Intro

Citrus leafminer, Phyllocnistis citrella are the only mining insect that commonly attacks citrus leaves. Leafminer larvae feed by creating shallow tunnels, or mines, in young leaves of citrus trees. Citrus leafminer are very small, light-colored moths, less than 1/4 inch long. It has silvery and white iridescent forewings with brown and white markings, and a distinct black spot on each wing tip. The hind wings and body are white, with long fringe scales extending from the hind wing margins. The larval stage can only be found inside self-made mines of citrus leaves and other closely related plants.

Origin

The citrus leafminer is native to Asia. They were first detected in California in 2000, in Imperial County. It soon spread to adjacent counties and continued to move northward. Citrus leafminer now infests most of southern California, from the coast to as far north as San Luis Obispo County, and the San Joaquin Valley.

Hosts

The pest is most commonly found on citrus (oranges, mandarins, lemons, limes, grapefruit, and other varieties) and closely related plants (kumquat and calamondin).

Damage

The flush growth of citrus trees attacked by leafminer will look unsightly. Citrus leafminer can survive as a larva only in the tender, young, shiny leaf growth of citrus and closely related species. As it feeds and develops, the larva leaves a dark thin line of frass (feces) inside the meandering serpentine mine. Older leaves that have hardened off are not susceptible to attack unless extremely high populations are present on the host.

The larvae mine inside the lower or upper surface of newly emerging leaves, causing them to curl and look distorted. Mature trees with a dense canopy of older foliage to sustain them can tolerate damage on new leaves during part of the growing season with negligible effect on tree growth and fruit yield. Young trees may experience a reduction in vigor or stunting. However, even young trees with heavy leafminer populations are unlikely to die. Hot summer temperatures in the inland areas of California suppress leafminer populations, but in temperate coastal areas, the insect population may remain high from summer through fall.

Life cycle

The entire life cycle of the insect takes 3 to 7 weeks to complete. Citrus leafminers develop best at temperatures between 70º to 85ºF and greater than 60% relative humidity, but they will readily adapt to most of California. They will hatch and grow in the leaf, curl the leaf to pupate, and then they emerge as adults that will continue the generations.

The natural enemies of the citrus leafminer feed on and parasitize the larvae in the mines, using insecticides kill these beneficial insects and can worsen the pest problem.  Letting the predators control their numbers benefits not only your tree but your neighbors trees as well.

Quarantine/Recommendations

Do not apply fertilizers high in N (nitrogen) during the peak seasons for this pest. New growth will help feed subsequent generations, and it will lead to sever infestations.

 

 

 

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