Combating Allium Leafminer

Cornell researchers presented key findings from their latest research on ALM at the Allium Leafminer Twilight Meeting held at the Hudson Valley Farm Hub

Combating Allium Leafminer

Researchers share tactics on saving onion and garlic

Since detected in 2015 in the northeast region, the Allium Leafminer has posed considerable challenges to onion and garlic growers.  By laying eggs inside leaf tissue, the pest leaves the plant vulnerable to damage, laying its claim with the oviposition mark, a trail of white dots where female insects have deposited their eggs. 

Ethan Grundberg shows infected leeks from the Farm Hub.

Allium Leafminer (also known as ALM) has been found in 14 counties in New York State. Researchers say it is making its way into Massachusetts and Vermont. The ALM maggots often lead to rot inside the crops, deeming them unmarketable. 

Growers who follow organic practices face an added challenge –  the limited number of insecticides they can use to battle the invasive pest. Over the past four years, Teresa Rusinek and Ethan Grundberg, researchers from Cornell Cooperative Extention Eastern New York Commercial Horticulture, have been studying the impact of ALM with the goal of finding solutions to help farmers. 

The research, “an envisioned multi-year process,” includes identifying which cultural strategies and insecticides work and “figuring out how we can reduce the number of insecticide applications and then can we develop more integrated programs,” Grundberg says. 

Leeks damaged by ALM. (Photo Credit: Cornell University)

A large part of the work is sharing what they have learned with regional growers including at conferences. In October,  Rusinek and Grundberg presented key findings from their latest research on ALM at the Allium Leafminer Twilight Meeting held at the Hudson Valley Farm Hub. 

Since 2018 the Farm Hub has served as the organic farming test site for the research project, while Migliorelli Farm in Red Hook has been the test site for both conventional and organic farming.  The fall 2018 trial at the Farm Hub focused on leeks and scallions and examined management methods, from the timing of sprays to the use of reflective mulch to the combination of various methods. This past spring the research was extended to test garlic. The biannual trials are critical since ALM has two flights a year, once in the fall and once in the spring. 


Sharing knowledge 

At the twilight meeting, Rusinek and Grundberg shared the following key takeaways from the fall and spring trials: 

  • Row cover is one of the most effective ways to eliminate damage, but it can be challenging for growers as it is often labor-intensive to put in.  
  • Reflective mulch with a couple of sprays of Entrust (an insecticide approved by the National Organic Standards Board) and with row cover can be a good tactic.
  • The insecticide Entrust mixed in a solution of M-Pede can be effective for better penetration of the waxy cuticle, if row cover isn’t used. 
  • Timing of spraying is critical too; based on the fall research on leeks, two applications of Entrust plus M-Pede work best, especially between three to four weeks after the first signs of ALM. 
  • Don’t spray too early. Within a consecutive six-week window of ALM flight, spraying during weeks three and four resulted in the lowest number of damaged plants. “During the middle of the flight, the ladies and gentlemen are all out and socializing so the chances you are catching the eggs as they hatch is much greater,” Rusinek explains. 
  • To check for infestation, growers should look for adult oviposition marks from a minimum of 10 plants at 10 sites on each field on a weekly basis until the activity is observed.

Grundberg notes the research findings, especially the timing of the sprays, can be useful for conventional farms too. Conventional farmers often apply Radiant to battle ALM, but “the results can look very similar,” he says referring to insecticides organic farmers use. Finally, the various ALM management tactics reduce infestation, but none has completely eliminated it. 


Ulster County farmers study a diseased leek at the ALM twilight meeting.

Looking ahead

An important part of the research is replicating the trial before “we are confident with the results,” Grundberg says. This fall the Cornell researchers repeated the trial on leeks, the final trial for this project held at the Farm Hub. With a new grant from Sustainable Agriculture Research & Education, the researchers are taking the ALM trial next to a commercial farm, in this instance Row by Row Farm in Hurley. Rusinek and Grundberg are committed to continuing the research and sharing the latest updates with the agricultural community. 

“I know growers want solutions and they want them now. We do our best to share the most updated results through our newsletter and through presentations at grower meetings, but from a more rigorous scientific perspective until we see replication we are more reluctant to boldly claim we have it figured out,” says Grundberg. 

 –Amy Wu 


For more information on Allium Leafminer 

New York State Integrated Pest Management
Cornell University
Penn State Entomology