Objective 1 – Determine the effect of the ratio and concentration of Fe2+ + organic acid on hydroxyl radical production and stability. Objective complete. Objective 2 – Determine the phytotoxic levels of Fe2+ + organic acid solutions on citrus. Objective complete. Objective 3 – Determine the effect of Fe2+ + organic acid solutions on HLB titer using a rapid greenhouse, HLB-infected citron, rooted shoot bud assay. Continuing work to develop a rapid greenhouse screening system. Current systems are not yet ready for screening methods to cure or manage HLB. No CRDF funds being used for this research. Objective 4 – Requires screening system – see objective 3 discussion.Objective 5 – Requires screening system – see objective 3 discussion. Objectives 6 and 8 (Note: there is no 7) – These are the field tests for the various ferrous iron (Fe2+) and citric acid treatments on HLB status and horticultural measures for both mature (HLB symptomatic) and nonbearing (non-symptomatic) trees. Throughout this quarter (Oct. 1 – Dec. 31) as well as the project timeline, conventional pesticide spray applications were applied to all the treatments in the trial and were based on scouting and were in accordance with IFAS guidelines. Similarly, irrigation events were made based on tree and field conditions as determined by soil feel and appearance, tensiometer readings, water table observation well measurements and visual assessment of tree canopy. Fertilizer applications were made via fertigation and were `spoon fed’ with frequent small applications bi-weekly. No dry fertilizer was used. All 7 experimental treatments were applied to the trial block as per the protocol. There were three cold fronts that impacted the trial location in Indian River County during late Nov. through Dec. that were documented to be below 40. F. Significant leaf drop occurred 5-7 days after the cold weather but there was no treatment effect observed based on visual assessment of extent of abscission. Also, HLB leaf symptoms were prominent throughout the trial in late Dec. and will be visually assessed next quarter. A ground application of herbicide was made, and plant material was removed in preparation for a UAV flight for aerial imagery data collection. Aerial images were taken with a UAV equipped with a 20 MP digital camera on 12/31/2020. A set of overlapping images were taken at two altitudes – 100 and 150 feet. Images taken at 100 feet are for photo-documentation (0.36 inch/pixel) of the experiment and will be made available at the completion of the project. Images taken at 150 feet (0.53 inch/pixel) were processed by segmenting the image into trees and background using machine learning image analysis. Once the trees were segmented (identified and separated from the background), various measures were made/calculated including canopy area, density, perimeter, convex hull area and perimeter, and minimum and maximum caliper diameters. These measures, as well as the ground measures, will be correlated (statistical analysis) with the iron treatments to determine their effects. One additional set of images, including a photo-documentation set, will be collected at the end of the project.