Citrus Leafminer: How to Identify and Control Those Squiggly Trails on Citrus Leaves

By Richard Flowers, ACCNP, Green Thumb Nursery, Ventura

Almost every day, someone brings me a handful of citrus leaves covered in squiggly silver lines, the leaves curled and distorted, and asks what is wrong and how to cure it. The culprit is almost always the same: citrus leafminer. The good news, and it surprises most people, is that on an established citrus tree the best treatment is usually to do nothing at all. Here is how to identify citrus leafminer, understand what it is doing, and decide whether your tree actually needs any help.

What Is Citrus Leafminer?

Citrus leafminer (Phyllocnistis citrella) is the larva of a very small, light-colored moth, less than a quarter inch long, that was first found in California in 2000 and is native to Asia. The adult moth does not damage plants and lives only a week or two; it is the larval stage that causes the trouble. The female lays tiny eggs on fresh citrus leaves, and when a larva hatches it tunnels, or “mines,” just beneath the surface of the leaf, feeding as it goes (UC IPM). Importantly, it can only survive in the tender, young, shiny flush of new growth; older leaves that have hardened off are not susceptible unless populations are extremely high.

How to Identify Citrus Leafminer Damage

The signs are unmistakable once you know them. New leaves show silvery, translucent, meandering trails that wind across the leaf like a little maze, usually with a thin dark line of frass (droppings) running down the center of the mine, and the leaves pucker, curl, and distort (UC IPM). Fresh, active mining looks silvery and translucent; once the larva has moved on, the old damage dries to a tan color. If you see a tightly rolled leaf edge, that is where the mature larva has curled the leaf around itself to pupate before emerging as a moth. For a closer look at the moth, the larva, and each stage from egg to adult, see our citrus leafminer identification and life cycle guide. You will see all of this only on new growth, which is the key to understanding how to handle it.

The Citrus Leafminer Life Cycle

The moth lays its eggs on new flush, the larva mines the leaf, and when it is done feeding it moves to the leaf margin, rolls the leaf around itself, and pupates, then emerges as an adult moth to start the cycle again. There are several generations a year. Damage builds through summer and fall, and in the mild coastal communities of Southern California, where citrus can flush for much of the year, leafminer can stay active nearly year round, while inland summer heat tends to suppress it (UC IPM). Coastal lemons, which flush repeatedly, tend to see the most activity.

Does Citrus Leafminer Harm the Tree?

For most backyard trees, far less than it looks. On a mature tree, roughly four years and older with a good canopy of older leaves, the damage is cosmetic and the tree tolerates it with negligible effect on growth and fruit yield (UC IPM). Young and newly planted trees are more vulnerable, because they have little mature foliage and push tender new flush all the time, so heavy mining can slow their growth. Even so, UC notes that even young trees with heavy leafminer populations are unlikely to die. In other words, this is a pest that looks alarming but rarely does real harm.

How to Get Rid of Citrus Leafminer

Here is the honest, research-backed answer that catches people off guard: on an established tree, the best thing to do is usually nothing. Leave the damaged leaves on the tree and let the natural enemies do the work, rather than reaching for an insecticide. The table below sums up the right approach for each situation.

Situation	What to do	Why
Established tree (about 4 years and older)	Tolerate it; leave the leaves on and let natural enemies work	Damage is cosmetic, with negligible effect on growth or fruit
Young or newly planted tree	Use cultural controls and protect the new flush	These trees flush constantly and can be slowed by heavy mining
Monitoring	Hang a pheromone or sticky trap	Catches the adult moths so you know when they are active
Avoid	Pruning off damaged leaves; broad-spectrum insecticides	The leaves still feed the tree, and broad sprays kill the natural enemies

Two “do nots” matter most. First, do not prune off the leafminer-damaged leaves, because the undamaged parts of those leaves keep producing food for the tree, and new flush will just get mined again anyway (UC IPM). Second, avoid broad-spectrum insecticides such as malathion, carbaryl, and pyrethroids: they struggle to reach the larvae protected inside the mines, and they kill the beneficial insects that keep leafminer and other pests in check, which can trigger flare-ups of whiteflies, scales, aphids, and mites (University of Georgia Extension). The most useful thing you can do on any tree is cultural: do not apply high-nitrogen fertilizer when leafminer is active in summer and fall, since it pushes exactly the tender flush the pest wants, and prune live branches no more than once a year, timed so the flush does not coincide with peak moth activity. The goal is to let each flush harden off quickly.

Protecting a Young Tree (If You Decide to Treat)

If a young, newly planted tree is getting hit hard and you feel you must intervene, target the new flush and keep it gentle. The materials extension programs recommend are spinosad (sold under brand names such as Captain Jack’s) and neem oil (azadirachtin) or a horticultural oil; UC notes these have some efficacy but short-lived residues, so they must be applied to new growth and reapplied about every 7 to 14 days while the flush is tender (UC IPM). Oils work by coating and smothering, so cover the new leaves thoroughly, do not spray in hot, sunny weather, which can injure the foliage, and stop once the leaves harden off (University of Georgia Extension). Spinosad has the advantage of being relatively easy on the natural enemies. As with any pesticide, read, understand, and follow the product label before you apply it, and when in doubt bring a leaf sample to one of our nurseries so we can confirm what you are dealing with first.

Encourage the Natural Enemies

The reason tolerance works so well is that citrus leafminer has help keeping it in check. In California, tiny native parasitic wasps (Cirrospilus and Pnigalio species) lay their eggs in the leafminer larvae inside the mines, and UC notes you do not need to buy or release parasites; they show up on their own (UC IPM). (In Florida, a different wasp, Ageniaspis citricola, was introduced for the same purpose and is now well established, per UF/IFAS.) You can support these beneficial insects by growing nectar plants they feed on, such as daisies, salvias, and lavenders, and by not spraying broad-spectrum insecticides that would wipe them out. Removing the vigorous water sprouts and suckers that pop up on the trunk and above the graft also removes prime egg-laying flush; our guide to removing suckers and water sprouts walks through how.

Frequently Asked Questions

What is citrus leafminer?

Citrus leafminer is the larva of a tiny moth (Phyllocnistis citrella) that tunnels just under the surface of new citrus leaves. The feeding leaves squiggly silvery trails and curls the leaves. The adult moth is harmless; it is the larval mining stage on fresh flush that you notice.

What are the squiggly lines or worms on my lemon and citrus leaves?

Those silvery, winding trails on the new leaves are citrus leafminer mines, made by the larva feeding just beneath the leaf surface, often with a thin dark line of frass down the middle. The “worm” you may glimpse inside is the larva. It only attacks tender new growth, not hardened older leaves.

Does citrus leafminer kill the tree?

Almost never. On established trees (about 4 years and older) the damage is cosmetic, with negligible effect on growth or fruit. Young, newly planted trees can be slowed by heavy infestations, but even they are unlikely to be killed by citrus leafminer.

How do you get rid of citrus leafminer?

On a mature tree, the best approach is to tolerate it and let natural enemies control it; do not prune off the damaged leaves and do not use broad-spectrum sprays. On young trees, limit high-nitrogen fertilizer during summer and fall, prune only once a year, and, only if needed, protect the new flush with spinosad or a horticultural or neem oil.

Should I prune off the damaged leaves?

No. The undamaged parts of those leaves keep making food for the tree, and any fresh growth you force out will simply get mined again. Pruning off the damage does more harm than good, so leave the leaves in place.

Does citrus leafminer affect the fruit?

On established trees, leafminer has a negligible effect on fruit yield. It damages only the leaves, not the fruit directly, and a mature tree carries plenty of healthy foliage to ripen its crop.

What spray works on citrus leafminer?

Because the larvae are protected inside the leaf, most sprays reach them poorly. If a young tree truly needs treatment, extension programs point to spinosad or a neem or horticultural oil applied to the new flush and repeated every 7 to 14 days, stopping once the leaves harden. Avoid broad-spectrum insecticides, which kill the natural enemies that control the pest.

Sources

• UC IPM, Citrus Leafminer (Pest Notes, Home and Landscape)
• UC IPM, Citrus Leafminer (Pest Management Guidelines)
• University of Georgia Extension, How to Control Citrus Leafminers
• UF/IFAS Featured Creatures, Citrus Leafminer

Citrus leafminer looks worse than it is, and most of the time your tree does not need you to do a thing. If you are not sure whether your tree is mature enough to shrug it off, or you want help choosing a gentle treatment for a young tree, stop by your favorite Green Thumb Nursery location with a leaf sample and we will walk you through it. While you are caring for your citrus, our guide to rootstocks for fruit trees is a helpful companion read.

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