Plant Doctor Archive

Patchy leaves on echium

MY Echium 'Cobalt Tower' has something wrong with its leaves. Most seem to be dying off and others have funny tines on them. Can you help?

THE sample you sent contained leaf miner caterpillars, the larvae of small moths which lay their eggs on the leaves. On hatching, the young caterpillars burrow into the leaf and create tunnels between the upper and lower surface. At first you'll see long, relatively clear, tunnels, but as damage gets worse these can merge into large dead areas, as has happened to your echium.

Hold a badly affected leaf up to the light and you should be able to spot the small caterpillars wriggling around inside, nicely protected inside their tunnels. I split one of the leaves open to reveal the caterpillars you see here.

Protected inside their tunnels, leaf miners can be difficult to control. In the early stages of attack you could remove damaged leaves but as your echium has most of its leaves infested you'll need to spray with a systemic insecticide such as Target or Rogor, which travels through the plant cells to be ingested by the leaf miners as they feed. Follow the label recommendations carefully, especially with regard to protecting yourself when mixing and applying these sprays.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.