The tomato leaf miner is an insect that arrived in our regions a few years ago, directly from South America. Also known as the leaf miner or moth, but commonly referred to as the tomato pinworm, it is perhaps the most devastating among the pests and diseases affecting this plant. The damage caused by the tomato leaf miner to crops is very severe. Despite this, it is difficult to find information about effective natural remedies. For this reason, we have decided to share some specific organic remedies against the tomato disease caused by this moth.
In this article, we will describe in detail the procedures for biological control of the tomato leaf miner. So, if your cultivation is affected by it, you won’t have to turn to multinational companies to buy chemical pesticides. The chemical solution is often presented as the only way to solve the problem, but we will show you that it is not the case. The remedies we are about to illustrate will keep your crop entirely organic and healthy from every perspective, especially by preventing poisoned food from reaching your (our) tables.
Fighting the Tomato Leaf Miner
First of all, we wonder how it is possible for the tomato leaf miner (and other insect species) to arrive from its peaceful ecosystem in South America and cause damage to our crops and ecosystems, which are not accustomed to the presence of this insect.
A plausible answer could be international trade and the Western practice of importing fruits and vegetables that can be easily cultivated on our farms. Importing these goods also brings unwanted guests that alter our ecosystem. There are also darker theories on this subject, but let’s put aside these controversies and simply try to understand how to contain the tomato leaf miner without using pesticides.
Spread of the Tomato Leaf Miner
The tomato leafminer-Tuta absoluta
The tomato leaf miner is a moth, belonging to the family of gelechiids. The moth was already known and widespread throughout the South American continent, except for the mountainous areas of the Andes. It appeared in Europe for the first time in Spain in 2006. It is believed to have arrived in the old continent through the commercial exchange of tomatoes infested with the insect. In Italy, it first appeared in Calabria in 2008. At first, it affected only greenhouse tomato crops, but later spread rapidly to all southern regions. Today, it is also present in central and northern Italy, but fortunately, the harsher climate in the north has limited its development.
Tomato Leaf Miner: Appearance and Characteristics
Tomato leafminer (Tuta absoluta) larva
The tomato leaf miner is a small silvery-gray moth that affects tomato plants, measuring about 6-7 mm in length. It has black streaks on its wings and very small antennae.
The female can lay up to 200 eggs per day on the upper side of leaves, on both green and ripe fruits, and other parts of the plant; the eggs hatch into larvae, which reach a length of 7-8 mm when fully developed.
The young larvae burrow into leaves, stems, and fruits, creating galleries, hence the name “leaf miners.” Inside these galleries, they find shelter and complete their development. Once fully developed, the moth larvae pupate in leaves or underground, giving rise to a new generation of moths.
The life cycle of the tomato leaf miner can last from 25 to 75 days, depending on the climate. The female moth lives about two weeks longer than the male.
Let’s now move on to the damage caused by the larvae to tomato plants.
Damage to Crops
The affected fruits show necrosis at the calyx or exit holes on the surface. Moreover, they rot inside in the affected area, making them unsuitable for sale or consumption.
In cases of heavy infestation, the crop loss can reach up to 70%, and in some instances, production losses of 100% have been recorded. It’s truly a scourge considering that up to 10-12 generations of moths can occur in a single year.
Biological Defense Strategy against Tomato Leaf Miner
First of all, let’s clarify that to protect our crops from the Tomato Leaf Miner, we cannot rely on a single approach. Instead, we need to implement an integrated strategy, starting with the correct cultivation of tomato plants.
Firstly, during the winter season, it is necessary to work the soil thoroughly and deeply. This allows for the vigorous development of tomatoes, whose roots need plenty of air and space for propagation. Additionally, by doing so, we reduce the number of overwintering pupae of the Tomato Leaf Miner, which would otherwise reproduce easily in spring.
Secondly, excellent mulching and weed control are essential. This is not only within the cultivation area but also in the surrounding zones. The Tomato Leaf Miner thrives in tall grasses, especially grass species. It hides there during the day and reproduces and lays eggs at night.
Crop rotation and the removal of potentially infested plants after harvest are also crucial. A cost-effective and quick method for disposal is burning, where it is allowed by the modifications to the Legislative Decree 152 of April 3, 2006. Always make sure to follow all necessary procedures for burning and be careful not to cause any damage.
Defense Techniques
After this important premise, let’s look specifically at the biological defense techniques against the Tomato Leaf Miner (which, by the way, are also the most effective and economical to implement).
One of the characteristics of this notorious moth is its ability to absorb and resist the phytotoxicity of pesticides. Due to this ability, combating the Tomato Leaf Miner is becoming increasingly challenging. The only way to contain the spread of the moth is through mass trapping, which can be done in three different ways.
Pheromone Traps
DIY pheromone trap
The pheromone trap involves setting up traps with a sexually attractive pheromone at the center. The pheromone attracts the male Tomato Leaf Miner, which becomes trapped and unable to reproduce. These traps can be homemade. In the image above, we used a cut plastic container with a wire passing through the ends. The small pheromone is placed at the center of the wire.
Water and oil are poured inside the container (you can use kitchen waste oil). The oil creates a film on the surface, where the moth gets trapped without the ability to fly again. If you want to try building this trap, you can find the pheromone online at this link.
This trap serves two purposes. First, it acts as monitoring to check for the presence of the Tomato Leaf Miner. Additionally, if placed with enough density, it can initiate mass capture of the moths.
It is advisable to position the traps at the outer edges of the cultivation area, with one trap for every 50-75 square meters. The effectiveness of the pheromone diminishes after a month, so it will need replacement.
In the case of frequent rainfall, you can use a different type of trap. Simply use a bucket with a lid (similar to a paint bucket). Create an opening in the lid to prevent wetting the pheromone or needing to move it.
Ready-made traps can also be found online. Here is an example of a ready-made trap. However, in all honesty, the handmade solution is preferable in terms of cost-effectiveness.
Chromotropic Traps
The second method for implementing biological defense against the Tomato Leaf Miner is the chromotropic trap. This trap is based on a simple principle: our beloved moths (as well as many other flying insects) are attracted to certain colors. This way, we can lure them to the trap, coated with a special adhesive. Once they land on the trap, the Tomato Leaf Miner remains stuck, again without the ability to escape. The color used for the Tomato Leaf Miner is yellow, but blue traps are also used in organic agriculture.
Chromotropic trap
You can find a good set of ready-to-use traps at this link. Alternatively, you can opt for a homemade solution using colored plates and vinavyl glue. However, the professional solution is more reliable.
Chromotropic traps, which are not only useful for the Tomato Leaf Miner but also for other flying pests like whiteflies or olive flies, should be placed above the height of the crop, with the frequency varying depending on the size of your garden. One trap every 5-10 square meters is a good solution.
Chromotropic traps can also be entirely natural, using brightly colored and attractive flowers. Sunflowers are a good example, as they naturally attract moths and keep them away from our tomato plants. Placing sunflowers at the outskirts of the field can create a protective barrier for our tomato plants.
Electroluminescent Traps
Electroluminescence trap
The last type of trap for mass capturing the Tomato Leaf Miner is the electroluminescent trap. It is better known as an outdoor mosquito trap that you can purchase at this link.
This trap, when activated at night, irresistibly attracts the moth, presumably the female, and electrocutes it.
A 40-watt lamp can cover a reasonably large area, about 150-200 square meters. One should be more than sufficient for your home garden. To apply this technique, it is necessary to have access to a power source.
Cleaning of Infested Plants
This last technique is purely technical and agronomic. When you are inspecting your plants, pay attention to suspicious presence on the leaves, such as strange white spots, where Tomato Leaf Miner larvae proliferate.
If you notice leaves affected by the Tomato Leaf Miner, cut and remove them. This way, you minimize damage to the plant and prevent it from being attacked by a moth that escaped the other traps. It’s a simple cleaning operation that can make a difference.
When these four biological defense techniques are implemented together, they should provide adequate protection against this dreaded insect. It is important to note that the most significant damage is caused by the Tomato Leaf Miner on tomatoes grown in greenhouses. However, during hot and humid seasons, even outdoor crops can be affected by the pest.
Defense Using Permitted Synthetic Products in Organic Agriculture
For completeness, we should also mention a product widely used in recent years in organic agriculture: Bacillus thuringiensis. It is essentially a soil-dwelling spore-forming bacterium.
When ingested through contaminated plants, the bacterium sporulates in the host, releasing toxins called Bt toxins or more precisely delta-endotoxins (harmless to humans), which damage the digestive tract of Dipteran larvae (such as mosquitoes) and cause a paralytic disease in caterpillars of many Lepidoptera (like the Tomato Leaf Miner). This bacterium, particularly the kurstaki variety, is synthesized into granular powder. It is sold as a product for the biological control of Tomato Leaf Miner larvae and other dangerous insects (such as pine processionary, Colorado potato beetle etc). All of this without producing toxicity for humans, which is why it can be classified as an organic insecticide.
Now, the ethical problem is not so much related to the use of the product itself but rather to the fact that it is produced by pharmaceutical companies that also produce toxic pesticides for humans and the environment. It raises the question of whether organic farming could also fall into the trap of submission to large multinational corporations, as we have seen in traditional agriculture for decades now. Therefore, we won’t discuss other products of this kind since the wider use of another permitted active ingredient in organic agriculture, Spinosad, is now almost exclusively the domain of a well-known multinational company.
This link for the sale that we’re sharing refers to an Italian company in the sector.
Further Reading
- Leafminers / Tomato / Agriculture: Pest Management – UC IPM from University of California Agriculture and Natural Resources: This resource discusses the management of leafminers, which are normally a pest of late summer tomatoes and can reach high numbers. The most important aspect of leafminer management is conservation.
- Leaf Miner – Aggie Horticulture from Texas A&M University: This resource describes the symptoms of leaf miner infestations. Leaf miner larvae tunnel through the lamina of the tomato leaf eating the chlorophyll-rich mesophyll cells as they go, leaving an irregular pattern.
- South American Tomato Leafminer, Tuta absoluta from University of California, Davis: This resource discusses the South American tomato leafminer, Tuta absoluta, which is a serious and devastating pest of tomatoes.
