How to control leafminers to prevent damage to crops
Leaf miners damaging plants (Illustration: Ecologiaverde.com)
Characteristics of leafminers
The adult citrus leafminer is a small moth, 2-3 mm in body length with a wingspan of 4-5 mm. The entire body is pale yellow with a silvery sheen. The hindwings are very narrow compared to the forewings, and both pairs have long fringe hairs along the margins.
Eggs are oval-shaped, small, measuring 0.2–0.3 mm. Initially transparent, they turn yellowish-white when close to hatching.
Fully grown larvae are 4 mm long, flattened, legless, with a long tube-like final abdominal segment.
The pupa is about 2–3 mm long, yellowish-brown, with a tubercle on the lateral side of each body segment, bearing a hair on top.
Moths are active at night, usually laying eggs on the undersides of leaves near the main veins of newly sprouted young shoots. An adult citrus leafminer typically lays 70-80 eggs, with an oviposition period lasting from 2 to 10 days.
Newly hatched larvae typically bore through the epidermis of the leaf to feed on the leaf parenchyma, creating winding tunnels beneath the epidermal layer, followed by a thread-like trail of frass; the epidermis may peel off or look like snail slime. The leaf miner tunnels become longer and larger as the larva grows.
When fully mature, larvae bore out to the leaf edge and pupate near leaf veins where the leaf is curled, using silk to fold the leaf and shield their cocoons.
How leaf miners damage crops
When pests cause damage, leaves become small and deformed, affecting the development of young shoots. Flowers and fruits may drop when infestation is severe. During the seedling stage, frequent damage leads to poor growth and smaller-than-normal canopies. Citrus leafminers are also vectors transmitting citrus canker.
Leaf miners cause damage year-round, but attacks are concentrated and severe in July, August, and September, as plants produce abundant young shoots during this period, providing plenty of food. Favorable conditions for the pest's damage are typically temperatures between 23 and 29°C and humidity levels between 85 and 90%.
Leaf miners usually damage young shoots and tender leaves. As soon as young leaves emerge, newly hatched larvae bore through the leaf epidermis to feed on the soft internal tissues; wherever they feed, the leaf epidermis blisters, forming serpentine tunnels.
How to prevent leafminer infestations
Regularly monitor and inspect orchards to protect flushes of young shoots, detecting pests promptly to take appropriate action.
In cases of severe pest infestation, prune and remove damaged branches, leaves, and young shoots, and destroy them properly.
Preventive spraying should be conducted before each new flush of young shoots using appropriate biological pesticides.
Care for the trees to ensure healthy growth, prune branches, shape the canopy, and apply top-dressing fertilizers so that young shoots emerge uniformly, limiting pest damage.
Provide crops with balanced nutrition using organic fertilizers, foliar fertilizers, and secondary and micronutrients to enhance plant resistance. Well-nourished crops grow vigorously with large leaves and thick cuticles, making it difficult for young larvae to penetrate the foliage and thereby reducing pest damage.
In addition, it is necessary to protect and foster natural enemies in the garden, such as weaver ants and parasitic wasps, to naturally eliminate leafminers.