Allium Leafminer

White lines or trails in leaves are a symptom of leafminers.

f you are growing fall leeks or garlic or other Allium species you need to, for the next month or so (September-first freeze) watch for the tell-tale marks left by Allium leaf miner.

If you grow leeks or onions or other Allium species, now and for the next few weeks is the time to watch for the tell-tale marks left by Allium leaf miner. Allium leaf miner Phytomyza gymnostoma tell-tale marks consist of several small round white dots (made by the female’s ovipositor) in a row that appear on the middle towards the end of leaf blades (fig. 1) of their preferred hosts of leeks, onions, garlic and other Allium species.

The pest of onion, leek and garlic, the Allium leafminer Phytomyza gymnostoma, is active now and is showing up in more counties in Maryland. Adults will be active in Maryland for the next 4-6 weeks. This pest was first observed in Maryland in Cecil Co. in 2017 and then in Baltimore county last year, but now the fly’s tell-tale marks (fig. 1) of small round white dots in a row have been found by Robert Trumbule an onion grower in Prince George’s county. This pest was originally found in Lancaster county Pennsylvania in December 2015. Unfortunately, it is my guess that the pest is now probably in many northern/central areas of Maryland.

I know, I know I wrote one of these just a few weeks ago and here it is again. Why a second article about this pest? I am writing now because I was a bit amazed and alarmed by some field observations in the last 2 weeks. I was on a farm in western Howard county on April 17th in a fairly recently planted onion field with the grower (keeping a safe social distance) looking for tell-tale signs of Allium leaf miner.

The allium leafminer Phytomyza gymnostoma (also known as the onion leafminer) has recently been detected and confirmed from infested leeks in Lancaster County, PA. This is the first confirmed infestation in the Western Hemisphere.