Fall Flight of Allium Leafminer Observed in Southeast PA

Allium leafminer (ALM) was observed on September 15, 2025, on green onions at the Southeast Agricultural Research & Extension Center in Manheim, Pennsylvania, by Tim Elkner. This pest, which feeds on Allium crops including green onions, leeks, garlic, shallots, chives, and onions, causes damage not only by larval feeding but also because adult females puncture leaves to lay eggs. These punctures leave a characteristic linear series of round white dots in leaves that are particularly apparent on green onions and scallions. Adult ALM are small flies with orange patches on their head and can be seen resting on the tips of allium leaves. Larvae tunnel into the leaves, moving down towards the bulbs. Larvae develop into small reddish-brown pupae in the bulbs or exit the bulb and pupate in the surrounding soil.  

Historically in the Northeast, the fall generation of ALM begins its adult flight in mid-September and remains active through October. ALM overwinter as pupae in leaf tissue or nearby soil and produce two generations per year: one in spring and one in fall. Once adults are flying, Allium crops should be scouted regularly. If row covers are being used to protect crops, they should be deployed now to avoid trapping flies under the covers and remain in place until the first hard freeze.

Chemical controls for ALM should begin during the adult emergence period, and effective synthetic control options include foliar applications of Scorpion or Venom (dinotefuran), Exirel (cyantraniliprole), and Radiant (spinetoram). Entrust (spinosad) is an organic option that provides good control when applied with M-pede twice in the 2-4 weeks following early adult emergence. Under high ALM pressure, a rotation with Pyganic may be required.