How to manage leafminers in your garden
As gardeners, we aim to keep the crop healthy and get the most out of it. But nature has different plants. Plants feed and are food for other living organisms. Some of them are our interests. Leafminers are probably the most common trouble for framers.
Occasionally, we see doodles and patches in our plants’ leaves. This post discusses leafminers, how to prevent them, and how to treat them with or without chemical pesticides.
What are leafminers?
You may have noticed some curly leaves in your garden. If you crack open the curly part, you may see insect larvae or eggs. When insects breed, they lay their eggs underneath the leaves.
Once the eggs latch and the larvae are out, they feed on the leaves. They keep traveling and feeding all over the leaf until they reach their next phase. When they feed, they feed inside the leaf, not on the leaf. Thus, leafminers effectively create tunnels inside the leaves. When we see them, we should be able to find a path that looks like someone has put a doodle on the leaf.
We call them leafminers. They are caused by insects like flies, moths, and beetles. There are several varieties of leafminers, each attacking different types of plants. Here’s a table of different leafminers and the plants they attack.
| Type of Leafminer | Examples | Affected Plants |
|---|---|---|
| Lepidopteran Leafminers | Tuta absoluta (Tomato leafminer) | Tomatoes, potato, eggplant, pepper and tobacco |
| Phyllocnistis spp (Citrus leafminer) | Citrus trees (orange, lemon, lime, etc.) | |
| Dipteran Leafminers | Liriomyza spp (Serpentine leafminer) | Spinach, melon, lettuce, peppers, carrots, cucumbers, celery, squash, tomatoes, eggplants, beans, peas, beets, potatoes, and onion |
| Agromyzidae family (various leafminer flies) | Various vegetables, including tomato, cucumber, and melon. | |
| Coleopteran Leafminers | Chromatomyia syngenesiae (Chrysanthemum leafminer) | Chrysanthemums |
| Marmara spp. | Various ornamental plants | |
| Hymenopteran Leafminers | Fenusa pusilla (Birch leafminer) | Birch trees |
Most leafminers create doodle-like random tunnels of dead tissue on the leaf’s surface. These tunnels will eventually turn brown, too. Yet, leafminers can create patches too. Remarkably, the spinach leafminers create random doodles, eventually building up like a patch.
Which plants are susceptible to leafminers?
Leafminers affect almost all types of plants. I’ve heard herbs like basil keep them in control. But I’ve experienced basil plants themselves having leafminer infestation.
Yet, the seedlings are the most vulnerable to leafminers. Because leafminers rarely feed on mature, solid leaves, they target the soft, young leaves. Noticeably, the cotyledon from the seeds and the first true leaves are excellent incubators for insect larvae.
I’ve noticed that Fabaceae and Solanaceae family plants get leafminer infestation sooner. This includes beans, peas, tomato, potato, eggplant, etc.
Does leaf miner impact indoor plants?
Although indoor plants and plants in a greenhouse or polytunnel are safer than outdoor plants, there’s no guarantee that leafminers won’t affect them. Since there’s less contact between leaves and the insects, indoor plants are unlikely to get leafminers. But if you have houseflies or your indoor plants are near a window, you can expect to see some doodles in some leaves.
Should we remove leaves with leafminers?
Leaves affected by the leafminers don’t threaten the plant’s health. In areas with enough chlorophyll, the leaf will continue to photosynthesize. Yet, the larvae may become insects and threaten the whole cultivation area.
Thus, removing the infested leaves would benefit the plant in the long run. Disinfecting the area on site is a must, especially if you’re growing in a controlled environment such as a greenhouse.
Leaves removed from the plant this way mustn’t be put in your compost bin. The larvae can still live, thrive inside, and potentially breed more of them. The best way to dispose of them is to disinfect and bury them. But before them, let’s talk about prevention and leaf miner disinfectants.
Seedlings getting leafminer is the critical problem. Removing a leaf from the seedling would dramatically alter the plant’s growth, and it can even be fatal. You may want to destroy the whole seedling to save the rest.
How to prevent leafminers?
As we know, leafminers are the larvae of insects like flies and beetles. The best way to prevent leafminers is to make the environment uncomfortable for these insects.
1. Physical barriers
Physical barriers, such as net houses, could significantly reduce the chances of leafminer attack. You can also build a greenhouse or a polytunnel if you need more climate control. Cover the sides of the tunnel with an insect net.
Most people have their nurseries separately, and some also have indoor nurseries. You may have to cover the seedlings with mesh if your nursery is in a different area. This will prevent flies from coming into contact with them.
Yet, we must not install them in areas where leafminers were noticed within the last year. That’s because the pupae would still survive in the cultivation area. The barrier has no use when they are inside.
2. Install insect traps
Flytraps are instrumental in controlling leafminers. Use one of those electric flycatchers if you are a small-scale grower or have an indoor nursery. Every fly caught has a significant impact on the overall health of your garden.
Such products would not be viable for industrial-scale farms. Instead, you can try building a trap yourself.
Some farmers use a grease trap. Grease is spread on a yellow polythene. This is now installed like a fence in the garden. Flys are attracted to the yellow color. They stick with the grease when they come in contact with the polythene.
3. Keep your garden clean and simple.
A crucial step is to remove weeds like lambsquarter, which serve as a food source for these pests. By eliminating these weeds, you reduce the likelihood of leafminer infestations. Also, monitoring your plants and promptly removing and destroying any leaves showing early signs of damage is essential. This prevents the problem from spreading.
How to treat leafminers
No one has 100% control over the garden. Some insects can still sneak in and create leafminers. As gardeners, we must be prepared to handle such situations, too.
When leafminer infestation happens, the first thing to do is remove the leaves from the plant. This would prevent the larvae from developing into a pupa and further infestation on the same or nearby plants. If it’s in your nursery, you may have to remove the infected seedling to prevent other seedlings from getting it. Sometimes, on plants, you may remove an entire branch.
Once you remove them, you have to destroy them properly. You may have to treat the scrap leaves and branches with pyrethrin. Do not compost leafminer-infested leaves because the larvae and pupae can thrive there.
You can then treat your garden with pyrethrin to avoid any remaining infestation. This would also ensure insects are not around to lay more eggs. Yet, the effect of pyrethrin lasts only a week. Hence, you may have to treat your garden with pyrethrin every seven days for at least a month.
Another pesticide you can use instead of Pyrathrin is Spinosad. Spinosad is a naturally occurring insecticide classified as a macrolide. It is produced through the aerobic fermentation of the soil bacterium Saccharopolyspora spinosa, first isolated from soil samples. This fermentation process results in a compound effective against various insect pests, making it widely used in agricultural and horticultural applications for its environmentally friendly properties.
Lastly, Neem oil does give similar results. Compared to other pesticides, I love using neem oil because it’s a plant extract. It’s organic and has been used since ancient times.
Important Notice: Any reference to a pesticide or its label is intended for educational purposes only. Always adhere to the directions provided on the pesticide container’s label. Ensure the plant you intend to treat is specified on the pesticide’s label. Additionally, observe the required interval between pesticide application and crop harvest. Remember, the label instructions are legally binding.
