Leek Moth Management

Leek moth has slowly been increasing its presence across Ontario and into the maritimes and Quebec since it was found in Ottawa in 1993. Leek moth overwinters as an adult moth in brambles and lays its eggs on the meristem of Alliums consuming all parts of the plants except for the roots.

Leek moth has three distinct adult flights per year, and based on monitoring throughout Southern Ontario, these population peaks appear to be early-May, early-July, and mid-August. Leek moth prefers leeks and garlic, but will also feed on onions, shallots, and chives. Leeks are at greatest risk to leek moth because the inner portions of the leaves must be marketable, and the crop must endure all three larval generations of this pest.

Once a leek moth population is established in an area, there are two effective management methods; insecticides and exclusion nets. In order for exclusion nets to be effective, they must be set up prior to the first leek moth flight, which is thought to occur when night temperatures remain above 9.5 °C for two consecutive nights.

Insecticides are most effective when they make contact with the larvae or the part of the plant that leek moth larvae are actively feeding on. Insecticides containing Bt (such as BioProtec CAF, BioProtec Plus, XenTari WG) should be applied to the crop in the evening or on cloudy days since these products can be susceptible to sunlight degradation.

Should you consider monitoring for leek moth? If you are applying an insecticide to manage leek moth, a leek moth pheromone in a delta trap with a sticky card will give you an indication of when to time your insecticide applications.

In garlic, an insecticide application is most effective if applied a week after the second leek moth flight, which generally occurs between mid-June and late-July depending on the year. If two insecticide applications are to be applied, place them 3 and 10 days after the peak trap capture. In leeks, insecticide applications a week after each population peak is thought to target the greatest number of larvae with the fewest number of 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. Monitoring can start as early as April as adult moths emerge from overwintering spots when night temperatures reach 9.5 °C for two consecutive nights.

Leek moth on sticky card — **Figure 1**. Leek moth highlighted by the end of a paper clip on sticky card.

The sticky cards 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).

**Figure 2.** Average number of leek moths per sticky trap per day at seven garlic fields and one leek field within the surveyed counties of Grey, Huron, Oxford, Perth, Prescott-Russell, and Renfrew, 2024. No leek moths were observed at either location in Huron county in 2024.

Sticky cards should be 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). Delta 1 traps with removable 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: