The third mass screen of germplasm for sting nematode tolerance in large sand-filled tanks was completed in January 2024. Sixteen rootstocks were compared by planting four replicates of each in each of 4 tanks (256 seedlings total) – two tanks infested with sting nematode and 2 that were not infested. The trial began in May and ran for 7 months, two months longer than the previous trials, to enhance the nematode pressure. The trial is noteworthy for comparing rootstocks created at USDA and UF to each other and to historical industry standards. Most of the rootstocks have been available for propagation for a number of years; however, only the historical industry standards were available for comparison the last time sting nematode tolerance was evaluated 4 decades ago. An initial trial in this project evaluated UF rootstocks, whereas USDA rootstocks were screened in the second trial. Here we look for differences among the rootstocks and for consistency with the previous trials. Nematode populations were evaluated, prior to plant recovery from tanks, finding more than 200 sting nematodes of all stages per 250 cm3 soil in each infested tank, and no nematodes were detected in non-infested tanks. Plants were carefully dug from tanks and photographed after soil was rinsed from roots. They were then separated (top, tap roots, fibrous roots), dried for 72 h at 70oC, and weighed. Roots appeared abnormally thickened when damaged heavily by the nematode which may mask differences if measured exclusively by mass (Fig 1). A rating system (1-10) was used to assign a score to each plant within a rootstock, relative to the best plant(s) (given 10) in the non-treated group of that rootstock. Each rootstock was assigned a tolerance index T, where T= mean rank of 8 infested plants/mean rank of 8 non-infested plants. Three investigators rated the plants independently, the T rankings were highly significantly correlated, and were averaged. Fig. 2 shows these subjective ratings (Tsubj)plotted against tolerance estimated as the mean fibrous root weight from infested tanks/mean fibrous root weight from non-infested tanks (Twt). Tolerance of the rootstocks was surprisingly similar within 1) those used historically, or 2) produced by USDA or 3) by UF. The four historical standard rootstocks had low T values measured visually or by mass suggesting that most newer releases confer some tolerance to the nematode. While USDA rootstocks tended to have higher Tsubj values than historical standards, this was not the case for Twt. UF rootstocks tended to have the most tolerant lines according to both measures. The results of the trial were consistent with previous results and field observations. Kuharske which is widely used for burrowing nematode control was heavily damaged by sting nematode in a 3-year trial to evaluate cover crops and nematicides. Swingle citrumelo was rated as susceptible to sting nematode in previous surveys. In this and our previous tank trial using USDA rootstocks, US812 and US942 and US1516 outperformed sweet orange or sour orange. Similarly, in this and the previous trial using UF rootstocks, UF1, UF5 and Orange 16 had the highest Tsubj and Twt scores. There were discrepencies, however, such as LB8-9xS13-15-16 which performed poorly in the first compared to this trial. The very small plant size of LB8-9xS13-15-16 compared to the better performing rootstocks may make relative differences between infested and non-infested plants more difficult to measure accurately. The rootstock screening trials have provided consistent evidence that newer rootstocks are somewhat more tolerant under these conditions than the previous generation of commonly used rootstocks. The widespread occurrence of sting nematode in Florida may be a factor driving grower adoption of newer rootstocks. This is somewhat encouraging; however, there is no evidence in these trials that an acceptibly tolerant citrus cultivar has been identified. We shall continue screening new cultivars with Kuharske and UF5 as standards for intolerance and tolerance, respectively.