What is causing lines on my Citrus leaves?
Citrus leaf miner (Phyllocnistis citrella) is a pest whose larvae burrow under the leaf surface. This causes the new growth to distort and have characteristic ‘squiggles’ all over the leaf surface. A very low toxicity control method involves spraying weekly at the beginning of spring or when there are flushes of new growth in summer and autumn with horticultural mineral oils- some of the available products are Pest Oil or Bug Oil. It is important to spray regularly as soon as the problem appears as the oil is designed to smother the pests as they arrive and infest the plant. This treatment will also control scale insects on citrus and other plants such as gardenias, and can also help with other annoying pests such as mites and some species of thrip
Natural predators of the citrus leaf miner include small parasitic wasps and lacewings. The use of mineral oil sprays rather than insecticides will help keep populations of predators around to help in the control of leaf miners.
There are two cautions when using oil sprays- they should not be used on very hot days (above 32o C), and should not be used when plants are water stressed.