By Blake Jackson
Farmers in Lancaster County, Pennsylvania, are urged to be on the lookout for allium leafminer (ALM) damage. Unseasonably warm weather has caused this destructive insect to emerge earlier than usual, posing a threat to onion, garlic, leek, and other allium crops.
ALM overwinters in the soil and becomes active in spring. Adult females puncture leaves to lay eggs, while both males and females feed on the sap. This feeding damage appears as a line of round wounds, most noticeable on onions.
Tim Elkner, an extension horticulture educator, advises growers to scout their fields now for signs of ALM activity. If row covers are your preferred method of protection, they should be installed as soon as possible.
Insecticides can be used for control, with the first application recommended two weeks after initial leaf damage is observed. Systemic insecticides are most effective as they target larvae feeding within the leaves. Due to the waxy coating on allium leaves, adding a surfactant to the insecticide spray is recommended.
Refer to the 2024/2025 Mid-Atlantic Commercial Vegetable Production Guide for a list of approved insecticides. Always read and follow label instructions, especially regarding pre-harvest intervals.
Early mornings, when temperatures are cooler, are the best times to scout for adult ALM on the tops of leaves. These flies are about a quarter inch long and resemble houseflies with orange-yellow heads. Finding scars is generally easier than spotting adult flies, particularly in windy conditions.
For updates on ALM activity throughout the growing season, Pennsylvania farmers can call the 1-800-PENN-IPM hotline (736-6476). Select option "1" for vegetables, then "2" for onion and alliums. Updated weekly during spring and fall, these messages will guide you on when to start and stop protecting your allium crops from ALM threats.
Photo Credit: gettyimages-erikkarits
Categories: Pennsylvania, Crops