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 realise what was happening, but when I found out what was causing it, I made sure to take some steps which I found effective. Just to be clear, it was the allium leaf miner, a pesky insect that takes up residence around your plants, shredding anything in the allium family.
How to control allium leaf miner? The only surefire way to control allium leaf miner is to cover the plants before they are affected. Enviromesh, insect mesh or even fleece can be used with great effect. Prevention is much better than cure. If crops do have allium leaf miner the safest bet is to burn and destroy the plant to prevent its spread.
There are a number of ways to get rid of and control allium leaf miner. You may find the best application you will want to mix and use some of these methods together. Applying the methods below regularly will ensure you do not get an infestation of allium leaf miner.
The best method(s) to use may also depend on the size of the garden, the location of the garden. In this post, I aim to provide you with information about allium leaf miner and give you more options in being able to tackle this garden pest
What are Allium leaf miners
The Allium Leaf Miner is a small insect of the taxonomic family of leaf-mining flies. Leaf mining insects usually are very small in size, and the larvae cause the most considerable damage. They damage plants by tunnelling through the inner leaves, eating the internal tissue that stands in their way. This causes several negative situations for the leaves.
As stated, they are tiny insects, and so there may be difficulty in identifying them, but don’t worry, this post will show you just 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 a substantial amount of 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, also known as flowering onion, is a spectacular and unusual looking flowering bulb that will beautify any garden. As the name suggests, allium plants are members of the Allium family and include such plants as onions, leeks, garlic, and chives.
Allium leaves tend to be long and strappy. Most early blooming alliums have foliage that tends to die-back early, as the plants go dormant for the summer. The flowers form in clusters and are usually round, but they can also be star-shaped, or cup-shaped. Alliums are very low maintenance. They will need regular water.
Most of the Alliums are bulb-forming except Allium schoenoprasum (common chive) that 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 which appears on the leaves. They attack leeks, onions, shallots and other members of the onion family.
Adult allium leaf miners are less than 3 millimetres (mm) in length. They are grey or black in colour, 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 abdomen when at rest.
The eggs are white, tiny (only 1/2 mm long), and slightly curved. The larvae are white, cream, or yellowish in colour, are headless, and can reach 8 mm long at their final instar. The pupae are dark brown, 3.5 mm long, with a pair of posterior spiracles which can have up to 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 that has previously been used to spray herbicides.
Symptoms of Allium Leaf Miner
For the symptoms, there are certain stages depending on the growth of the insects. Infestations are initiated by the adult fly. 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 next damage is caused by the maggots (larvae) and the pupae. The larvae are white, headless maggots without legs. They make tunnels in the foliage, stems and bulbs of their host plants. The cylindrical brown pupae are about 3mm long and found 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 in the normal straight and upwards manner, some leaves will lie on the ground.
Another worthy thing to note is that the leaves have small, light green/grey marks on it in rows down the foliage – these are the points at which the fly stage of this pest fed on the sap.
The most obvious signs of a problem appear when the plants start rotting. Plants affected by allium leaf miner tend to rot 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 the plant to feed their own 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-coloured larvae.
- The larvae find their way through the leek, tunnelling down to its base as they feed.
- At the end of the tunnel, the grown larvae then develop more, turning into brownish-red pupae.
- The pupae mature inside the leek plant during the summer growing to become 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 miner 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
Net 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 in such a way that the net does not touch any part of the leek plant.
Check that there is no single space more than 1/5-inch-wide all around the net, even near the ground. The net prevents as much as possible, the likelihood of tiny insects reaching your plants. Once risks of leaf-mining fly attacks are averted, the net can be removed.
One very effective method of getting rid of allium leaf miners is to physically remove them, by hosing 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 a week) for the best results and used together 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.
Just as I had illustrated in an earlier post on whiteflies, (Click Here To Read) insects such as parasitic wasps, ladybug beetles, and predatory mites are all predators to pest insects. They feed on all sorts of smaller pests and destroy nymphs and pupae. A single female wasp can kill a high number of pests over her 12-day lifespan, making them effective in targeting allium leaf miner.
Among the benefits, it is a sustainable, natural, non-toxic means of biocontrol. The use of natural predators is easy to implement, it is also cost-effective, and is an effective way to kill large numbers of allium leaf miners.
The major disadvantage with 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 also 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 and render it 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 pest and prevent any further issues
You may want to consider having some plants which have beneficial properties, in that they repel leaf-mining flies. By companion planting your alliums within these other plant species it can help ward off the pests completely. Plants that are ideal for companion planting with alliums are mint, lemon balm or common rue.
As of today, there are no effective insecticides against allium leaf miner. A short-lived natural pesticide may, however, be useful by damaging the outer layer of soft-bodied insect pests, causing dehydration and death within hours. But this is not that effective so it is imperative that you get prevention right first as last.
There are two products on the market that 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. By mixing about 1 oz/ gallon of water and spraying all leaf surfaces (including the undersides of leaves) until completely wet, this may prove effective against larvae, stifling their development and killing them before they reach adulthood.
Also, it may act as a repellent, preventing adult Allium leaf miner from landing on plants or laying their eggs on the leaves. Because of the nature of this oil being natural, they are non-toxic biodegradable and environmentally friendly. They can also be used on edible plants and house plants.
They are cost-effective and are easy to use. However, they only kill when applied directly, must be reapplied regularly, and are therefore time-consuming. Neem oil can be created by mixing:
- 1/2 tsp of organic neem oil concentrate
- 1 tsp of mild liquid soap
- 1 litre of tepid water
SB Plant Invigorator
This soap-based solution is another organic compound that was designed by a commercial tomato grower who was fed up of pests eating his tomatoes but wanted to remain organic.
It was designed to work by dehydrating the larvae and pupae stages of pests when they are soft-bodied. It also coats them in a film that prevents them breathing. Again like Neem, it is important to catch the cycle early to use either of these products. If you would like to see how these two products are used, then check the video below out
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 colour and they 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 prior to planting, then remove plants from the soil immediately after harvest
It’s best to make sure 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 6 rules to ensure a pest-free garden
Build Healthy Soil
The healthier the soil, the better plants are able to withstand pest attacks. Building healthy, fertile, living soil is the most important way to prevent pest problems. Organic matter is so important 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 on most of my garden. The soil web of life is so important, and each time you dig in that soil you are destroying the soil life and it 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? The reason for this is that is mother natures way of protecting the 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 that I was speaking about earlier in this article. It not only retains water in your soil, It helps it to 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 not sure how to make compost or you can not afford to buy it in, then 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 either heard the term green manure or cover crops. They are basically the same thing. As mentioned above,, the ground needs to be covered at all times when growing space is dormant, a cover crop or green manure is a perfect plant to grow.
At the end of the growing season, to enhance the soil’s fertility, plant a cover crop, such as ryegrass, peas, or clover. This will also lessen erosion over winter months, suppress weeds, and improve the soil structure.
There are so many benefits for using green manures and cover crops that I wrote a complete article on them, explaining the benefits and what each plant species can do for you soil life. You can read that here.
I am not a firm believer in crop rotation for a number of 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, over the years we have evolved in gardening and we understand a lot more about how pests and disease work now
With understanding nutrition of the soil life, with mulching and composting and not using chemicals on our ground which harms the soil life. The soil fertility is much improved and so is the soil life. By looking after that soil life it helps our plants immune systems to fend off pest and diseases.
That being said I still think that when pest such as Allium leaf miner 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.
Allium leaf miner is especially troublesome. They are so tiny, you might not actually notice them, so it might be difficult to handle them, but as this post has outlined, you can notice signs of allium leaf miner from the effects of their presence
The options I have laid out can provide the most effective results for controlling allium leaf miner. You want to do everything you can 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 in order to more effectively control this pest a combination of these options will provide the best possible outcome. This will enable you to best control the situation.
Remember, it’s best to make sure you don’t have any need to use pest control in the first place, so try to build the soil quality enough to reduce the amount of work you might have to do when allium leaf miner starts showing up on your plants.
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Remember folks; You Reap What You Sow!