Field variety trials are a simple but effective tool to test plant horticultural performance under different environmental conditions and enhance the commercial adoption of new cultivars. Large-scale, rapid implementation of HLB-tolerant cultivars depends on reliable data, and the Millennium Block project is addressing the need of establishing field plantings to generate regional, updated information for the Indian River Citrus District. The project has two objectives: (i) Assess performance of new grapefruit cultivars with certain rootstocks under HLB endemic conditions in the IR district and (ii) ) Evaluate the influence of UFR and other recent rootstocks on grapefruit, navel, and mandarin in the IR in comparison to legacy/standard rootstocks. Trials tested: T1) grapefruit cultivars on three rootstocks, T2) 38 rootstocks with Ray Ruby grapefruit as the scion, T3) 36 rootstocks with Glenn 56-11 navel orange, and T4) 36 rootstocks with UF-950 mandarin.
We planted approximately 3,600 trees (Sep/19) and are waiting for the remaining trees to be delivered by the nursery (Summer/20). Masters student started on Jan/2020. Slow release poly coated fertilizer applied in Sep/19, Jan and May/20. Irrigation controller, sand media filtration system and water flow meter were installed. We applied imidacloprid to prevent leaf minor and psyllids, and followed with a spraying schedule as suggested by the certified crop advisor. The grove has been continuously scouted for pests such as psyllids, orange dogs and ants. Hoop boom was modified to spray young trees with higher accuracy, reducing the waste of agrochemical products. We created a tree location map and began production and distribution of QR tags to be used with scanner codes during data collection in the field. The group met with the certified crop advisor to develop a spray program schedule based on time of year and conditions to be applied as determined by IPM scouting.
Tree height, tree width in two positions (E-W and N-S), and trunk diameter were measured in three central trees from each experimental plot in Feb/20, and canopy volume calculated. Data only reflects the first 5-6 months of growth. On T1, ‘Pummelette UF-5-1-99-2’ on US-942 was 4x larger (0.2 m3) than ‘Start Ruby Gft DPI-60’ on X639 (0.05 m3) (P<0.0001). On T2, 'Ray Ruby Gft CGIP-103' on A+VolkxOrange 19-11-8 was ~3x larger (0.22 m3) than on UFR-17 (0.08 m3) (P<0.0001). On T3, 'Glenn Navel F-56-11' on 2247x6070-02-2 was ~5x larger (0.25 m3) than on Willets (0.04 m3) (P<0.0001). On T4, 'Mandarin UF-950' on US-897 was ~5x larger (0.25 m3) than on WGFT+50-7 (0.04 m3) (P<0.0001). Leaf samples for HLB diagnostic were taken from a pool of trees from each experimental plot and sent to the Southern Gardens lab, and all trees tested negative by May/20. Fruit phenology, pests and diseases have been monitored monthly. Canopy thickeness, canopy color and HLB incidence have been measured quarterly in all experimental plots.