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Tunnels in Leaves: Leaf Miners

Tunnels in Leaves: Leaf Miners

What is a "Leaf Miner?"

If you're seeing a strange "tunnel-like" pattern in your plant leaves (pictured above) or blotches that form in leaves along with a tunnel (pictured below), you likely have leaf miners. "Leaf miner" is a term used to refer to insects that dig (tunnel) through the cells of a leaf and leave their larvae behind. There are two main factors that make this particular ailment so difficult to treat:

  1. The larvae is inside the leaf structure where sprays can't reach them. 
  2. Different types of insects can cause "leaf mining" and therefore, it's not always easy to determine what kind of control/spray you might need to deter them.
Leaf miners in my sorrel

Leaf miners in my sorrel

Controlling Leaf Miners

It seems like I get leaf miners every year, and based on conversations I've had with gardeners around here, it's pretty common. So, what's a gardener to do? Even without knowing which insect is causing the damage, most gardeners will have success with these two simple steps: 

  1. Remove affected leaves from the plant. There's no saving them now.
  2. Spray underside and tops of leaves with an organic pesticide - either Neem Oil or Spinosad.

I've only used Neem Oil myself, but may try Spinosad. Neem oil is made from the extract of the seeds of a Neem tree and can be purchased in concentrated form or in a ready to spray bottle from most garden centers. The reason I'm considering the switch from Neem oil is that I'm only having moderate success with it this year. It took care of the leaf miners when they were impacting my beets, but they're pretty persistent on my sorrel.

Spinosad is a fermented version of a naturally occurring soil bacterium. I was initially concerned about Spinosad after reading about the concern that it may be harmful to honey bees. However, I've read several scientific studies (one example: NIH abstract) that have determined that after it has dried (about 3 hours), it is not harmful to honey bees. You should still use caution in when you spray it.

Don't spray Spinosad near water or near bee colonies and only spray Spinosad in the evening hours (when bees are not active in your garden and it will be dry by the time they are). 

Leaf miners aren't the worst thing you can get in the garden, but left untreated, you may lose the plants they're affecting. As soon as you see the tunnels, just remove the leaves and spray the remaining leaves. Keep spraying here and there, particularly after a rain that may wash away the spray from the leaves.

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