Tomato leafminer

What you see

You almost never see the moth (5-7 mm, silvery-brown, night-flying). What you see is its work: irregular blotchy mines inside the leaf with black grains of frass visible through the leaf surface, and pinhole entry wounds in green fruit.

Damage

Blotch mines that look like brown paper windows in the leaf. Small round holes in fruit near the stalk, with a rotting tunnel and frass inside. Whole plants can be skeletonised in a bad year.

Lifecycle on this coast

Up to 10-12 generations a year in a Mediterranean climate. Overwinters as pupa in soil or plant debris and in volunteer tomato plants - which is why last season's tidy-up matters more than any spray.

When to act

Zero tolerance on fruit. Hang pheromone traps in April; the first catch tells you to begin protecting. Any mined leaf should be removed and binned, not composted.

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

Plants it bothers

Tomato, Aubergine, Potato, Pepino melon, Tomatillo

Natural enemies

Minute pirate bug, Trichogramma parasitic wasp, Lacewing

Remedies

Pheromone traps, Bacillus thuringiensis (Bt), Insect mesh and fleece barrier, Encourage predators

The thing people get wrong

This is the single most destructive tomato pest in Portugal and the fight is won in winter, not summer. Pull every tomato plant and every self-sown seedling at the end of the season, bin the debris rather than composting it, and rotate the bed. A garden that leaves old tomato stems standing is breeding next year's infestation on purpose.