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.During this quarter, Prophyte treatments were applied to the Hamlin and Valencia sites in July and October. The root density and phytophthora counts for all treatments were done in August. Soil applied treatments were undertaken in late September and early October.In preliminarily reviewing the data, there were no significant differences among the root densities for Hamlin and Valencia. The range for Hamlin was 0.046 to 0.092 roots/ml of soil and for Valencia it was 0.02 to 0.072 roots/ml soil. There were no significant differences among the total phytophthora propagule count for the Valencia which ranged from 12.8 to 23.2 propagules/cm3 of soil. When separated for the species there was alss no difference. In the Hamlin trees, there was a significant difference among treatments. The Ridomil, Presidio, Phosphite, and Orondis treatment had no propagules and this was signficantly fewer than the Phosphite alternated with Ridomil treatment which had 19.2 propagules/cm3 of soil. In both sites, there was a significant block effect and a new statistical analysis will be needed to take this factor into account. No brown rot measurements were taken this year.Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesAs planned in the proposal, this objective awaits this years yield results to begin calculating benefit-cost based on a combination of change in yield from the previous year and comparison among treatments within blocks.