Question PATCHY PELARGONIUM

A friend grew some pelargonium cuttings and gave me a plant, but now the leaves are spotty and some have holes in them. It doesn’t look like normal slug damage. Any ideas?

W Hagan, Auckland Answer

Those blotchy, almost transparent patches look like damage caused by leafminers, the larvae of a range of flies and moths. Look closely – you should be able to spot the tiny blackish slug-like larvae in some of the spots, sheltering between the upper and lower layer of the leaf and feeding on the juicy, nutritious plant cells. Some leafminers create narrow winding tunnels in leaves, while others make these roundish patches. The adult female lays eggs on the leaf and the larvae eats its way in and feeds there, protected from the vagaries of weather and threats of predation by other insects and birds.

A wide range of plants can be affected by leafminers. Some are specific to the host plant, like the kākābeak leafminer, which is the larva of the fly Liriomyza clianthi, while others lay their eggs on a range of plants.

In the home garden, there’s seldom enough damage caused by leafminers to warrant control, though systemic insecticides will do the job if needed. If you spot them early enough you can simply squash them where they are, inside the leaf. Most plants recover quickly once the larvae have completed that stage of their life cycle and moved on, and I’m sure your pelargonium will do the same.