miner (Phytomyza ilicis) a European species.
- Severe injury by the native holly leaf miner 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 the insect under natural conditions.
- Damage is due mainly to the feeding of the minute yellow fly maggots. They feed by mining between the top and bottom surfaces of the leaves.
- The mines begin as narrow, inconspicuous tunnels. By fall, the mines look like irregular dark streaks.
- Adult females also cause injury by inserting their ovipositors into the leaves. Males and females feed on the juices that appear from the punctures.
- A large number of punctures in a leaf may cause a leaf to become stunted and twisted.
Management of holly leaf miners
- When possible American hollies should be grown in partial shade. Trees in full sun usually suffer more damage by this pest.
- The simplest way to control the holly leafminer is to pick off and destroy all infested leaves before May. This will eliminate the overwintering maggots in the mines.
- Where the size and/or number of plants makes this method impractical, this pest can be controlled by timing an insecticide spray with the emergence of the adult flies. This tends to be in mid-May.