By Lukasz Stelinski
The citrus leafminer (CLM) remains a major pest of citrus throughout Florida. The adults are small, white/silver colored moths about half the size of a typical mosquito (Figure 1). Adults are difficult to spot because of their small size and because they are active only in the evening (dusk) and early pre-dawn hours.
CLM adults can be monitored with sticky traps baited with commercially available pheromone lures. Only male moths are captured because the lures contain the female-produced sex-attractant.
After mating, females deposit eggs on young leaves, the most susceptible stage for infestation. The emerging larvae burrow into the leaves and feed within galleries just beneath the leaf surface. This is the stage of the leafminer that is typically most visible, and this is the stage when the damage is already taking place or has already been done.
Insecticides that kill larvae are currently the most accessible tools for CLM control. The early larval stage is the most susceptible and best target to avoid injury as larvae emerge from the egg and begin to feed on flush. Young trees are often the most susceptible to CLM damage because they produce young flush frequently.
Proper timing of foliar sprays to coincide with flushing cycles is critical to optimize CLM management. The goal is to kill larvae as soon as they begin mining. Although broad-spectrum insecticides targeting Asian citrus psyllid (ACP) adults may kill adult CLM, typically populations rebound in groves soon after foliar sprays of organophosphate or pyrethroid insecticides. Populations may even increase under intense ACP management due to suppression of natural enemies.
Applications of foliar insecticides should be made during a window when CLM larvae hatch and begin feeding to maximize larval kill. In general, the earliest applications should occur between 13 and 30 days after budbreak. The duration of control may be shorter if a heavy flush occurs soon after the foliar application. It may be advantageous to target spring flush, even though CLM damage is not evident, to prevent buildup of populations that will cause damage later in the year.
Populations of CLM typically increase significantly on the initial spring flush (Figure 2) with a second major peak occurring again in late September/early October.
In addition to foliar sprays, soil applications of neonicotinoid insecticides (e.g., Admire Pro, Platinum 75SG or Belay 2.13 SC) can provide multiweek control of CLM in non-bearing trees and should be applied up to two weeks prior to a leaf flush in order to allow lethal concentrations of insecticide to accumulate in the foliage and also to control ACP. Insecticides recommended for leafminer control can be found here.
Lukasz Stelinski is a professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.