Why spray if you don’t need to? Putting the IPM back into cItrus IPM by ground truthing spray thresholds

Why spray if you don't need to? Putting the IPM back into cItrus IPM by ground truthing spray thresholds

Report Date: 06/08/2020
Project: 19-002   Year: 2020
Category: ACP Vector
Author: Lukasz Stelinski
Sponsor: Citrus Research and Development Foundation

Objective: Develop threshold-based models for current use in Florida citrus. The objective of this experiment is to optimize management of Asian citrus psyllid (ACP) by implementing an economic threshold for need-based timing of insecticide applications.  We investigated the relationship between insecticide rotation using various modes of action and implementation of specific pest threshold levels for timing of these insecticide applications. Our goal is to determine how these factors influence ACP and insecticide resistance management, as well as their economic viability. First, we monitored adult psyllid populations before and after application for three threshold levels by tap sampling (0.2, 0.5, and 1 adult per tap sample). There are two rotation schemes in replicated plots in an experimental grove in Lake Alfred. The effectiveness was evaluated by weekly counts of ACP adults. Tap samples were taken from 20 trees per replicate and there were 4 replicates for each treatment. Second, we are using an insecticide bioassay to monitor changes in susceptibility to insecticides before and at the end of each rotation modules. The difference in susceptibility before and after each application is being used to determine if susceptibility to a given insecticide is shifting in populations exposed to a given module. For each bioassay, 5 insecticide representing different chemistries and mode of action are being evaluated. For each insecticide, five to seven concentrations were tested that have mortality levels between 1 and 99% based on preliminary studies. Test the effect of concentration for each insecticide, we are using commercially formulated products diluted in distilled water on the day of testing. Before application, we found low to moderate resistance for thiamethoxam (RR = 5.25), imidacloprid (RR = 5.97), cyantraniliprole RR = 1.79) (RR=resistance ratio).  Third, we have been collecting samples beginning in March 23, 2020. Leaf samples have also been collected from each plot to determine the presence of Candidatus liberibacter asiaticus in the trees and determine the infection rate. When counts of ACP adults in any plot reach a previously defined threshold level, a spray has been applied within the insecticide rotation developed for that particular treatment. On April 21, 2020, the 0.2 ACP per tap treatment threshold was exceeded, and therefore on May 5, 2020, we applied dimethoate for one rotation scheme and fenpropathrin for the other. After application, the ACP populations in all areas that were treated decreased to low levels.  Finally, our goal is to investigate the correlation between the threshold ACP population level required to trigger a management spay within the context of effective insecticide resistance management. For each insecticide application, the insecticide mode of action, we are testing differences in population wide levels of acetylcholinesterase, nicotinic acetylcholine receptors, inhibitors of chitin biosynthesis, glutamate gated chloride channels, allosteric modulators, and voltage gate sodium ion channels. In this manner, we will develop an economical and sustainable management strategy for ACP with insecticides, which is still currently lacking in Florida. Our newly developed methods should have a positive impact on the management of Asian citrus psyllid populations by stabilizing or reducing resistance and increasing their economic viability.           

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