On April 22, Penn State Extension announced field scouting has detected first emergence of the allium leafminer, Phytomyza gymnostoma, an invasive fly species, in Perry, Lancaster, and Northumberland Counties. They expect the adult flight to occur over the next two to five weeks.
Extension recommends farmers protect their crops over this time to manage this pest.
Background
The allium leafminer, Phytomyza gymnostoma, an invasive fly species that originates from Europe, is now confirmed in 5 states.
The fly infests plants in the Allium genus, including leeks, onion, garlic, chive, shallot, green onion, wild garlic, chives, and ornamental Alliums.
Allium leafminer overwinters as pupae and emerges in the spring. Field scouting has detected 1st emergence between April 16-19 in Perry, Lancaster, and Northumberland counties. We expect the adult flight to occur over the next 2 to 5 weeks. Protecting your crops over this time will go a long way towards managing this pest.
Adult females puncture leaves in a linear pattern with their ovipositor for feeding and egg laying (Figure 1). Leaves from infested plants can be wavy, curled and distorted (Figure 2). Larvae mine leaves moving towards and into bulbs and leaf sheathes (Figure 3) where they pupate (Figure 4).
Peel back the leaves to find the insect. Both the leaf punctures and mines serve as entry routes for bacterial and fungal pathogens.
After this spring flight, the larvae or pupa have a summer aestivation (dormancy) period and a fall flight.
In past years, fall flight in Pennsylvania has started anywhere from very late September or well into October. If you can protect your crop during spring and fall flight times, you should be free of damage.
The adult fly (Figures 1, 5, 6, 7) has a charismatic orange face, yellow “knees” (end of femurs), and matte black body. At 3mm-4mm, the adult is small (larger than a fruit fly but much smaller than a house fly). Eggs are laid in or on plant tissue, and larvae are well embedded into the plant tissue.
The timing of planting and harvest affect risks of damage. We seem to be getting most damage to allium crops that are showing strong vegetative growth at the time of adult flight activity.
Row covers or insecticides during the flight period should prevent damage. We have found efficacy using neonicotinoids (Scorpion, Assail), diamides (Exirel), spinosyns (Entrust, which is OMRI-labelled, Radiant), and pyrethroids (Warrior).
A spreader-sticker is recommended when applying insecticides to the waxy leaf coating of alliums.
Click Here for the Penn State Extension advisory.
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