Citrus leafminer

This tricky pest feeds on citrus leaves, causing unsightly foliage distortion

It’s common to see damage caused by citrus leafminer on citrus trees in summer and autumn. The tell-tale sign is distorted new foliage covered in wiggly silvery lines. The adult citrus leafminer is a tiny moth, which you rarely see because it’s only active at night. The female lands on young leaves and lays its eggs along the midrib. When the larvae hatch, they tunnel just under the leaf surface, feeding on the sap. This tunnelling causes the distinctive silvery lines. When a larva has had its fill, it heads for the edge of the leaf and curls it over to create a shelter, where it pupates then re-emerges as a fully fledged adult moth, and the cycle starts again. The entire process happens in 2–3 weeks, so it doesn’t take long for a significant amount of damage to accumulate.

So, what should you do about it? Generally, if the tree is well established, it copes with the attack and will still flower and fruit as normal. It looks a little ugly for a while, but you don’t have to do anything. However, if you can’t stand the sight of the damage, you can prune off and dispose of the worst-affected leaves. Just be careful not to remove any flowers or fruit, or prune the tree too hard, which will remove fruiting wood. Citrus leafminer is only active in summer and early autumn, so the spring foliage flush won’t be affected by this pest.

Young trees can be set back by a heavy attack, and if this happens, it’s best to take measures to control the pest. One simple approach is to visit the tree every few days through the summer/autumn period to inspect the leaves. If you see any fresh tunnels, squeeze them between your thumb and forefinger to squash the larvae.

Another control that can be used for small and mature trees is to spray new foliage with a horticultural oil spray. Adult moths tend to avoid leaves with an oily surface, so there will be far fewer eggs laid. Reapply every 10 days or so to ensure minimal foliage damage.