How do I keep leaf miners out of my garden?
Written by Derek Barber, FOAG Volunteer
Leaf miners seem to be having a big year this year and a lot of us are seeing tunnels in our leafy greens – including those at our community garden, Edible Allan Gardens. Leaf miners are usually found in members of the Chenopod family (beets, chard and spinach), but can be found in other plant families as well.
The recent mild winter allowed most of their larvae to survive and hatch in April. Since then, we’ve been getting wave after wave of leaf miners. They start as eggs that are laid inside the leaf of a plant. The larvae eat their way through the leaf (creating the visible tunnels) for approximately two weeks, and then emerge and burrow into the soil beneath the plant. Two to three weeks later, they emerges from the soil as adult flies. The adults then lay eggs into the plant leaves, and the cycle repeats itself.
Leaf miner tunnels Photo: Derek Barber
Here are the two steps that I take to eradicate leaf miners from my garden. They’re manual and you need to do both steps regularly, but it’s effective.
#1 – Stop the leaf miner lifecycle by thoroughly checking your plants every few days for tunnels or papery blotches in the leaves. Any affected leaves should be cut off from the plant, placed in a plastic bag, sealed and garbaged. This process takes away all of the larvae before they emerge from the leaves. The leaf miner lifecycle ends when there are no more leaf miner larvae left to morph into adults. Naturally, this only works if you spot them all before they emerge, and if your neighbours with gardens do so as well.
# 2 – To improve your odds of getting them all without sacrificing your harvest, you should also regularly check for eggs. They are tiny rice-grain-shaped white eggs that will be on the undersides of the plant leaves. Any eggs that you find should be removed or squished.
Leaf miner eggs. Photo: Derek Barber
While I prefer the two processes mentioned above, here are three less-manual options:
Use an organic pesticide solution like spinosad, which is harmless to most beneficial insects. Spray it on all infested leaves for the larvae to ingest.
Use neem oil, which makes it difficult for the flies to lay eggs on your plants and it reduces the number of eggs that hatch. It may affect some beneficial insects, so avoid spraying it near any flowers and try not to spray the soil with it. Reapply every week or two.
Place floating row cover over top of your vegetable plants, which prevents flies from landing and laying eggs. While this method is effective, the downside is that you need to take the row cover off every time you want to check on your vegetables (e.g., to look for tunnels) or every time you want to harvest your veggies.
I listed the options above in order of my own preference; however, choose the one that works best for your schedule and gardening preferences. If you have time, I recommend the manual leaf inspection and removal. However, that only works if you are thorough and if you think the issue is coming from your own garden; otherwise you may need to choose one of spinosad, neem oil, or row cover.
