Imidacloprid Fate and Transport In Florida Flatwoods Soils During Control Of Asian Citrus Psyllid.

Imidacloprid (IMD) is a systemic pesticide soil-drenched to control the citrus greening primary vector Diaphorina citri Kuwayama, or Asian Citrus Psyllid (ACP). Fate and transport studies were conducted after IMD applications in Florida Flatwoods soils of the Immokalee Fine Sand series.  IMD sorption and degradation studies showed a weakly-sorbed (K_OC 200) and persistent pesticide (t_1/2 1.3-2.3 y) with high leaching potential. Field experiments were established in nonbearing citrus trees (Hamlin Orange US 802) during four seasons: summer 2011, spring 2012, summer 2012, and spring 2013. IMD and Br^- tracer were soil-drenched in a 41 cm diameter circle around the tree stem base (PA). The treatments were applied in a non-planted area (NPA) with no root zone effects. Soil sampling was done with bucket augers in 15 cm increments to a 75 cm depth. The sampling dates were scheduled two times per week the first 2 weeks, and weekly until the season was over (4 & 6 weeks for summer and spring, respectively). The tracer leached out in less than 1 week after application. IMD leached out from the root zone about 4 weeks after application in summer, and from 6 to 8 weeks in spring. IMD (μg g soil^-1) showed higher concentrations for NPA than the PA as a function of time. The difference was due to the plant root uptake. However, there was an effective systemic control on the ACP on soil-drenched trees, especially after week 2. This trend continued 8 weeks after application where treated trees showed lower ACP adult counts and lower immatures ACP infestation rates (eggs and nymphs presence) in young leaves flush. Finally, we have developed an extraction protocol for IMD in citrus leaves using HPLC-MS/MS detection. Tissue data are in close agreement with our findings in soils and on ACP systemic control.