Leaf miners

Leaf miners are the larvae of various insects, including flies and moths, that live and feed inside leaf tissue, between the two epidermal layers. The adult female lays eggs in the leaf, and the newly hatched larva tunnels through the parenchyma, the internal tissue responsible for photosynthesis. An uncontrolled infestation reduces the plant's ability to produce energy, causing general weakening and potentially premature loss of the most affected leaves.

Signs to check

• Winding, whitish-yellow trails visible through the leaf tissue.
• Trails that do not rub off because they are inside the leaf.
• A possible small dark point, the larva, at the widest end of the tunnel.
• Tunnels that gradually widen as the larva grows.

What you may notice

• Leaf miner tunnels · Whitish or yellowish winding tunnels run inside leaf tissue, between the two epidermal layers.

What to do now

Stop leaf miner tunnels

1. Carefully inspect every leaf on the plant. Locate each tunnel.
2. Immediately cut off and discard all heavily affected leaves. Do not compost them, to avoid spreading the infestation.
3. For leaves with only one or two tunnels, crush the larva inside with your fingers. Follow the tunnel to its end, where you will feel a small hard point: that is the larva.
4. Place yellow sticky traps above the plant. They catch adult flies and help you monitor the infestation.
5. Spray a solution made with neem oil. Mix 5 mL (about 1 US tsp) of neem oil and 1/2 spoonful of black soap into 1 liter (about 1.06 US qt) of lukewarm water. Apply to both sides of leaves every 7 days.

Prevention

• Inspect leaf undersides once a week for early egg-laying punctures.
• Quarantine every new plant for 2 to 3 weeks before placing it near others.
• Keep yellow sticky traps in place as an early warning system.