Tony O’Neill, gardener and author of the popular “Composting Masterclass” and “Your First Vegetable Garden,” combines lifelong passion and expert knowledge to simplify the art of gardening. His mission? Helping you cultivate a thriving garden. More on Tony O’Neill
Occasionally, when I step into my garden to take care of it, I see tiny marks on some of my plants, on the leaves mostly. At first, I didn’t realize what was happening, but when I found out what was causing it, I made sure to take some steps which I found compelling. The allium leaf miner is a pesky insect that takes up residence around your plants, shredding anything in the allium family.
How to control allium leaf miners? The only surefire way to prevent allium leaf miners is to cover the plants before they are affected. Enviromesh, insect mesh, or even fleece can be used extensively. Prevention is much better than cure. If crops have allium leaf miners, the safest bet is to burn and destroy the plant to prevent its spread.
There are several ways to get rid of and control allium leaf miners. You may find the best application you want to mix and use some of these methods together. Applying the techniques below regularly will ensure you do not get an infestation of allium leaf miners.
The best method(s) to use may also depend on the size of the garden and the location of the garden. In this post, I aim to provide information about allium leaf miners and give you more options for tackling this garden pest.
What are Allium leaf miners?
The Allium Leaf Miner is a tiny insect of the taxonomic family of leaf-mining flies. Leaf-mining insects are usually small, and the larvae cause the most considerable damage. They damage plants by tunneling through the inner leaves, eating the internal tissue in their way. This causes several negative situations for the leaves.
As stated, they are tiny insects, so there may be difficulty in identifying them, but don’t worry; this post will show you how you may do that. During the larval phase, they can reach a length of one-third of an inch.
Adults are only about one-tenth of an inch long. Don’t be mistaken, though; just because they are small does not mean they cannot cause severe damage to your plants. These pests can ruin crops of onions, garlic, leeks, and other alliums.
Allium leaf miner is similar to leek moth, as it causes substantial damage to Allium crops at the larval stage. Larvae mine into the leaves, stalks, onions (dry bulb, green), bulbs of leeks, garlic, shallots, and chives. As they grow, larvae move towards the bulb and sheath leaves.
What are Alliums
Allium is a genus with 600-920 species, making it one of the largest plant genera in the world. Allium, or flowering onion, is a spectacular and unusual-looking bulb beautifies any garden. As the name suggests, allium plants are members of the Allium family and include onions, leeks, garlic, and chives.
Allium leaves tend to be long and strappy. Most early-blooming alliums have foliage that grows to die early as the plants go dormant for the summer. The flowers form clusters and are usually round but can also be star-shaped or cup-shaped. Alliums are low maintenance. They will need regular water.
Most Alliums are bulb-forming except Allium schoenoprasum (common chive), which grows from rhizomes. Some common alliums include:
- Allium forrestii
- Allium ‘Mars’
- Allium ‘Purple Sensation
- Allium ‘Dready’
- Allium falcifolium
- Allium amphibolum
- Allium ‘Purple Caila’
- Allium ‘Red Mohican’
- Allium rosenbachianum ‘Album’
- Allium ‘Purple Rain’
Identification of Allium Leaf Miner
The Allium Leaf Miners are very small, as we now know. So you may not be able to notice them. You can, however, notice signs of damage that appear on the leaves. They attack leeks, onions, shallots, and other onion family members.
Adult allium leaf miners are less than 3 millimeters (mm) long. They are grey or black, have a distinctive yellow or orange patch on the top and front of their heads, and have yellow “knees.” Yellow also can be seen on the sides of the adult fly’s abdomen, and the wings are situated horizontally over the stomach when at rest.
The eggs are white, tiny (only 1/2 mm long), and slightly curved. The larvae are white, cream, or yellowish, are headless, and can reach 8 mm long at their final instar. The pupae are dark brown, 3.5 mm long, with posterior spiracles of 18 to 20 bulbs per spiracle.
Since they are so tiny and difficult to see, it’s easier to identify the damage they do to your crop. As the insects feed on the leaves, they become wavy or shrunken. This is similar to the damage caused by using a sprayer previously used to spray herbicides.
Symptoms of Allium Leaf Miner
For the symptoms, certain stages depend on the growth of the insects. The adult fly initiates infestations. Before laying eggs, the female flies feed by making punctures in the leaves and sucking up the exuding sap, which causes distinctive lines of white dots on the foliage.
After the adult flies do the initial damage, the subsequent injury is caused by the maggots (larvae) and the pupae. The larvae are white, headless maggots without legs. They make tunnels in their host plants’ foliage, stems, and bulbs. The cylindrical brown pupae are about 3mm long and embedded in the stems and bulbs.
The first problem you most likely will notice is that the leaves become distorted, start dying, and no longer grow normally straight and upwards; some leaves will lie on the ground.
Another worthy thing to note is that the leaves have minor, light green/grey marks in rows down the foliage – these are the points at which the fly stage of this pest feed on the sap.
The most obvious signs of a problem appear when the plants start rotting. Plants affected by allium leaf miners tend to deteriorate due to secondary infections from fungi and bacteria that develop in the damaged tissues.
Allium leaf-mining fly lifecycle
The cycle of this insect is unique because of how they affect the plant and use it to feed its growth. The process is as follows:
- Male flies fertilize females. Females damage leaves to create a food source and lay their eggs. These wounds leave marks with little white dots on the leaves.
- Once these wounds are prepared on top of the leaves, the female fly lays its eggs inside the wound, where they hatch and become yellow-colored larvae.
- The larvae find their way through the leek, tunneling down to its base as they feed.
- At the end of the tunnel, the grown larvae develop more, turning into brownish-red pupae.
- The pupae mature inside the leek plant during the summer, growing into adult flies. These new flies are the ones that fly at the end of summer and in fall to breed a second cycle.
- Fall / Autumn pupae stay inside the leek over the winter and start the cycle again in spring.
- If infested plants aren’t removed and destroyed, allium leaf miners will cycle through the fertilization and laying process over and over for years.
How to control allium leaf miners
Alliums don’t attract too many pests, but they can get a few fungal diseases, like downy or powdery mildew (Check out this blog post to see how to treat this fungal disease) and rots, but these are not as much of a problem as insect pests such as the allium leaf miner.
There are no curative treatments against allium leaf-mining flies. However, it is possible to keep them from attacking your leek plants by providing adequate protection. Here are a few ways to help combat Allium leaf miner
- Net against Allium leaf miner
- Natural Predators
- Destroy Infected Plants
- Companion Planting
Catch against Allium Leaf Miner
The most effective protection is usually an anti-insect net. The most appropriate net is one with a 1/5-inch mesh at most. Position hoops so that the net does not touch any part of the leek plant.
Check that no space is more than 1/5 inch wide around the net, even near the ground. The net prevents, as much as possible, the likelihood of tiny insects reaching your plants. The net can be removed once risks of leaf-mining fly attacks are averted.
One very effective method of removing allium leaf miners is to physically remove them by hosting the leaves or plants upon which they stay. Soak them with a strong blast of water from a high-pressure hose. It’s also best to use the hose that works for high-pressure sprays.
This should be done regularly (at least once weekly) for the best results and used with other control methods. Among the benefits of this method, it is easy to do and inexpensive; however, as far as negatives, this method may not remove all allium leaf miners from the plant, and it must be repeated regularly for best results, which may make it time-consuming.
As I illustrated in an earlier post on whiteflies (Click Here To Read), insects such as parasitic wasps, ladybug beetles, and predatory mites are all predators of pest insects. They feed on more minor pests and destroy nymphs and pupae. A single female wasp can kill many problems over her 12-day lifespan, making them effective in targeting allium leaf miners.
Among the benefits, it is a sustainable, natural, non-toxic means of biocontrol. Using natural predators is easy to implement, cost-effective, and effective in killing large numbers of allium leaf miners.
The major disadvantage of this method is that if the natural predators are not released at an optimal time and in sufficient quantities, it may lead to another infestation with another set of issues. There are many reasons to introduce beneficial bugs to your garden. Over the long term, they are safer and more effective than chemicals.
Destroy infected plants
Destroy infested leek plants: I recommend getting rid of all infested plants in a worst-case scenario. Do not compost them because the pupae could move out and into the compost, rendering them unusable. Do not put into the green waste recycling for the same reason.
Even though this process would kill off this pest, it could spread while waiting for collection. The safest bet is to burn the affected plants right away. This will destroy the problem and prevent any further issues.
You may want to consider having some plants which have beneficial properties in that they repel leaf-mining flies. Companion planting your alliums within these other plant species can help ward off the pests completely. Plants ideal for companion planting with alliums are mint, lemon balm, or common rue.
As of today, there are no effective insecticides against allium leaf miners. However, a short-lived natural pesticide may be helpful by damaging the outer layer of soft-bodied insect pests, causing dehydration and death within hours. But this is ineffective, so you must get prevention first and last.
Two products on the market can help with Allium Leaf Miner. These are as follows.
- Organic Neem Oil
- SB Plant Invigorator
Organic Neem Oil
Neem oil is an effective DIY method to control Allium leaf miners in the garden. It can be sprayed on plants to kill eggs, larvae, and adults. Mixing about 1 oz/ gallon of water and spraying all leaf surfaces (including the undersides of leaves) until completely wet may prove effective against larvae, stifling their development and killing them before adulthood.
Also, it may act as a repellent, preventing adult Allium leaf miners from landing on plants or laying their eggs on the leaves. Because of the nature of this oil being natural, it is non-toxic, biodegradable and environmentally friendly. They can also be used on edible plants and house plants.
They are cost-effective and easy to use. However, they only kill when applied directly, must be reapplied regularly, and are time-consuming. Neem oil can be created by mixing:
- 1/2 tsp of organic neem oil concentrate
- 1 tsp of mild liquid soap
- 1 liter of tepid water
SB Plant Invigorator
This soap-based solution is another organic compound designed by a commercial tomato grower fed up with pests eating his tomatoes but wanted to remain organic.
It was designed to work by dehydrating pests’ larvae and pupae stages when soft-bodied. It also coats them in a film that prevents them from breathing. Again like Neem, it is essential to catch the cycle early to use either of these products. If you want to see how these two products are used, check the video below.
Something that can help reduce the adult population is sticky yellow insect traps. These are placed between 1ft from the soil surface and 1ft below the head of the plants. These work as the adults are attracted to the bright yellow color and stick to the card.
These will not cure an infestation but can reduce adult numbers drastically and are cheap to buy on Amazon. So are worthy of adding to your prevention regime.
In the case of transplants, check for signs of leaf miner damage before planting, then remove plants from the soil immediately after harvest.
It’s best to prevent any need to use pest control in the first place by starting with healthy fertile soil, matching your plants to the soil type, ensuring proper sunlight levels and watering conditions, and using appropriate organic fertilization and pruning when necessary. Follow these six rules to ensure a pest-free garden.
Build Healthy Soil
The healthier the soil, the better plants can withstand pest attacks. Building healthy, fertile, living soil is essential to preventing pest problems. Organic matter is vital in building soil, but more on that as we continue.
Limiting Soil Disturbance
Research suggests that routinely turning the soil has various drawbacks. It leaves the soil surface bare, causes soil compaction, encourages runoff and erosion, and harms soil microbes and earthworms.
This is why no-dig is such a great gardening concept. I use the no-dig approach in most of my gardens. The soil web of life is essential; each time you dig in that soil, you are destroying the soil life, which can take years to repair itself.
Have you ever dug over some ground and just left it unattended? What happens to it? Weeds grow, right? This is because it is mother nature’s way of protecting soil life. Soil should not be bare; it should be covered at all times. But we don’t want to cover it with weeds or grass, but this is where mulch comes in.
Add two to four inches of grass clippings or mowed leaves to the garden when plants are about four inches high to reduce water evaporation, suppress weeds, moderate soil temperature, prevent soil compaction, and add slowly decomposing organic matter to the soil.
Compost is the organic matter I spoke about earlier in this article. It not only retains water in your soil but also helps it drain, adds air, and improves the structure of the soil. The other benefit is it is utilized as food for all the microbial life you want in your soil. Without it, the microbes will die.
Add one to two inches of well-decomposed compost to the garden to supplement nutrition in the soil and encourage a desirable soil structure. If you are unsure how to make compost or can not afford to buy it, check out my complete composting guide for beginners, where I show you everything you need to know to produce the best nutrient-dense compost for your garden.
Plant cover crops
Over the years, you will have heard the term green manure or cover crops. They are the same thing. As mentioned above, the ground needs to be covered when growing space is dormant; a cover crop or green manure is a perfect plant to grow.
At the end of the growing season, plant a cover crop, such as ryegrass, peas, or clover, to enhance the soil’s fertility. This will also lessen erosion over winter months, suppress weeds, and improve the soil structure.
There are so many benefits to using green manures and cover crops that I wrote a complete article explaining the benefits and what each plant species can do for your soil life. You can read that here.
I am not a firm believer in crop rotation for several reasons. The biggest is that it was a process designed during WW2 and was a way to help combat disease allowing the ground to rest. However, we have evolved in gardening and understand more about how pests and conditions work.
Understanding the nutrition of the soil life, with mulching and composting and not using chemicals on our ground, harms the soil life. The soil fertility is much improved, and so is the soil life. Looking after that soil life helps our plant’s immune systems to fend off pests and diseases.
That being said, I still think that when pests such as Allium leaf miners are in a growing bed, it may be worth removing the crop to a new location just in case your garden husbandry isn’t as good as you would like.
FAQs on How To Control Allium Leaf Miner. Protect Your Plants!
How do you control Allium leaf miners?
To control Allium leaf miners, you can employ various measures:
- Practice crop rotation to disrupt the pest’s life cycle.
- Remove and destroy infested leaves.
- Apply organic insecticides like spinosad or neem oil.
- Use floating row covers to prevent adult flies from laying eggs.
- Keep the garden clean and free from debris.
- Monitor plants regularly for early detection.
- Remember, integrated pest management techniques offer the best approach to controlling Allium leaf miners.
How do you manage and control leaf miners?
Controlling leaf miners organically involves various methods. Use floating row covers to prevent adult flies from laying eggs. Remove and destroy infested leaves. Apply neem oil or insecticidal soap. Encourage beneficial insects like parasitic wasps. Implement crop rotation and maintain plant health.
What chemicals are used to control leaf miners?
Various chemicals control leaf miners, including insecticides like spinosad, abamectin, and imidacloprid. These chemicals are applied as sprays or systemic treatments to target leaf miner larvae and disrupt their life cycle. However, following label instructions and considering non-chemical methods for sustainable pest control is essential.
Allium leaf mining is especially troublesome. They are so tiny you might not notice them, so it might not be easy to handle them, but as this post has outlined, you can see signs of allium leaf miners from the effects of their presence.
The options I have laid out can provide the most effective results for controlling allium leaf miners. You want to do everything possible to avoid getting them on your plants. Keep them out of your garden if possible.
Like with most things, it requires some effort. I believe that to control this pest more effectively, a combination of these options will provide the best possible outcome. This will enable you to handle the situation best.
Remember, it’s best to ensure you don’t need to use pest control in the first place, so try to build the soil quality enough to reduce the work you might have to do when an allium leaf miner starts showing up on your plants.
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Remember, folks, You Reap What You Sow!