Leek Moths*


Hello! I am wondering when the leek moth is predicted to be active this season in the Toronto area? I want to plan for when I will be needing to put row covers on my seedlings to ensure they cannot lay their eggs this year! Thank you!


Thank you for your question for Toronto Master Gardeners.  Thank goodness we have an Ontario Ministry set up just to keep us informed about all kinds of invasive pests like the leek moth (or onion leaf miner).  You will need to keep an eye on the daily temperatures, according to OMAFRA (Ontario Ministry of Agriculture, Food, and Rural Affairs). The danger period is around 9.5 C.

From the OMAFRA website on Leek Moths

Eggs are laid singly on lower leaf surfaces whenever night temperatures are above 10°C-12°C. Females lay up to 100 eggs over a 3-4-week period. When eggs hatch, larvae enter leaves to mine tissues (leafminer stage). After several days, larvae move towards the centre of the plant where young leaves are formed. After several weeks of active feeding, larvae climb out onto foliage and spin their cocoons. Pupation lasts about 12 days, depending on weather conditions. Leek moth numbers and associated damage typically increase as the season progresses.

There is great deal of information on the website if you would like to find out more. Note especially some of the cultural controls for leek moths including crop rotation, removing old and infested leaves and positioning crops away from infested areas.  There is also good evidence that floating row covers protect emerging plants from moth damage.

Good luck with your veggies.