The central mission of this project is to combine existing fertilization, irrigation, scion and rootstock options in modern, high-density citrus groves that will be more productive sooner, and survive the onslaught of HLB more successfully than conventional Florida citrus groves. The resulting synergistic production system was called the Advanced Citrus Production System, and relied heavily on open hydroponics with liquid fertigation, and computer automation, as well as precocious, dwarfing rootstocks and high planting densities. The overall goals of this three-year project renewal are to continue the existing ACPS experiments at Auburndale (2.5 year old replant) and at the CREC (mature 20 year old ACPS retrofit) in order to obtain long-term data which is crucial for the successful recommendation and adoption of this technology. A demonstration ACPS experiment testing four different rootstocks was established in March 2011 on 5 acres of CREC’s Lake Placid grove, and will also be continued with this project. Finally, two new ACPS experiments will be established to fill gaps and to evolve the new ideas developing from our current research experiments. Specific objectives are: i) To install a ‘Valencia’ juice orange ACPS replant experiment at the CREC, testing two rootstocks (US897, Swingle), and two novel ultra-high planting densities with narrow grove equipment. ii) To install a grapefruit fresh fruit ACPS replant experiment in the Indian River region in order to adapt the technology for regional priorities, conditions and soil types. iii) To continue the existing ACPS experiments at Auburndale, CREC (Lake Alfred), and Lake Placid. The collective results from various ACPS experiments of this project were valuable in demonstrating to citrus growers the need for using higher planting densities and more intensive irrigation and balanced fertilization technologies in order to remain competitive in an HLB-endemic environment. Economic production in the young Hamlin experiment was achieved in the third year (220 boxes/acre), and a year later, reached full production at 622 boxes/acre), with the best combination of rootstock (C35), high density (363 trees/acre), and drip fertigation. Conventionally grown groves would typically reach full production only after 6-10 years. Unfortunately the HLB incidence in this grove grew rapidly, reaching 75% in the fifth year, and causing drastic yield decline of affected trees. The best yield obtained in the fifth year was only 436 boxes/acre, and continued to decline thereafter due to stunted tree canopies and root systems, low fruit set, small fruit size and excessive preharvest fruit drop. The recommended practice of HLB management by destroying HLB-affected trees was futile in this grove because it was surrounded by symptomatic dooryard citrus trees in neighboring properties, over which we had no control. Unfortunately the other trials in this study suffered similar early high HLB incidence rates, leading to unsustainable production scenarios. The new knowledge, and horticultural gains of tree growth and fruit yield made with the ACPS research in this project were remarkable, but were compromised by less successful psyllid control and HLB prevention practices. The outcomes and technologies of this research have been adopted by many Florida growers for replanting new groves, especially with higher densities, precocious rootstocks like C35, and using effective hydroponic fertigation through drip or microsprinkler irrigation systems. Ultimately when HLB-resistant rootstocks or varieties are developed and released, the new resistant groves can be established in the most efficient and rapid method possible by adopting ACPS techniques developed and tested in this project.