Leafminer is a potentially serious pest of citrus and related Rutaceae and some related ornamental plants. Researchers first documented the citrus leafminer Phyllocnistis citrella, in Dade County, Florida, in 1993. Leafminer damage to foliage can stunt the growth of young trees and make trees more susceptible to citrus canker where the pathogen is present. Mature trees can better tolerate the damage although heavy infestations may reduce production. Adult citrus leafminers are small, silvery moths with a wingspan of 4 millimeters.
The wings have several black and tan spots with a small black dot on the wingtips. The adults are seldom seen and are active in the mornings and evenings. Female moths lay eggs on the underside of new foliage.
When the egg hatches, the larvae enter the leaf and meander through the leaf causing damage and malformed foliage. The larvae then pupate before the adult moth emerges. The adults only live a few days. The life cycle can take from 13 to 52 days depending on conditions. In Florida the life cycle is about 21 days, and populations peak in summer and early fall.
Biological control: In Florida, biological control and applications of oil are suitable methods to help reduce populations of CLM. Natural enemies already present in Florida have responded to leafminer infestations, causing up to 90% mortality of larvae and pupae. These natural enemies include the introduced parasitoid Ageniaspis citricola that is established throughout most of Florida and is responsible for up to 30% of this mortality mostly later in the year. For more on management, visit the Florida Citrus Pest Management Guide.
Chemical control: Leafminers are effectively controlled in young trees by systemic insecticides applied against ACP. Soil applications of neonicotinoids should be made about 2 weeks prior to leaf expansion to allow time for the pesticide to move from the roots to the canopy. Applications of neonicotinoids in summer should be timed to avoid rain events within 24 h, which would cause leaching of product away from the root zone. The appearance of leafminers in young flush of these trees is an indication that residual effects have worn off and reappearance of ACP is soon to follow. Foliar applications of products effective against CLM target larvae and at best provide no more than 3 weeks protection. Therefore, optimal timing is important, and sprays directed against CLM should be applied when flush is about halfway extended to kill the maximum number of larvae. For recommended chemicals to control citrus leafminer please refer to EDIS document.