Citrus leafminer
Description
Adult CL are small (2 mm) and silvery white moths with narrow wings that are fringed with long hairs. Females tend to be more prevalent than males. Eggs are laid singly in the evening, near newly emerged leaves and one female can lay up to 50 eggs. Eggs are very small (0.3 mm), flattened and slightly oval, they are translucent but appear light green from the leaf below. Within 2 -10 days eggs hatch and larvae emerge, initially they are pale green and hard to see. As CL larvae feed they excrete their faeces into their mine, creating a visible trail. CL larvae are unable to move from leaf to leaf, consequently they remain on the same leaf until they pupate. Pupation in CL begins when larvae mine near the leaf margin, causing it to fold over and silk produced by larvae forms the remainder of the chamber. Pupae are yellowish brown in colour and 2.5 mm long. Within six days adults emerge through an opening in the chamber.
Young leaves and foliage are most commonly attacked by CL larvae. Feeding larvae produce a snake-like mine or tunnel in the leaves, causing leaf twisting and curling. Fruit and stems can be attacked, although this seldom occurs. In older trees (>5 years) damage can appear unsightly, however yield losses, as seen in younger trees, are not common.
Control
Natural predators play an important role in control of CL, including; lacewings and three parasitic wasps, Ageniaspis citricola and Cirrospilus quadristriatus (both introduced) and Semiolacher petiolatus which is native to Australia. Preserving these populations by minimising broad spectrum insecticide use is important.Apply fertiliser during winter so flushes of fresh growth, which is favourable to CL, occurs in spring when CL populations are low. Avoid overwatering during summer and autumn to reduce the amount of new growth, which lowers the chance of creating an ideal environment to support an outbreak of CL.
Control of CL with insecticides can be difficult as larvae remain concealed within the mines. Most sprays are broad-spectrum and disrupt natural predator populations. Soap or pest oils are a good alternative to insecticides, care should be taken when applying oils in warm (> 35 °C) conditions. If a severe infestation occurs, particularly in younger trees, an insecticide may be required.
Confidor® Guard is a systemic insecticide registered for the control of CL in citrus, and should be applied in late spring after flowering has finished.
References
Broughton, S (2018), ‘Citrus leafminer’, Department of Primary Industries and Regional Development, https://www.agric.wa.gov.au/citrus/citrus-leafminerPestNet (Viewed Dec 2019), ‘Citrus leafminer’, Pacific Pest and Pathogens Fact Sheets, http://www.pestnet.org/fact_sheets/citrus_leafminer_240.htm
Hardy, S (2004), ‘Citrus leafminer’, NSW Department of Primary Industries (DPI), Agfact, fourth edition, https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/137634/citrus-leafminer.pdf