2017 ASHS Annual Conference

Citrus production under protected environments can reduce huanglongbing (HLB) disease incidence and damage by excluding the Asian Citrus Psyllid vector. Our objectives were assess the ability of covered structures to reduce HLB incidence and determine the yield ability of container-grown ‘Ray Ruby’ grapefruit (Citrus paradisi) at super-high planting densities relative to in-ground open-air trees. We tested two production systems (screenhouse and open-air), two planting systems (in-ground and potted) and two rootstocks {‘Sour orange’ [C. aurantium] and ‘US897’ [Cleopatra (C. reticulata) × Flying Dragon (Poncirus trifoliata)]}. The experimental design was a RCBD split-split-plot with four replications. Production systems were allocated as the main plot, and planting systems and rootstocks as sub-plots. Trees were planted in Sept/2013 on a density of 1,957 trees/ha (total 896 trees/0.46 ha). Irrigation was performed on-demand using two 7.6-LPH drip emitters per tree, and fertigation was applied three times/week using 15N-2.6P-22.4K water soluble fertilizer at 180 kg N/ha. Foliar nutrients, insecticides and fungicides were sprayed following standard practices. We monitored psyllids, leaf minors and other citrus pests monthly. There were no psyllids detected in the screenhouses, and 13.5 adults per plot in the open-air (p<0.0001). The in-ground trees had 110% more psyllids than potted trees (p=0.0134). HLB diagnosis indicated no disease in the screenhouses and fast disease progression in the open-air, with 100% infection in Mar/2017. No HLB differences were detected between in-ground vs potted nor ‘Sour orange’ vs ‘US897’ (p>0.05). Trunk diameter increased over time, and was 38% larger in-ground compared to potted. Canopy volume was 91% larger in the screenhouses compared to open-air, and 208% larger in-ground compared to potted (p<0.0001), with no rootstock effect. Leaf macro and micronutrient concentrations were influenced by treatment and sampling date. Fruit diameter was 12% smaller in 2015 than 2016. The screenhouses resulted in 77% more fruit and 22% larger fruit than open-air, and yielded 287 boxes with 38.5 kg/ha compared to 138 boxes in the open-air. Potted trees produced 17.5% less fruit than in-ground (p<0.0001). Yield was not influenced by planting systems or rootstocks (p>0.05). Fruit weight and diameter, juice weight and volume, and total solids/ha were 34% higher in the screenhouses. The open-air resulted in 19% higher titratable acidity, with 10.9 ratio in the screenhouses and 8.6 in open-air (p<0.0001). The screenhouses were promising for disease exclusion, and increased fruit yield and quality. However, the technology cost still under evaluation, in particular in areas subjected to inclement weather.