Leaf miner

What you see

Never the insect - just its handwriting: pale winding tunnels traced through the inside of a leaf, widening as they go.

Damage

White or translucent squiggly tunnels in leaves. Heavy mining reduces vigour but rarely kills.

Lifecycle on this coast

Several generations. The tiny fly lays eggs into the leaf; the larva mines between the leaf surfaces then usually drops to pupate in the soil.

When to act

Largely cosmetic - tolerate freely on ornamentals and mature plants. Act only on seedlings, or on leaf crops where you eat the leaf.

Months: April, May, June, July, August, September

Plants it bothers

Celery, Celeriac, Beetroot, Swiss chard, Tomato, Lettuce, Spinach

Natural enemies

Parasitic wasp (Diglyphus), Minute pirate bug

Remedies

Yellow sticky traps, Encourage predators, Neem oil spray

The thing people get wrong

Squash the mine, not the plant: run your fingernail along the end of the tunnel and you crush the larva inside without removing the leaf. Spraying is nearly useless anyway - the insect is sandwiched safely between two leaf surfaces where nothing wet can reach it.