# Leafminer

> Insect larvae, on cannabis mainly Liriomyza fly maggots (family Agromyzidae), that tunnel between the leaf surfaces, leaving pale winding trails.

- Canonical: https://genetixbay.com/knowledge/glossary/leafminer.html
- Also written: leafminers, leaf miner, leaf miners, Liriomyza, agromyzid fly
- Glossary category: Pests and diseases · Evidence: Supported
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A leafminer is any insect larva that feeds inside a leaf, between the upper and lower surfaces. On cannabis the usual culprits are small agromyzid flies, mainly *Liriomyza* species. The adult female punctures the leaf to lay eggs; the larva then eats a pale, winding tunnel that widens as it grows, and finally drops out to pupate in the medium.

## In practice

Leafminer trails are distinctive: serpentine white or tan lines, often with a dark thread of [frass](https://genetixbay.com/knowledge/glossary/frass.md) down the middle. Damage on cannabis is usually cosmetic and limited to [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), mostly outdoors or in greenhouses. Picking off mined leaves and destroying them breaks the cycle. [Yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) catch adults. In greenhouse crops, [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) such as *Diglyphus isaea* are used against them. Because larvae are protected inside the leaf, contact sprays do little. Check what is registered for cannabis locally.

## Don't confuse with

- **Thrips**: surface scraping with silvery patches, not tunnels.
- **Spider mite stippling**: tiny dots, no trails.
- **Septoria leaf spot**: round spots with dark margins, not winding lines.

## Related terms

[Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md)

## Sources

1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects