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.No further phytophthora counts have been taken from the southwest Florida site this quarter. Treatment applications were made in early May in both the Hamlins and Valencia.We initiated a second location for two new trials, early oranges and Valencia in the Wachula area. The sites have a history of phytophthora. The preliminary counts from the blocks varied between 40 and 128. The per plot data in the early cultivars are high, varying between 15 and 120 CFU/plot with a fewplots with counts at 10 or below CFU/plot. In our Valencia block, we were suprised to find very low counts in many plots after our composite samples had at least 40 CFU in the block. We are not sure if there was a difference in trees sampled or if there was some sort of seasonal decline of the population because of the local block conditions. Objective 2) Determine benefit-cost thresholds for Phytophthora treatment on HLB-affected treesWe are waiting for more data