Allium Leafminer – A New Invasive Pest

The allium leafminer (also known as the onion leafminer) came originally from Central and Eastern Europe, where it’s a serious pest on leeks, onions, and chives. It has been spreading outwards in the last 20 years and is now found throughout Europe. Later, it was spotted in Lancaster County, PA, in December 2015, making it the first confirmed infestation in the western hemisphere.

The pest is seen targeting onions, leeks, garlic, chives, shallots, as well as green onions, with leeks being described as the most damaged host.

Leaf mining takes place mostly from April to May and from October to November. However, the damage is most obvious later, once rotting has set in, so is usually seen in overwintering leeks between December and February, and in onions in June.

One of the first symptoms you will notice on plants is wavy, curly, and distorted leaves, upon closer inspection, you will be able to see puncture marks along the sides of the leaves toward the distal end.

The fly larvae mine the plant leaves and move toward the bulb and leaf sheaths where they pupate. Exactly where they pupate in the plant may vary depending on bulb and leaf size. To check for larvae, the plants must be pulled out of the ground and the leaves pulled back.

Recent news reported is:

Allium Leafminer Makes Early Appearance

  • Apr 10, 2020

Penn State Extension photo Marks made by the female leafminer when she lays her eggs.

Leaf symptoms of adult allium leafminer activity were observed on scallion and wild garlic in Lancaster, York and Perry counties on March 17 and 18. This is about one month earlier than we normally see the spring flight of this potentially devastating pest of all allium crops — onion, shallot, garlic, chives, leek — in this part of Pennsylvania.

I have found adult flies and damage on scallions at the Penn State Research Center in Landisville and have noted increasing fly numbers and damage on chives, onions and ornamental allium in my home garden. Based on the amount of observed damage and the number of flies seen, the population is building and more flies will be seeking allium crops to lay their eggs in over the next few weeks.

Controls sought for pest threatening Black Dirt onions

By Judy Rife │Times Herald-Record │March 5, 2019

PINE ISLAND – Preliminary research has begun to identify controls for the allium leafminer, the new pest that poses a threat to Orange County’s signature onion crop, but the battle is far from over.

That is the message growers heard Tuesday at Cornell Cooperative Extension’s annual onion school, a day-long event held at the Pine Island Fire Department.

“The question everybody has that we can’t answer yet is ‘Will it cause economic damage to the bulb onion crop?’ ″ said Brian Nault, a professor of entomology at Cornell University, explaining the pest is still getting established.

“So far,” he continued, “seeded and transplanted onions have escaped, which is not the case with garlic, leeks, spring onions and chives where we have seen as much as 75 percent damage.”

Cornell’s team is working in tandem with a team at Penn State. The two universities received $325,000 from the U.S. Department of Agriculture last year to study controls for the leafminer over the 2019 and 2020 growing seasons.

New insect pest a threat to onion and related crops in Pennsylvania

By Chuck Gill │May 12, 2016

UNIVERSITY PARK, Pa. — An insect never before found in the Western Hemisphere has been discovered in Pennsylvania, and agriculture officials are asking growers and home gardeners to help monitor and manage the new invasive pest.

“It is now present throughout Europe, reaching the United Kingdom in 2004,” Fleischer said. “It recently has been reported in Asia, Turkey, Russia and Turkmenistan.”

“High rates of infestation have been reported,” Fleischer said. “There can be from 20 to 100 pupae per plant, and 100 percent of plants in a field may be infested.”

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