By Blake Jackson
Allium leafminer (ALM) was detected on September 15, 2025, on green onions at the Southeast Agricultural Research & Extension Center in Manheim, Pennsylvania, by Tim Elkner.
This pest attacks a variety of Allium crops, including green onions, leeks, garlic, shallots, chives, and onions.
Damage occurs both from larval feeding and from adult females puncturing leaves to lay eggs. These punctures appear as a distinctive linear pattern of round white spots, most visible on green onions and scallions.
Adult ALM are small flies with orange markings on their heads, often seen resting on leaf tips. Larvae tunnel through the leaves toward the bulbs and eventually pupate as small reddish-brown forms either inside the bulbs or in nearby soil.
In the Northeast, the fall generation of ALM typically begins adult flight in mid-September, continuing through October. The pest overwinters as pupae within leaf tissue or soil, producing two generations annually: one in spring and one in fall.
Once adults are active, Allium crops should be scouted frequently. If row covers are used, they should be installed now to prevent trapping adults beneath the covers and kept in place until the first hard freeze.
Chemical management should coincide with adult emergence. Recommended synthetic insecticides include foliar applications of Scorpion or Venom (dinotefuran), Exirel (cyantraniliprole), and Radiant (spinetoram).
Organic options such as Entrust (spinosad) can be applied with M-Pede in the 2-4 weeks following early adult emergence. Under heavy ALM pressure, rotating with Pyganic may be necessary for effective control.
Photo Credit: gettyimages-dmytro-diedov
Categories: Pennsylvania, Crops, Fruits and Vegetables