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 (Jan 1 – Mar 31) as well as the project timeline, conventional pesticide spray applications for non-bearing grapefruit trees 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 was one cold front that impacted the trial location in Indian River County on 02/04/2021 with a low temperature documented at 35.97 . F. Only very minor leaf drop occurred 5 days after the cold weather. Rainfall over this quarter was 5.79 in. with on 0.33 in. recorded in March 2021 requiring frequent irrigation events. Visual assessments of tree condition were made on 01/14/21 using a numerical rating of 1-4 for each tree quadrant and were averaged for each tree. Other field measurements included fruit counts (01/28/2021) and trunk caliper measurements (03/31/2021). Leaf sampling for PCR analysis was performed on 01/27/2021. As in prior quarters, a ground application of herbicide was made, and plant material was removed in preparation for a 03/06/2021 UAV flight to collect aerial imagery for canopy area determinations. Aerial images were taken with a UAV equipped with a 20 MP digital camera on 3/6/2021. A set of overlapping images were taken at two altitudes – 75 and 150 feet. Images taken at 75 feet are for photo-documentation (0.27 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.