If you’ve attempted to grow citrus of any variety in your backyard, the chances are that you are familiar with Phyllocnistis citrella – the citrus leafminer.
Amazingly, this prolific pest was only identified in 1993 in Florida. Since then, it has spread far and wide and sadly, it is well-known here in Australia. Even worse, it isn’t fussy about the kind of citrus on offer either with everything up to and including native finger limes under possible threat
What is Citrus Leafminer?
Sometimes called the citrus leaf miner, it is actually a small, nocturnal moth with a wingspan of only 5mm.
The pregnant females lay their eggs on new growths of citrus leaves. When the eggs hatch, the tiny larvae that emerge promptly tunnel – like miners – into the leaf where they feed. As they move around under the skin of the leaf, they eat out tracks – or mines – which pattern the leaves with silvery thread-like scars.
Infestation by citrus leafminer grubs can result in the leaves of the plant becoming deformed and curling up. Indeed, the larvae pupate in a cocoon made by bending the edge of a leaf over and fixing in it place with silk. In warmer months, the life cycle of the citrus leafminer can be over within just a fortnight and it’s possible for the pest to produce up to 15 generations in a single year. So once you find them in on oranges or lemons, you want to act fast and get rid of them.
Whilst older citrus trees can generally survive an attack, partly because their leaves are tougher for the larvae to bury into and so less appealing, partly because they aren’t as reliant on new leaf flush. However, the growth of younger plants can be badly affected – particularly as the insect loves fresh, succulent leaves.
How to Treat Citrus Leafminer
The first thing is to spot the signs of citrus leafminer before it takes over:
- Monitor the new growth on your citrus plants – check for twisted or deformed leaves.
- Check for the tell-tale silvery mines – especially on the underside of newly sprouted leaves.
If you find evidence of larva activity, act fast. There are a number of non-chemical options if you want to try to eradicate the problem without resorting to pesticides:
- Remove the infected leaves – take off any scarred leaves and dispose of them. This isn’t too hard to do if you only have a couple of kumquats in tubs to keep an eye on, but it becomes more challenging if you have a citrus orchard to watch over.
- Balance removing infected leaves with feeding and watering your citrus plant to help it outgrow the phase where it is susceptible to the damage done by the larvae.
- Spray with White Oil (a horticultural oil) – useful to fight all kinds of infestations, this homemade citrus leafminer deterrent is cheap, easy to make, safe and – best of all – effective. Simply pour 2 cups of sunflower or vegetable oil to a large jar or bottle with a screw top. Add 1/2 cup of regular household dishing liquid. Screw in the lid and shake. The mixture will turn an opaque, milky colour – hence the name White Oil. When you want to use it, decant 2 tablespoons of the concentrate into a bottle with a spray attachment. Add 1 litre of water and mix. Spray it onto both sides of the leaves.
- White Oil works on citrus leaf miner by deterring the moths from laying their eggs. It is best applied when your citrus trees are flushing with new growth and needs to be done regularly (every few days) to ensure that the moths don’t find a window to lay their eggs. If the eggs get laid, the larvae will hatch and bury into the leaves where the White Oil has no reach.
- With other species of pest, scales and moulds etc, White Oil works by suffocating them.
- Take a look at this clip for more on the uses of White Oil.
- Make sure to only use White Oil in cooler days. If the temperature gets above 30C, it may cause burn damage to your plants.
- Use citrus leaf miner lure traps – male and female citrus leafminers use sex pheromones to communicate when mating. Disrupt the pheronomes and communication break down, which means that the male and female adult moths fail to get together and reproduce. There are a number of citrus leafminer traps on the market and they offer an environmentally friendly method of controlling leafminers, whilst other species of insect at left in unaffected.
- Net your citrus tree – you can cover the citrus plants in protective mesh netting to keep both insects and birds at bay.
- Neem Oil – made from the seeds of the neem tree, it is an effective natural pesticide. Neem Oil is absorbed by the targeted citrus plant through its soil and is spread around the citrus and ingested by the larvae of the citrus leaf miner when they are feeding on the leaves. The result is that they stop tunnelling into the foliage and fail to mature.
Of course, if you aren’t on the hunt for a natural way to control citrus leafminer infestation, there are a number of chemical options on the market:
- Amgrow 81015 Insect, Fungus and Mite Control Spray – contains both a fungicide and insecticide to protect your citrus crop against a range of nasties.
- Brands such as Yates and Bayer also offer products.