Landscape and Nursery - Some Leafminers to Look For

The following is information on some leafminers that may be active in the landscape now or in the near future.

Birch Leafminer and Hawthorn Leafminer

Common lilac is in bloom and this is the time that we generally see birch leafminer and hawthorn leafminer adult activity. The insects overwintered as pupae. The adults will be searching foliage and females will oviposit into foliage over the next couple of weeks. The eggs are laid through slits in the foliage. Your customers will see blotch mines form in the foliage in June. There are 3 - 4 generations per year.

Control: European birch is most susceptible to birch leafminer. Paper birch and gray birch are also susceptible. River birch can have the foliage damaged but it is usually a few leaves and the damage is very tolerable. Systemics such as imidacloprid and dinotefuran can be applied to the soil of susceptible trees to protect foliage.

Holly Leafminers

American hollies are about 10 –14 days away from flowering. Adult holly leafminers emerge just about the time of flowering of American holly. Adults are gray to black colored flies. The adults are out for several days before they mate and females start laying eggs.

Control: Soil applications of imidacloprid (Merit in Landscape and Marathon in Nursery), thiamexthoxam (Flagship) applied as a soil drench or dinotefuran (Safari) applied as soil application gives very effective control.

Reprinted from the May 16, 2008 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.