Allium Leafminer Moving South in Maryland

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The new pest of onion, leek and garlic, the Allium leafminer, is moving south in Maryland. It was first observed in Maryland in Cecil Co. in 2017, but now the fly’s tell-tale marks (Figs. 1 and 2) have been found in a Baltimore City chives planting. This new pest was first 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. New transplants or seedings of onions or leeks should be watched closely for the tell-tale signs of the fly’s damage which are several very small white dots in a row along the leaf of an allium plant (Figs. 1 and 2).

Figures 1 and 2. Tell-tale marks on allium leaf made by Allium leafminer females

Penn State has a great deal of good information about the new pest which can be found at: Penn State Allium Leafminer Pest Alert page. Growers should look for these tell-tale signs on any newly planted allium species, but especially on leeks. You can cover any Allium planting with row cover to keep the flies off or if needed treat with insecticides as found in the 2019 Mid-Atlantic Commercial Vegetable Recommendations guide.

Allium Leafminer Active in Maryland

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The new pest of onion, leek and garlic, the Allium leafminer, is active now in our area. This new pest was first found in Lancaster County Pennsylvania in December 2015. It has since been found in Maryland in only a few northeastern counties, but my guess is that the pest is probably in many northern/central areas of Maryland. New transplants or seedings of onions or leeks should be watched closely for the tell-tale signs of the fly’s damage which are several very small dots in a row along the leaf of an allium plant (Fig. 1). Figure 1 is an excellent picture by Sarah May of Penn State, that not only shows what and where the feeding is observed on a plant but also the relative size of the oviposition/feeding damage and what you should look for. Penn State has a great deal of good information about the new pest which can be found at: Penn State Allium Leafminer Pest Alert page. Figure 2 shows the adult female as she is making the incisions into the allium leaf causing the white spots. Growers should look for these tell-tale signs or the fly itself on any newly planted allium species. You can cover any new allium plantings with row cover to keep the flies off or treat with insecticides.

Figure 1. Oviposition/feeding spots (red circles) on onion transplants from Allium leafminer

Figure 2. Allium leafminer female adult on onion leaf

New Pest, Allium Leafminer, Present in Neighboring States

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

The allium leafminer (ALM) or onion leafminer is an invasive species that was detected in Lancaster, PA in 2015. This was the first confirmed detection in the Western Hemisphere. Since this detection, it has spread to New Jersey, New York, and Maryland. It has not been detected in Delaware but is something you should be aware of.

The allium leafminer is known to infest species in the genus Allium. This includes leeks, onions, garlic, chive, shallot, and green onion. The adults, small grey or black flies with a yellow or orange marking on the top and front of head, emerge in late winter through spring (March-May) and begin laying eggs at the base of plant stems. The larvae mine leaves, moving downward to the base of leaves or into bulbs where they pupate. Pupae may move into soil. During the summer months, ALM undergoes diapause in the pupal stage before developing into adults which emerge in the fall (September/October). This generation also attacks Allium spp. before overwintering as pupae.

Here are a couple links from Penn State University and University of Maryland for more information on allium leafminer including pictures of adults, pupae, monitoring, damage, and management:

http://ento.psu.edu/extension/vegetables/pest-alert-allium-leafminer

https://extension.umd.edu/learn/allium-onion-leafminer

If you suspect you have damage or a life stage of the allium leafminer, please contact Steve Hauss at the Delaware Department of Agriculture (302-698-4500 or Stephen.hauss@state.de.us) for official confirmation since this pest has not been detected in Delaware.

Pest Alert – Allium Leafminer

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

The allium leafminer (also known as the onion leafminer) has recently been detected and confirmed from infested leeks and onions in Lancaster County, PA. This is the first confirmed infestation in the Western Hemisphere. HOWEVER, this insect has not been detected in Delaware. If you think you may have observed damage or a life stage of the allium leafminer, it is important that you contact Steve Hauss at the Delaware Department of Agriculture by email (stephen.hauss@state.de.us) or call (302) 698-4500 for official confirmation since this would be a new detection in Delaware.

The following pest alert written by written by Shelby Fleischer, Department of Entomology, Pennsylvania State University, University Park, PA, and Tim Elkner, Cooperative Extension, Lancaster County, PA and edited by Dan Gilrein, Cornell Cooperative Extension of Suffolk County provides information on damage symptoms, insect identification and life history, monitoring and potential management options

http://ento.psu.edu/extension/vegetables/pest-alert-allium-leafminer