White Squiggly lines on Leaves (Leaf miners and what to do)

Leaf miners are a fairly common garden insect problem. And it is easy to spot when your herbs and vegetables are under attack as the leaf miners leave white squiggly lines on your plants’ leaves.

Any plant can be attacked by leaf miners but vegetables seem to be the most affected. 

The white dots and squiggly lines left behind by the leaf miners are of course not attractive. And for every one growing leaf vegetables or herbs for consumption the leaf miners could ruin your entire harvest.

What are leaf miners

Leaf miners are larvae living and feeding inside the leaves of our plants, herbs and vegetables.

Flies, moths or beetles lay eggs inside the leaves of our plants. Within a week or so the eggs hatch and the larvae will start eating away on the inside of our leaves. 

The larva is basically feeding on the plant tissue between the surfaces of the leaf. And the white lines are dead tissue showing where the larvae have been feeding.

Sometimes leaf miners are an annoying problem

I view leaf miners as a threat to our garden as we grow a lot of leaf vegetables and herbs. Leaf miners can effectively ruin the harvest from an entire plant and more. 

But as I said it depends. I do not worry too much about leaf miners on leaves when I, for example, grow parsnips, tomatoes, horseradish or turnips. The leaf miners will not kill the plant. And I do not intend to eat the leaves.

I will simply remove the leaves as I see them as I do not want the problem to spread. Do make sure you dispose of leaf miner infested leaves properly. Do not put them in your compost. Squeeze the leaves hard between your fingers to kill the larva, before disposing of them.

Remember, do not put the leaves into your compost!

But leaf miners can also ruin your entire harvest

We grow lots of leafy vegetables. Apart from our love for all herbs we also grow many different types of lettuce, mangold and cabbage as well as tatsoi and corn salad

When leaf miners attack it is a real problem as they can ruin the entire harvest if left unchecked.

And I really do not want to eat leaves that show signs of leaf miners. 

We have a few different ways to deal with leaf miners depending on the type of herb or vegetable and how spread out or mature the infestation is.

Writing this article about white squiggle lines

We always use our own photos on Nordic Lavender. This is why the backgrounds on our photos are somewhat limited. 

But on the positive side you as a reader know we are writing about actual results, facts and from experience.

And this article about leaf miners and white squiggly lines has been waiting to be written a long time.

There are always many pots of herbs and vegetables on the go in our garden, our greenhouse as well as indoors. 

In the winter we focus on certain herbs and also experiment with hydroponics and growlights. But spring, summer and fall are always full of planting, growing, testing and harvesting. 

And as we have had plants with leaf miners in the past, I was sure that it was just a matter of time before they would come back again and find a new plant. After all, we do not use preventative pesticides – organic or not.

Leaf miners on basil plant
Leaf miners leaving white squiggly lines on basil plant

We avoid commercial pesticides – these may kill the good bugs as well if not used with care. We try to maintain a balance, and instead deal with problems or challenges when and if they occur. 

But this year all our herbs and vegetables did really well. I of course like to think that it is all about my soil recipes. But alas, no.

A couple of days ago we saw the tell-tale sign on a couple of our basil plants.

And these are the leaves you can see in the image above. 

How to get rid of leaf miners

The trick when dealing with leaf miners is early detection to contain the problem.

If you are a fan of commercial pesticides there are plenty available that say they will fix the problem. However, they are expensive – and do remember that the problem is inside the leaf.

And how do you spray inside the leaf? Of course you cannot.

This is another reason why we do not use commercial pesticides when dealing with leaf miners. You would need to catch the larvae as they emerge from the leaves and it seems hard to me.

We have instead come up with different methods that work for us depending on the level of infestation and type of plant. 

1. Early detection will make all the difference

We always detect leaf miners too late. After all, we detect them when we spot the damage they have caused to our plants.

Still early detection is important. I try to spot leaf miner attacks early on. And it is really quite easy. Just look at the leaves on your herbs and plants every now and then. Ideally every day.

And if you find black dots on the back of leaves or any other thing that looks out of place – deal with it straight away.

2. Dealing with leaf miners on plants where we do not eat the leaves

When we spot leaf miners on the leaves of for example tomato plants we simply remove the leaves and sometimes the entire branch.

Use your own judgement but if there are no fruits on the branch and many leaves are infested it may be better to simply remove the entire branch. 

Keep an eye on the plant and keep monitoring for additional signs of infestation.

If the problem comes back, keep removing leaves.

If it becomes apparent that removing branches and leaves will not rid you of the leaf miners we have to make a decision.

Treat or destroy the plant

We have already explained that we do not like to use commercial pesticides or sprays. We like to know what we put on the plants that will yield food for our families.

But there are some methods that we do use. The following mixed solutions can be sprayed on both sides of the leaves to treat and soften the impact of a leaf miner infestation.

Always treat the plants early in the morning or late evening and never expose the treated plants to sunlight that same day.

Also, when mixing your solutions, test it on 1 or 2 leaves first and wait 1 or 2 days to see how the plant reacts. 

  1. Soap and water mixture
    Mix 1 tablespoon of natural eco-friendly liquid dish soap with 1 liter of room temperature water.
  1. Organic cold pressed Neem oil with water mixture
    Use neem oil for agriculture use. Mix 5 ml of neem oil with 1 liter of room temperature water. 

Do not buy the type of neem oil that is meant for treating nails, skin and hair. This type of neem oil is not water soluble. You will end up having to add soap to create a solution you can spray. If you do not, the oil will simply float on top of the water. 

It may seem drastic to suggest you should destroy the plant. But if you have 10 tomato plants and 1 is badly infested it may be your best option. 

If you cannot cure the plant you will risk infesting the other tomato plants as well.

3. How to treat Leaf miners on herbs or leaf vegetables

When our herbs or leaf vegetables are infested with leaf miners we could lose our entire harvest. 

We have several different steps. Where we start depends on the level of infestation. You could also say depending on how good we are at detecting the infestation early.

  1. One or two infested leaves
    Inspect the plant and then simply cut or pinch the affected leaves.

    It may be obvious to you but place the pot high up when you inspect the back of the leaves.

    If you see black dots or anything else on the surface of the leaves, simply brush it off using your fingers.
  2. Several infested leaves on a branch
    Remove the infested leaves. If there are many infested leaves, consider removing the entire branch.

    Now in our case we have leaf miners on Thai basil as well as common or sweet basil plants. We removed several leaves but also some branches. On some branches the top leaves were healthy but the lower leaves were infested. 

    We removed the infested leaves and placed the cuttings in separate containers with water to propagate new plants. 

    We used separate containers for each cutting, as the leaves could be at the early stages of infestation and we hope to rescue some if not all cuttings. 
  3. Trim the plant back (if it will regrow)
    Many herbs will grow back and grow bushier if you trim them back.

    One of the Thai basil plants had infested leaves on several branches.

    It was a well developed plant and it was difficult to inspect the leaves properly.

    Here we simply cut it back to create nice size cuttings. We automatically cut off all leaves but the top crown that we proceeded to inspect properly. 

    Now we hopefully have several new Thai basil plants on the go.
  4. Destroy the plant or remove sections to stop spread
    We never treat leaf vegetables or herbs that are infested.

    Not even with organic or eco-friendly methods or mixtures.

    We have the luxury of having several garden beds, pots, containers, vegetable and herb gardens and a greenhouse. We prefer to destroy the plant to try to remove the problem.

    If you want to treat your herbs or leaf vegetables please refer to the “Treat or destroy the plant” section above for two mixtures we use for tomatoes, cabbages, turnips and parsnips. 

    We plant lettuces, cabbages, spinach, tatsoi and corn salad in rows. If we notice an infestation we try to locate where it starts and where it ends. 

    We then proceed to remove that section including one “healthy” plant on either side of the infested plants.

We know this can happen at any time during the season. This is one reason why we recommend you plant herbs and leaf greens in batches throughout the season. This way you have leaf greens to harvest at different times and also hopefully always healthy herbs and plants to enjoy.

Meet the author: Mattias is an experienced gardener spending most of his free time on his knees among herbs, plants, and garden vegetables. For the past two years, he has been sharing gardening projects and how-to tutorials on the NordicLavender website and YouTube channel.