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Purple Power

Pest: Leaf Miners

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Pest: Leaf Miners


(Multiple species)





Plants rarely die from leaf miner, however pathogenic fungi and bacteria may enter old mines left from eradicated insects. This can cause leaves to turn yellow and drop.


Special Species Notes


The term "leaf miner" is a common name for a type of pest that lives inside the tissue of the leaf. These bugs mine through the leaf eating the best parts, and leave a trail of damage behind. Many less-famous leafminers do not have common names.


A "leaf miner" is not actually a species of bug - it is a generic term for the larva of any bugs that live inside leaves and tunnel them to eat (including some moths, sawflies, flies and beetles). Although different types of leaf miners come from different bug parents, the leaf markings look very similar.


Found in greenhouses, home gardens and landscaped areas across the country, leafminers are the larval (maggot) stage of an insect family that feeds between the upper and lower surfaces of leaves. On heavily infested plants it is not uncommon to find 6 or more maggots per leaf.


leaf miners are protected from many predators and plant defenses by feeding within the tissues of the leaves themselves, selectively eating only the layers that have the least amount of cellulose. 








Larva of the American serpentine leafminer, Liriomyza trifolii (Burgess), in a mine in a squash (?) leaf.

Photograph by Lyle J. Buss, University of Florida.


Leafminers are the larvae of various insects including beetles, flies and moths. Larvae are usually very small, reaching between 1/5" and 1/8" in length. Only maggots are legless. Leafminer eggs can be confused with thrips eggs.


Adults (1/10 inch long) are often black to gray flies with yellow stripes and clear wings. They are similar in appearance to small, hunched-back house flies and lay their eggs on the undersides of leaves. Larvae are worm-like maggots (1/3 inch) which are often pale yellow or green in color. They create winding tunnels that are clear, except for the trail of black fecal material (frass) left behind as they feed.


Some common names: Serpentine leaf miner, pea leaf miner, South American leaf miner, South American miner fly.




Larva of the American serpentine leafminer, Liriomyza trifolii (Burgess),

exposed from a mine in a squash (?) leaf.

Photograph by Lyle J. Buss, University of Florida.



Common Species:


boxwoods, a pest that is a very small (one-eighth of an inch long) yellowish-orange mosquito-like fly whose larvae spend winter inside the infested leaf, emerging as adults in early Spring. Adult females lay their eggs inside that lush new growth.


Grapholita delineana, (caterpillar) mines leaves when young after its too big it bores into plant as known as the hemp borer.


The flea beetle grub (Phyllotreta nemorum) makes tunnels in tight spirals which end in blotches.


The Pea leaf miner (Phytomyza horticola). Maggots are greenish-white, 3-4mm long. Tunnels are short and straight. 


Agromyza reptans are similar to the pea leaf miner in size and shape, but they mine linear tunnels along leaf margins, which expand in to brown blotches, filled with frass. The flies are brownish black, legs black with yellowish tibiae and tarsi and puparia are reddish brown.


Liriomyza eupatorii- mines often in a spiral pattern, the rest of the mine is linear. Adults have black bands on their abdomens. legs are yellow, usually with brownish-black striations 1.5mm body length, wing length is 1.6-2.2mm


Liriomyza cannabis- maggots make tight spiral mines with frass scattered along the tunnels, like a string of pearls.


Liriomyza trifolii (Burgess), sometimes known as the American serpentine leafminer, readily infests greenhouses. As a vegetable pest, however, its occurrence is limited principally to tropical and subtropical regions. Expanded traffic in flower crops appears to be the basis for the expanding range of this species.


The vegetable leafminer (Liriomyze strigata)  recorded from 240 host plant genera in 35 plant families worldwide. maggots are pale, up to 2mm long. the mine slender light green serpentine tunnels that end in brown blotches. Mines begin near the leaf margin and end near the midrib. Larvae pupate externally. Adults resemble tiny houseflies- shiny black with yellow marking along the sides. , 1.7-2.1mm long. Females lay eggs near leaf edges. It is found commonly in the southern United States from Florida to California and Hawaii, and in most of Central and South America. Occasionally it is reported in more northern areas because it is transported with plant material. It cannot survive cold areas except in greenhouses.




Adult vegetable leafminer, Liriomyza sativae Blanchard.

Photograph by Lyle J. Buss, University of Florida.


Some leaf miners that attack fruit can also hit ornamental trees. Phyllonorycta corylifoliella is often seen on pears, where it produces a mined area in the middle of the leaf, but can also affect Crataegus, Corylus, sorbus and Malus.








Life cycle


leafminers are the larval stage of a variety of insects. The female adult lays its eggs inside or on the underside of the leaves. When the eggs hatch, the outside larvae tunnel into the leaves to feed for up to 3 weeks, creating the tunnel-like appearance often seen on foliage.


The leafminer is an insect of the family of the Agromyzidae, and during its life cycle it goes through several stages:


Egg: They have an average size of 0.25 mm and therefore it will be virtually impossible for you to detect them in your cannabis plants. In addition, they are inserted into the leave tissue, making it even more difficult to identify them. Mated females use their needle-like ovipositor to lay up to 250 eggs just under the surface of the leaf epidermis. Deposited eggs may appear as small raised spots on the leaf.


Larva: It is in this phase when the leafminer really damages the cannabis plants, as the eggs located inside the leaves hatch, resulting in small larvae that grow while feeding themselves and tunnelling inside the leaf. Within 10 days hatching larvae tunnel through the mid-leaf tissue, feeding as they go and leaving tell-tale wavy lines that are visible on the surface. These tunnels are visible to the human eye. Larvae mature in 2-3 weeks, and when ready to pupate, leave the leaf and drop to the soil.


Pupa: Once the larva has already developed and nurtured enough to complete this stage, it breaks the leaf and drops to the substrate. There, it buries itself about an inch to create the pupa, inside which the metamorphosis will take place. However, they can also do so on the surface or on the undersides of the leaves. Once on the ground, they dig 1-2 inches into the soil and pupate. Adults emerge within 15 days as adult.


Mature larvae overwinter in the soil under host plants. As temperatures warm in the spring larvae pass to the pupal stage and appear as young adults in late April.


Adult: The leafminer emerges from the pupa turned into a small winged insect of approximately 2 mm.


There are typically 2-3 generations in a season, depending on weather and climate for outdoors. In greenhouse there are multiple generations, year round.



Host plants:


Some larvae may create a mottled look from their feeding. When the larvae are done feeding and are ready to pupate, they eat their way out of the leaves and drop to the ground to pupate. Some however will pupate within the leaf when it has finished feeding.


Damage can be limited in initial stages of infestations but increase as leafminer numbers multiply, and even minor infestations, while not killing a plant, will cripple its hardiness. Leafminers are a major cause of poor harvest numbers in home gardens as they weaken individual vegetable plants. They’re especially fond of spinach leaves and their tunneling severely decreases the attractiveness and value of the crop.


Various types of leafminers attack various kinds of plants. They’re found on broadleaf trees, including elm, aspen, hawthorn, poplar, birches, Norway maple, sycamore, arborvitae and junipers as well as shrubs and bushes, including lilacs.. These larvae are found throughout North America.


Chrysanthemum, gerbera, gypsophila, and marigold, Numerous broad-leaved weed species, Solanum americanum; Spanish needles, Bidens alba; and pilewort, Erechtites hieracifolia


Aubergine, beet,. red pepper, celery, chrysanthemum, carrot, cucumber, faba bean, eggplant, garlic, hemp, lettuce, lucerne, melon, onion, pea, common bean, potato, radish, tomato, spinach, blackberries, cabbage, peppers, citrus plants, squash




First signs:




They bore into the leaf and “mine” the inside, leaving patches of infected areas between the ribs and they do look a lot like small maggots. The mine becomes noticeable about three to four days after oviposition and becomes larger in size as the larva matures.


The damage produced by the leafminer larvae can be easily identified: Squiggly gray or brown or translucent lines on leaves. the lines (also known as mine or tunnel) can be linear, serpentine, or blotch-like. Most appear on top side of leaf. These small tunnels damage the plant and prevent the proper development of its metabolic functions: in their path, the larvae devour part of tissue the plant uses to do photosynthesis. As a result, the leaves go partially or totally dry and the productivity of the plant decreases.

Presence of flies, beetles or butterfly/moth


Eggs on leaf underside or punctures in the leaf. The punctures that the leafminer females make on the leaves. They make them for two reasons, either to feed themselves from the lifeblood of the plant or to lay their eggs inside its leaves.



Extensive mining also causes premature leaf drop/death

Dry patches on leaf






What to do For preventative use


Remove and discard any leaves that show signs of leaf miner worm damage, as their tiny eggs and larvae are difficult to see. This will prevent future outbreaks. Another great option is to use predator nematodes, They will hunt and kill your leaf miners even within the leaves


one of the best ways to truly rid yourself of them is to physically crush them within the leaf. This will not be difficult to perform because they are trapped inside the leaves.


Floating row covers


Yellow and blue Sticky traps. There are plastic, double-sided adhesive strips which are useful to trap adult individuals.




For indoors, temperature and humidity are two decisive factors for the development of a leafminer population. High humidity and warm temperatures are ideal conditions for their appearance. If you want to avoid this pest as well as any kind of fungi, its recommended keeping humidity levels under control.


Greenhouse cultivation, placing anti-insect meshes can help prevent the pest from entering.


In outdoor cultivation, it becomes much more difficult, which under the right weather conditions can become a serious problem.


Neem oil can be a good ally to prevent leafminer. It will leave an unpleasant taste/smell on buds when used to treat flowering plants.


Spinosad is an organic insecticide made from the fermentation of a specific soil bacteria (actinomycete Saccharopolyspora spinosa) and kills leaf miners via ingestion or contact by affecting the insect's nervous system. Spinosad can be a good choice for organic and outdoor growers, because it is very toxic to leaf miners, but is less toxic to many beneficial insects, bug predators and spiders. Spinosad products can be used directly to kill leaf miners by ingestion and should be sprayed liberally anywhere you see leaf miner damage. Although depending on what your "parent" bug is, Spinosad may not be as effective as other treatments, it does work and it's very safe for plants, animals


Note: Most spinosad products are effective for only about 24 hours after being mixed with water, so only mix as much as you will need per application. Anything left over will be waste. 


BT - for moth or caterpillars. Some types of moths lays eggs that hatch into leaf-tunneling larva before turning into caterpillars and eventually becoming a moth. If you see evidence of moths or caterpillars on your plants (for example something is also munching on your leaves, you see little black droppings, or you catch a worm in the act) in conjunction with leaf miner damage, get BT spray immediately.


This biological insecticide contains the bacillus thuringiensis (BT) bacteria which kills larva and prevents caterpillars from being able to eat. This is one of the most effective ways to kill caterpillars and larva without hurting beneficial insects. As a bonus, it also kills other cannabis pests like fungus gnats and worms. Make sure to thoroughly mist both the tops and bottoms of leaves, and apply again after a heavy rain (since that will wash the BT away). Since BT is harmless to humans, you can use BT products up to the day of harvest. BT spray almost instantly stops caterpillars from being able to eat, but doesn't kill them directly. So although you may see the caterpillars alive and apparently unharmed after spraying, the BT is still doing its dirty work.


If the BT spray has no effect after a couple of days, it's a big sign this could be a different type of bug as BT spray is very effective at killing young caterpillars and moth larva.


If it does seem to help, repeat your treatment every week for as long as you're still seeing caterpillars or leaf miner damage (though you can give BT more often if there's a heavy infestation).


Azatrol EC contains azadirachtin, the key insecticidal ingredient found in neem oil. This concentrated spray disrupts growth and development of pest insects and has repellent and anti-feedant properties. Best of all, it’s non-toxic to honey bees and many other beneficial insects.







Pesticides won’t work against leafminers, simply because they are protected by the plant’s own skin. Your best bet is, therefore, to simply squish the little maggots within their burrow, then remove the leaves that were affected.







Biological control

There are several types of parasitoid that attack leaf miners: parasitic wasps Dacnusa sibirica, Diglyphus isaea and Opius pallipes.There is a type of parasitic wasp known as Diglyphus isaea which is a parasite to leafminers and will happily kill them. They can be ordered online if you want to help reduce leaf miner numbers with nature's pesticide.  adults are 2 – 3 mm long, metallic green, with short antennae. The other stages are not seen as they are in the mine of the leafminer. Two weeks after introduction it is possible to see parasitization by short or stopped mines containing dead larva. The pupae of the parasite can be seen by holding the leaf up to the light.


Parasitic Chalcid wasps and parasitic wasp braconid (Liriomyza larva) feeds on leaf miners










Steinernema carpocapsae- a soil nematode that can be sprayed on foliage at night. Some leaf miners palpate in the soil.







The link below will take you to "An Intro to benefical bugs and beneficial insect food" it has a list (been worked on) to pests and beneficial insects





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