Citrus greening disease (Huanglongbing, HLB) has damaged the citrus industry worldwide. With over 90% of Florida’s oranges infected, growers are desperate to improve management strategies and slow the spread of this detrimental disease. Insecticide application efficacy in the field was investigated with liquid chromatography tandem mass spectrometry to determine if insecticide applications to citrus were effective at killing the responsible pest, Asian citrus psyllids (ACP). Sample discs attached to leaves were sprayed with imidacloprid, malathion, dimethoate, and afidopyropen at a field site in Florida. Application method, canopy height and depth, cardinal side of tree, and leaf side were considered to assess spatial distribution of insecticides throughout citrus trees. Leaf samples were collected at various times after insecticide application to assess degradation. ACP were inspected in trees before and after insecticide applications to quantify psyllid reductions and application efficacy. Our findings show that while concentrations were high enough to kill ACP, the spatial distribution of insecticides throughout individual trees was highly variable and live ACP were detected after application. Inadequate distribution to different areas of the tree canopy, including top side of leaves receiving significantly more insecticide than undersides, was observed for all application methods tested. Preliminary results show insecticides degrading below the LOD within 3 days after application. Inspections of ACP populations before-and after-insecticide applications resulted in efficacies of 85-100% (malathion), 48-80% (imidacloprid), 60-84% (dimethoate), and 33-77% (afidopyropen) with a majority resulting in population increases (ranging 145-600%) when inspected 9 days after application. The variability in insecticide spatial distribution due to application method and rapid degradation of insecticide active ingredients allows remaining ACP to continue spreading citrus greening disease to unprotected trees. Further research is needed to improve insecticide application methods for citrus trees and implement effective pest management strategies and fully target ACP to eliminate HLB.

Quantifying insecticide application efficacy and degradation within a citrus greening disease infected grove

ACS Spring Meeting 2021

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