Spotted lanternfly (Lycorma delicatula) is getting a lot of attention as the latest big pest threat in the Mid-Atlantic, but it’s not the only new and serious problem to pop up in our area recently. Allium leafminer (Phytomyza gymnostoma, or Napomyza gymnostoma), also known as onion leafminer, is another invasive insect to watch out for in your garden. Native to parts of Europe, it was first spotted in this country in Lancaster County, Pennsylvania, in late 2015, and as of this spring, allium leafminer has been identified in New York, New Jersey, Massachusetts, and Maryland as well.

As indicated by the name, this pest affects pretty much any species of allium. Besides edibles like onions, leeks, garlic, chives, and shallots, it can also damage ornamental alliums. I first noticed its presence in my Bucks County, Pennsylvania, garden last summer, and the adults appeared again this year the last week of…