Lepidoptera : Gracillariidae
Citrus Leafminer is an introduced pest from South-East Asia that can occur on all varieties of citrus and is found in all areas of Australia where citrus trees are grown. They are called ‘leafminers’ because the larvae tunnel or ‘mine’ under the surface of citrus leaves. Citrus Leafminer is the only leafminer that occurs on citrus in Australia.
Typical damage caused by Citrus Leafminer larvae is silvery trails or ‘mines’ on citrus leaves and distorted citrus leaves. Severe infestations can negatively affect the growth of young trees, but the damage is mostly insignificant to mature (i.e., older than about 5 years) trees.
The best way to prevent and control a pest like Citrus Leafminer is to understand its life cycle and where and how the larvae feed – they are inside the leaves of a citrus tree. You can learn more about Citrus Leafminer life cycle in the section below. In the garden, the best thing to do is to keep any eye on your plants and watch for any flush growth emerging. This is when your plants are most vulnerable to attack.
There are several measures that you can take to prevent or minimise damage by Citrus Leafminer (see How to Prevent Citrus Leafminers Appearing). Apply Yates PestOil Concentrate as soon as you see flush growth. This prevents the moth laying eggs and, if you time it correctly, you may avoid Citrus Leafminer damage entirely. If the pest is common in your area you may need to reapply oil periodically, once a week or so, until the flush growth hardens off.
If the moths get through your defences and leaf mines appear on your citrus leaves, try Yates Success Ultra. This pesticide has ‘translaminar’ action, meaning that the active ingredient (Spinetoram) is absorbed into the leaf and is effective against Citrus Leafminer larvae inside the leaf. Always follow label instructions.
Citrus Leafminers are the larvae (caterpillars) of tiny moths of the family Gracillariidae. There are about 500 species of this family that occur in Australia, but this is the only species that attacks citrus.
The adult Citrus Leafminer is a tiny nocturnal moth with a 4 mm wingspan. You are unlikely to see them in your garden, due to their diminutive size and nocturnal habits. The moths are whitish in colour with some brown markings and they have fringed wings.
Citrus Leafminer larvae are translucent greenish-yellow, about 3 mm long, and somewhat arrow-shaped. Larvae are well hidden in their characteristic, sinuous ‘mines’ inside citrus leaves.
Citrus Leafminer pupae are about 2.5 mm long, pale brown coloured, and usually located in a rolled over leaf edge.
Moths lay single eggs on the underside of young leaves, usually at the base of the leaf. The eggs hatch in 2-10 days depending on the temperature, and the tiny larvae burrow under the leaf surface.
Larvae pass through three larval stages (instars) and a non-feeding pre-pupal stage. Larval development time can be anywhere from about 5 days to 3 weeks depending on the temperature.
Larvae pupate inside leaves by bending over the leaf margin and holding it together with silk. Pupation takes from 6 days to 3 weeks, depending on the temperature, before an adult moth emerges.
The life cycle can be completed in about two weeks during warm weather and there may be as many as 15 generations per year. Overwintering usually takes place in the larval or pupal stage.
Image above: symptoms of citrus leaf miner damage including
silvery trails, twisted and curled leaves of citrus.
(image courtesy of Elise Dando)
The flush growth of all varieties of cultivated citrus. Mature leaves that have hardened off are not susceptible. Young trees are vulnerable because they tend to produce more flush growth, and don’t have much mature foliage. Severe infestation may result in retarded growth of young trees, but their effect on mature trees is much less serious and often only unsightly. Adult Citrus Leafminer moths are harmless – any damage to citrus is caused by the larvae.
Twisted and curled leaves of new growth are the most obvious symptoms, along with trails or ‘mines’ in the curled leaves. The serpentine mines have a silvery appearance and reach a length of 50 mm to 100 mm.
Image above: underside of citrus leaf with old damage of trails
(image courtesy of Elise Dando)