Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

Report Date: 12/19/2022
Project: 19-010   Year: 2023
Category: Horticultural & Management
Author: Megan Dewdney
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them: HLB is known to make citrus roots more susceptible to Phytophthora root rot.  It also reduces the efficacy of chemical management of Phytophthora root rot, creating a difficult management scenario.  Current Phytophthora management recommendations are based on pre-HLB work done in the 1980s.  These three conditions raise the question of whether yield improvement from Phytophthora management is enough to pay for the management costs themselves.  The goal of this project is to develop new soil propagule density managment thresholds and recommendations for chemical management of Phytophthora root rot based on ecomonic analysis of yield responses in different soil conditions.  Objective 1) Determine if labelled Phytophthora management maintains efficacy in the field on HLB-affected trees for reducing fibrous root loss and improving yield. In this quarter, we collected root samples from the Felda area grove.  The root density was measured and the raw data appear to show that some treatments have greater density than the control for the Hamlin oranges.  There is much more variation in the Valencia plots and the trends are unclear.  Trends are also unclear from the populations of the two phytophthora species.  We have been working on the analysis of these plots and are reworking the analysis to use time as a factor.  We have harvested one of the hamlin sites and have the second site scheduled with the grower for the first week of January.  The fruit quality and size data have been gathered but not yet entered into the computer.  Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesThe co-PI responsible for the economic analysis of this project, asked to have their funds returned.  I am not sure whether they will provide an analysis of this project. 2. Please state what work is anticipated for next quarter:  The second Hamlin harvest.  The Valencia harvests and spring applications of the treatments.  Data analysis will continue to confirm whether there any treatment differences in yeild, fruit quality, root density, or inoculum levels of phytophthora.   3. Please state budget status (underspend or overspend, and why): The budget is underspent because when I took over the project, there had not been staff appointed to the project for several months.  This caused funds not to be spent in a timely manner.  Also I had been planning to ask for the no cost extension so that we could harvest the Valencia plots so I needed to make sure there were funds available for that purpose.   


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