This is a problem that can affect all plants in the citrus family. Every summer, flushes of new growth fall victim to attack from the ‘citrus leafminer’.
It starts with the adult, a tiny moth that flutters around at night laying eggs on the fresh new foliage. When they hatch, the little larvae or grubs burrow and ‘mine’ their way into the leaf creating their familiar silvery track marks. When the grubs have had their fill, they move on over to the edge of the leaf and curl it into a cosy shelter where they pupate.
While this activity makes the foliage look ugly and unhealthy, the trees usually survive the attack. It’s OK to prune it off, but not really necessary. The leaves will continue to photosynthesis and produce energy for the tree. However, they would function much better if they weren’t damaged and distorted in this way.
The pest can be controlled organically using an oil-based spray. It’s not used to smother the larvae; instead, it’s applied on the new leaves as soon as they appear, making conditions unfavourable for the adult moth - they won’t lay their eggs on an oily surface. The moth is most active during the summer months so you need to be ready to spray then. Avoid spraying during the heat of the day – that can burn the leaves - wait until the cool of the afternoon. And keep an eye on things - you may need to follow up with a fortnightly spray to maintain a coating of oil on the leaves.
Homemade oil spray
It’s easy to make a low cost oil spray at home. Pour 2 cups of vegetable oil and ½ cup of dishwashing liquid into a jar, mix it well then add 1 tbsp of concentrate to 1 litre of water. Spray to cover the top and bottom of the foliage.
First published: April 2010