1. Please state project objectives and what work was done this quarter to address them: The overall goal of the project is to develop fertilization strategies to best match nutrient supply and demand, and develop recommendations for optimal nutrient application timing as compared to a simple constant supply, which will improve fruit yield, quality, and reduce fruit drop. Objective 1) Test if a reduced N-P-K nutrient supply in the fall is safe for sustaining HLB-affected citrus, and whether it can improve fruit quality to facilitate earlier maturity / harvesting and reduce fruit drop: We completed the second split fertilizer application for designated treatments in early April, allowing a comparison of leaf nutrients sampled on May 2 at the 25% and 50% annual fertilizer allocations. For the Hamlin experiment, leaf N concentrations were significantly higher in the 50% complete treatment (2.53% N) than the 25% complete treatment (2.38% N). Leaf K concentrations were also significantly higher (1.41% K) in the 50% complete treatment than the 25% complete treatment (1.23% K). For the Valencia experiment, only leaf N was significantly higher for the 50% treatment (2.55% N) than the 25% treatment (2.33%). There were no other significant differences in foliar nutrients between treatments at that time. There were however deficiencies of Mn, and low levels of Ca, Mg, Zn, Fe and B in the two experiments according to the leaf analysis of May 2. Leaf samples collected on May 29 were analyzed and indicated improved nutrient status, with only Ca and Zn deficiencies in the experiments. Leaf N concentrations for Hamlin and Valencia experiments remained significantly different for the 50% and 25% completed fertilizer treatments (Hamlin: 2.69%, 2.81% N for 25%, 50% complete; Valencia: 2.49%, 2.66% N for 25%, 50% complete). The third split fertilizer application was in early June but the leaf samples were not analyzed yet. Dry and hot spring weather extending well into late June seemed detrimental to the trees despite daily irrigation. Fruit diameter was measured at every two weeks starting from phase 2 of fruit development (end of May), at 8 fruits per plot. Although fertilizer was applied 3 times, there was not any significant increase in fruit growth between treatments, but there was significant different in fruit growth between Hamlin and Valencia. The second Aerobotics drone survey flew at the end of May to collect data on tree size and health. There were no significant differences among treatments yet.Objective 2) Develop an optimized, practical fertilizer timing management profile to boost fruit quality and reduce fruit drop for HLB-affected citrus based in part on the sigmoidal nutrient demand curve defined by four physiological growth phases (0=bloom/fruit set; 1=cell division; 2=cell enlargement; 3=maturation):Our investigations to use the intensity of leaf symptom expression to help determine foliar nutrition in the field with smartphone apps is focusing on Mn first. We showed that we could visually classify 10 classes of Mn deficiency severity (all in the deficient range of <18 ppm). The corresponding leaf Mn concentrations correlated linearly with the 10 classes. The challenge will be to detect not yet easily visible Mn deficiency symptoms so that early diagnoses can be made. We plan to repeat the process with N, Mg, Zn, and Fe deficiency symptoms.B) New developments: sub-objectives concerning the Sugarbelle trial focusing on solving the current fruit quality issues are progressing well. We applied the first replicated foliar spray treatments to Sugarbelle trees at the city block consisting of KNO3 and KH2PO4. Two more applications will go out this summer. The purpose of the sprays is to increase peel thickness and strength to avoid soft fruit, as well as to improve fruit size. C) Issues: We are still concerned about the low fruit set in the city block compared to previous years. The early bloom in January followed by a dry hot spring has stressed the trees considerably. 2. Please state what work is anticipated for next quarter:The third and fourth fertilizer applications will be made to designated treatment plots in July and September. Soil, lysimeter sampling, leaf sampling, processing and analysis will be ongoing, as will tree size and fruit measurement. The third Aerobotics drone survey will fly in late September or early October, to evaluate tree health and size indicators. 3. Please state budget status (underspend or overspend, and why):Spending rate is approximately on track, slightly less than expected due to startup lag in Q1.