We requested a NCE for this grant to allow proper completion of a promising greenhouse citrus root growth study that was repeated with Carrizo rootstock. This is part of objective 2 (Determine soil conditions that favor root hair and VAM proliferation) and does not affect the subawards and efforts of Vashisth, Wright and Morgan. We don’t anticipate any travel or field work. Objective 1: Leaf nutrient thresholds We implemented the full Diagnosis and Recommendation Integrated System (DRIS) method for leaf nutrient analysis that provides protection from cross-correlation of variables and environmental effects. Reference nutrient data for DRIS was obtained from high-yielding ‘Hamlin’ trees growing in the Ft. Meade area prior to HLB (>700 boxes/acre average). The DRIS method has proved very valuable for indicating ranges of critical deficiency for K, Mn, Zn, Fe. Mg, B, and Cu. Some nutrients, including S, N, Ca and P did not correlate well enough using DRIS to pinpoint critical thresholds, but general trends were still useful. These results look promising for publication and ultimately will be used to revise existing IFAS thresholds for citrus. We continue to analyze the large survey dataset from every angle and with new analytical tools since it contains an abundance of important information. Objective 2: Determine soil conditions that favor root hair and VAM proliferation The results so far with Carrizo look much better than the original root study which was using rooted scion (Murcott) material. In order to get the required information from the trial, we captured more SEM images to quantify root hair growth (Dec 2018). Visually the root hair growth was dramatically increased by tricalcium phosphate in equilibrium with the growing solution. We will quantify root hairs from the images in early 2019. When psyllid adults become available in February, we plan to inoculate the hydroponic citrus trees with CLas so that the impacts of infection and nutrient solution treatment can be measured in root hair growth (until about May 2019). The final report will be completed in May/June.