Maybe you’ve seen evidence of these dastardly garden pests on the once-perfect leaves of your spinach or chard. Leaf miners have all but ruined some of my leafy greens in the past, but last year I vowed that it would never happen again!
To control garden pests without harmful chemicals, you need to first get really good at knowing each bug’s behavior and the telltale signs they’ve been in your garden. It’s easy to know when leaf miners are eating your plants because they leave these squiggly brown lines on the leaves. Besides ruining your pretty plants, if the infestation is serious, your plants will become too weak to recover.
Leaf miners come in several forms. Most often, adults are generic-looking black flies, and the adults will not harm your plants. Instead, they lay clusters of eggs in neat little rows on the leaves, usually the backside. Days later, the eggs hatch and the tiny larvae puncture the leaves and burrow inside where they continue to feed. They then drop to the soil around your plants to finish developing so they can emerge as adults. There are typically two or three generations in a season. For me, these garden pests are most troublesome in the spring and fall because they almost always attack my spinach, chard, and the foliage of my beets.
This year, I was ready for them. I do not use conventional pesticides in my garden, and I would never consider using harmful chemicals on leaves that I’m going to eat. Chemical pesticides not only kill garden pests, they also kill the dozens of beneficial insects your garden needs such as parasitic wasps that effectively kill leaf miner larvae. However, there are many ways to control these garden pests naturally, particularly in a small home garden.
- When you see infested leaves with the squiggly lines on them, remove those leaves immediately. Removing infested leaves quickly prevents the larvae from dropping to the soil and making even more adults. This is a population control measure, but it won’t save your plants in the short term.
- Look for the eggs of leaf miners on leaves. On my chard and spinach leaves, the little white eggs in clusters are easy to spot. I rub them off with my thumb to prevent them from hatching. This can be tedious, but it is doable in my garden. Rubbing off the eggs every couple of days is the most effective prevention I’ve discovered. The larvae never get a chance to eat my plants.
- Lay plastic mulch between and around your plants. This physical barrier prevents the larvae from being able to burrow in the soil when they finish feeding on the leaves and drop down. Again, this does not prevent short-term damage to foliage, but it is a great way to disrupt the leaf miner life cycle and control their population.
- Neem oil, a natural oil approved for organic gardening, can be sprayed on leaves to disrupt the larval development and lower populations of leaf miners.
- If you have a serious infestation and you are unable to manually rub off the eggs, your last resort could be spinosad, often marketed as Dead Bug. Only use it if you’ve tried everything else unsuccessfully or you have a very large garden. This organic garden pesticide is a neurotoxin that only kills insects once they begin eating your leaves.
As with any organic garden pest control, being proactive works far better than being reactive, after your plants are under attack. Take a few minutes each day to walk through your garden. In the morning, I stroll around with coffee. If I wait until evening, I bring an icy cold beer! Really look at your plants and take note of what’s happening in your garden, what is different than before. Often, your garden will teach you some great lessons about nature, survival of the fittest and how we can all coexist. Understand, watch for and reduce leaf miners to increase your harvest of cool season leafy greens.