Leek moth

What you see

Small caterpillars, pale with brown heads, tunnelling inside the leaves and shaft of alliums, leaving white windowed streaks.

Damage

White or translucent streaks running down the leaves, then rotting at the point of entry. Onions and leeks rot from the neck.

Lifecycle on this coast

Two or three generations, spring to autumn. Overwinters as an adult in sheltered debris.

When to act

Low tolerance on leeks - once tunnelling reaches the shaft the plant usually rots.

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

Plants it bothers

Leek, Onion, Garlic, Shallot, Chives, Spring onion, Welsh onion

Natural enemies

Parasitic wasp (Diadromus), Ground beetle

Remedies

Insect mesh and fleece barrier, Bacillus thuringiensis (Bt)

The thing people get wrong

Mesh over the leek bed from planting is the whole answer, because once the caterpillar is inside the leaf no spray reaches it. If you find windowed streaks, squeeze the leaf between finger and thumb along the tunnel - you kill the larva through the leaf without opening the plant.