Monitoring and Managing Leek Moth in Garlic and Leeks

The effects of leek moth in garlic and leek fields are becoming more noticeable across Ontario. Leek moth larvae attacks all parts of the plant except for the root

Travis Cranmer - Vegetable Crops Specialist

Wounds created by larvae will act as an entry point for secondary pathogens. In leeks, the larvae mine the leaves making the crop unmarketable and in garlic the larvae can reduce yields, cause rots, and make their way into the bulb before harvest.

Monitoring using lures with a leek moth pheromone in a delta trap with a sticky card will give you an indication on the severity of the leek moth population in the crop.

These sticky cards will not remove enough moths to significantly reduce the population. Management strategies targeting the leek moth will be more effective when the population peaks are identified and used to time insecticide applications.

Two delta traps are generally used to get an average number of moths per field. These traps are generally placed near the edge of the field closest to where garlic or leeks were grown in the previous year. Traps can be placed just above the crop canopy and a good distance apart.

Figure 1. - Adult leek moth on sticky card accented by the tip of a paperclip.

The sticky traps catch adult moths which are small (5-7 mm), reddish brown, and have a white triangle shaped spot that is sometimes visible depending on how long the moth has been on the trap (Figure 1).

Sticky cards are replaced weekly and the number of leek moths between the two fields can be plotted to give you a visual of the population peaks throughout the season (Figure 2). There are generally three population peaks per year with the first two causing damage in garlic and all three generations can cause feeding damage in leeks.

Figure 2. – Leek moth populations tracked by two Delta 1 traps in one county in Ontario. Colours correspond to different years; Orange 2019, Red 2020, Purple 2021 and Green 2022.

Figure 3. – Delta 1 trap monitoring for leek moths in a garlic field.

Delta 1 traps with removal liners allow for new sticky cards to be added on a weekly basis (Figure 3). Other traps without removeable liners cannot be used for long periods of time and lose their stickiness once they become full of insects or blowing dust. Attach lures with the leek moth pheromone using a paperclip to the inside wire of the trap so it can hang above the sticky card liner. Distributions Solida (info@solida.ca), based out of Quebec, are the primary supplier of these traps in Canada. To monitor the garlic or leek field from May until September with two traps, the following would be required:

2 x wooden stakes

2 x Delta 1 traps with hanger

30 x Delta 1 trap liners / sticky cards

12 x leek moth pheromone lures

Monitoring can start as early as April as adult moths emerge from overwintering spots when night temperatures reach 9.5°C. Insecticide applications have found to be most effective when they target the second-generation peak that generally occurs between the first week of June to mid-July in Southwestern and Eastern Ontario. Generally, 7-10 days after the date of the peak moth capture will target the larvae as they they feed on the leaf moving out from the meristem.

Bt products such as BioProtec CAF, BioProtec Plus, XenTari WG and Entrust can be used depending on your organic certification body, and Delegate WG and Success are additional options for conventional garlic and leek growers. Leek growers also have Coragen as another conventional insecticide option. All insecticides are most effective when they make contact with the larvae. 