Impact of Insecticide Treatments for Phyllocnistis citrella (Lepidoptera: Gracillariidae) on Growth and Yield of Young Citrus reticulata Mandarins.

The citrus leafminer, Phyllocnistis citrella Stainton, is an invasive pest of citrus whose larvae damage developing leaves, which can impact tree photosynthetic capacity and may ultimately reduce tree growth and yield. Damage is most pronounced in young trees due to their greater propensity for production of new foliage, which supports P. citrella oviposition and larval development. We studied P. citrella damage and tree growth and yield among different insecticide treatment regimes to gauge their effectiveness at protecting young citrus trees. Three levels of insecticide treatments were applied over 3 yr to 'Tango' mandarin (Citrus reticulata Blanco) citrus trees planted in the prior summer, which were inspected regularly along with untreated trees. Leaves suitable for oviposition by P. citrella were available during all census dates, though their numbers fluctuated in the summer months. Phyllocnistis citrella were suppressed for 2-3 wk by systemic or foliar treatments of insecticides. The higher number of treatments provided more sustained suppression of larvae. Trunk diameter was unchanged and canopy volume affected by only the most aggressive treatment regime. However, citrus yield was 2-2.5 times higher following the second year of treatments and 1.2- to 1.8-fold times following the third year of treatments for trees in the treatment regimes that included systemic imidacloprid plus 2-3 or 4-5 foliar applications, respectively, relative to untreated controls. Suitable leaf flush and larval densities declined over the 3 yr of the study. These data support the use of insecticidal control of P. citrella to protect young 'Tango' mandarin trees, but demonstrated that frequent applications are necessary to suppress populations.