There is a new pest in our area first found in Lancaster County, Pennsylvania, in December 2015. It is the Allium leafminer (Phytomyza gymnostoma) which attacks Allium plant species. Leeks tend to be the most damaged host, but all Allium species (onions, garlic, chives) may be attacked. Adult females have yellow/orange heads and yellow ‘knees’ (fig. 1) and make repeated punctures in a leaf with their ovipositor. These punctures are organized in a straight line going down the leaf from the tip (fig. 2). Damaged leaves can appear wavy, curled or distorted.

Larvae mine leaves, and move into bulbs and leaf sheathes where they pupate. Both the leaf punctures and mines serve as entry routes for bacterial and fungal infections. High rates of infestation have been reported from some Allium fields in Pennsylvania.

The reason I am telling you this is because we do not know if this pest will attack Allium plant species in the landscape. Not only would this cause possible landscape plant loss, but these infestations would also act as a breeding area for the pest to build its population early in the spring and later in the fall; the two times of year when it is most active. If you see any similar damage to Allium species or the fly itself on landscape plants, please let me know. You can submit your photos to the Home & Garden Information Center’s Ask an Expert service and we will take a look at them.

By Jerry Brust, Senior Agent and IPM Vegetable Specialist, University of Maryland Extension