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  • Author or Editor: Brian Boman x
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A study was initiated in the 1997-98 production season to evaluate the effects of salinity on grapefruit yield and fruit quality in the Indian River area of Florida. The experiment was conducted on `Ray Ruby' grapefruit (Citrus paradisi) planted in 1990 on `Carrizo' citrange (C. sinensis × Poncirus trifoliata) and `Swingle' citrumelo (C. paradisi × P. trifoliata) rootstocks. Trees were planted on 15.2-m-wide (50 ft) double-row beds at a spacing of 4.6 m (15 ft) in-row × 7.3 m (24 ft) across-row [286.6 trees/ha (116 trees/acre)]. The control treatment was irrigated via microsprinkler emitters with water from a surficial aquifer well with an electrical conductivity (EC) of 0.7 dS·m-1. Higher irrigation water salinity levels were achieved by injecting a sea water brine mixture into the supply water to achieve ECs of 2.3, 3.9, and 5.5 dS·m-1. A wide range of rainfall and irrigation conditions occurred during the years encompassed by these studies, with rain totaling 1262, 1294, 1462, and 964 mm (49.7, 50.9, 57.6, and 38.0 inches) for 1997, 1998, 1999, and 2000, respectively. Salinity level had little effect on internal juice quality parameters [total soluble solids (TSS), acid, or juice content] at time of harvest. One of the most visible effects of irrigation with high salinity water was the damage to leaves, with leaf chloride (Cl) levels increasing about 0.14% for each 1.0 dS·m-1 increase in EC of the irrigation water for trees on `Carrizo' citrange and 0.02% for trees on `Swingle' citrumelo. For both rootstocks, the number of fruit and the size of the fruit decreased with increasing salinity in the irrigation water. The non-salinized trees had significantly larger fruit compared to the rest of the treatments. In the very dry 2000-01 season, trees on `Carrizo' irrigated with 0.7 dS·m-1 water had about 50% more fruit size 36 [fruit count per 0.028-m3 (4/5 bu) carton] or larger than trees watered with 3.9 or 5.5 dS·m-1 water. For trees on `Swingle' rootstock, trees irrigated with 0.7 dS·m-1 water had 150% to 200% more size 36 and larger fruit than trees watered with 2.3 dS·m-1 water. Over the four seasons, average yields for `Carrizo' were reduced 3200.0 kg·ha-1 (2855 lb/acre) per year for each 1.0 dS·m-1 increase in EC of the irrigation water. For `Swingle' rootstock, the reduction was 2600.3 kg·ha-1 (2320 lb/acre) per year for each 1.0 dS·m-1 increase in EC of the irrigation water. These reductions averaged 7% (`Swingle') and 6% (`Carrizo') for each 1.0 dS·m-1 increase in salinity of the irrigation water.

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Best management practices (BMPs) started in Florida citrus (Citrus spp.) in the 1990s and have evolved to play a major role in production practices today. One of the earliest BMPs in Florida arose from concerns over nitrate-nitrogen concentrations in some surficial groundwater aquifers exceeding the 10 mg·L-1 drinking water standard. This occurred in an area of well-drained sandy soils known as the Central Florida Ridge that extends north and south through the central part of the Florida peninsula. State agencies could have used a strictly regulatory approach and restricted how much nitrogen growers could apply. Instead of setting arbitrary regulations, the agencies promoted a scientific-based BMP approach. A nitrogen BMP for Central Florida Ridge citrus was established, and research is now validating the earlier groundwater work on more grower field sites. The purpose of this BMP was to minimize the risk of leaching nitrates from fertilizer into the groundwater. Several important aspects of the BMP involve: 1) limiting the amount of nitrogen fertilizer applied at any one time, 2) increasing the frequency of fertilizer applications, 3) reducing fertilizer applications during the summer rainy season, and 4) managing irrigation to reduce leaching below the root zone. Since this Central Florida Ridge nitrogen BMP was established, major BMP actions to improve water quality and reduce the quantity of runoff water have taken place in the Indian River production area of Florida's east coast. BMPs continue to be set up in other parts of the state for a variety of plant and animal agricultural practices. In some cases, cost-share funds have been provided to help implement BMPs. With voluntary BMPs, growers have scientifically based guidelines, a waiver of liability, and an avoidance of arbitrary regulations.

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Off-target deposition of pesticidal spray material is both an economic loss to the grower and a potential environmental problem in southern Florida. This study evaluated the reduction in non-target deposition of copper resulting from different approaches to spraying row-ends in typical Indian River citrus (Citrus) production systems. Using copper as a model pesticide, applications were made in a commercial citrus grove in June and July 2001. Non-target deposition on the water surface within an adjacent drainage canal, as well as on surrounding ground surfaces, was measured using Teflon spray targets. Specific row-end spraying scenarios included: 1) leaving both banks of nozzles on while turning; 2) turning the outside-facing nozzles off (leaving tree-facing nozzles on); 3) turning both banks of nozzles off at the tree trunk; and 4) turning all nozzles off at the end of the foliage of the last tree within the row. Deposition directly onto surface water contained within drainage canals was reduced significantly when nozzles were turned off at the last tree within a row, or when the outside-facing nozzles-only were turned off through the turn. Likewise, deposition was reduced on ground surfaces adjacent to the sprayer under the same scenarios. No differences were observed on ground surfaces on the opposite side of the canal. Significant reductions in direct application of agrichemicals to surface waters within Indian River citrus production groves can be achieved by turning nozzles off when turning from one tree row into the next.

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Although citrus (Citrus spp.) is sensitive to salinity, acceptable production can be achieved with moderate salinity levels, depending on the climate, scion cultivar, rootstock, and irrigation-fertilizer management. Irrigation scheduling is a key factor in managing salinity in areas with salinity problems. Increasing irrigation frequency and applying water in excess of the crop water requirement are recommended to leach the salts and minimize the salt concentration in the root zone. Overhead sprinkler irrigation should be avoided when using water containing high levels of salts because salt residues can accumulate on the foliage and cause serious injury. Much of the leaf and trunk damage associated with direct foliar uptake of salts can be reduced by using microirrigation systems. Frequent fertilization using low rates is recommended through fertigation or broadcast application of dry fertilizers. Nutrient sources should have a relatively low salt index and not contain chloride (Cl) or sodium (Na). In areas where Na accumulates in soils, application of calcium (Ca) sources (e.g., gypsum) has been found to reduce the deleterious effect of Na and improve plant growth under saline conditions. Adapting plants to saline environments and increasing salt tolerance through breeding and genetic manipulation is another important method for managing salinity.

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Six trials were conducted to determine whether lower spray volumes or inclusion of different surfactants would permit adequate thinning of mandarin hybrids (Citrus reticulata hybrids) at a much lower cost per hectare. Sprays were applied using a commercial airblast orchard sprayer during physiological drop when fruitlets averaged 8 to 16 mm in diameter. Surfactant was always included at 0.05% v/v. NAA always reduced fruit per tree, increased fruit size, and decreased production of smallest size fruit. However, in only three experiments, contrast of all NAA treatments vs. controls indicated increased production of the largest (80–100 fruit per carton) and most valuable fruit. In four of five experiments, comparison of spray volumes of 600 (only examined in three of four experiments), 1200, or 2300 L·ha–1 demonstrated significant fruit size enhancement from all NAA applications. Most individual NAA treatments resulted in fewer fruit per tree, but there were no statistically significant differences between NAA treatments at different spray volumes. In only one of the four experiments, there was a marked linear relationship between spray volume and fruit per tree, yield, mean fruit size, and production of largest fruit sizes. The effects of surfactants (Activator, a nonionic, Silwet L-77, and LI-700) on NAA thinning were tested in both `Murcott' and `Sunburst'. In comparisons between Silwet L-77 and Activator surfactant, one experiment with `Murcott' showed greater fruit per tree and yield reduction from using Silwet, but with a smaller increase in production of largest fruit sizes, whereas in another `Murcott' experiment, Silwet L-77 reduced numbers of smaller fruit size with no increase in production of larger fruit. Based on these findings, current recommendations for NAA thinning of Fla. mandarins are use of spray volume of ≈1100–1400 L·ha–1 on mature trees with proportionally lower volume on smaller trees. These data appear to support use of a nonionic surfactant rather than other tested surfactants in NAA thinning of Florida mandarins. Because experience with NAA thinning of Florida citrus is limited, it is only recommended where the disadvantages of overcropping are perceived to substantially outweigh the potential losses from overthinning.

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Rootstock significantly affected the development of stem-end rind breakdown (SERB) on `Valencia' and navel oranges (Citrus sinensis), but not `Ray Ruby' grapefruit (C. paradisi) or `Oroblanco' (C. grandis × C. paradisi), and affected postharvest decay on navel orange, `Ray Ruby' grapefruit, `Oroblanco' and one of two seasons (2002) on `Valencia' orange. In `Valencia' and navel oranges, fruit from trees grown on Gou Tou (unidentified Citrus hybrid) consistently developed low SERB. `Valencia' oranges on US-952 [(C. paradisi × C. reticulata) × Poncirus trifoliata] developed high levels of SERB in both years tested. Relative SERB of fruit from other rootstocks was more variable. Navel oranges, `Ray Ruby' grapefruit, and `Oroblanco' fruit from trees on Cleopatra mandarin (C. reticulata) rootstock consistently developed relatively low levels of decay, and in navel this level was significantly lower than observed from trees on all other rootstocks. In three of five trials we observed significant differences between widely used commercial rootstocks in their effects on postharvest SERB and/or decay. Given the expanding importance of sales to distant markets, it is suggested that evaluations of quality retention during storage be included when developing citrus rootstocks and scion varieties for the fresh market.

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Completely enclosed screen houses can physically exclude contact between the asian citrus psyllid [ACP (Diaphorina citri)] and young, healthy citrus (Citrus sp.) trees and prevent huanglongbing (HLB) disease development. The current study investigated the use of antipsyllid screen houses on plant growth and physiological parameters of young ‘Ray Ruby’ grapefruit (Citrus ×paradisi) trees. We tested two coverings [enclosed screen house and open-air (control)] and two planting systems (in-ground and container-grown), with four replications arranged in a split-plot experimental design. Trees grown inside screen houses developed larger canopy surface area, canopy surface area water use efficiency (CWUE), leaf area index (LAI) and LAI water use efficiency (LAIWUE) relative to trees grown in open-air plots (P < 0.01). Leaf water transpiration increased and leaf vapor pressure deficit (VPD) decreased in trees grown inside screen houses compared with trees grown in the open-air plots. CWUE was negatively related to leaf VPD (P < 0.01). Monthly leaf nitrogen concentration was consistently greater in container-grown trees in the open-air compared with trees grown in-ground and inside the screen houses. However, trees grown in-ground and inside the screen houses did not experience any severe leaf N deficiencies and were the largest trees, presenting the highest canopy surface area and LAI at the end of the study. The screen houses described here provided a better growing environment for in-ground grapefruit because the protective structures accelerated young tree growth compared with open-air plantings while protecting trees from HLB infection.

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Huanglongbing (HLB) disease is a threat to most citrus (Citrus sp.) producing areas and is associated with the bacterium Candidatus Liberibacter asiaticus. The disease is transmitted by the vector asian citrus psyllid [ACP (Diaphoria citri)]. Antipsyllid screen houses can potentially reduce and eliminate HLB development in young citrus plantings by excluding the insect vector. These structures are also anticipated to represent a new environmental platform to cultivate high-valued fresh citrus. The purpose of this investigation was to evaluate the effect of screen houses on excluding infective ACP from inoculating grapefruit (Citrus ×paradisi) trees and determine changes on environmental conditions caused by the screen cloth. We tested two coverings [enclosed screen house and open-air (control)] and two planting systems (in-ground and container-grown), with four replications arranged in a split-plot experimental design. Psyllid counting and HLB diagnosis were performed monthly, and the antipsyllid screen excluded the HLB vector from the houses. ACP and HLB-positive trees were found only at the open-air plots. Weather monitoring was performed every 30 minutes from 22 Feb. to 31 July 2014. Solar radiation accumulation averaged 6.7 W·m−2·minute−1 inside the screen houses and 8.6 W·m−2·minute−1 in the open-air. Air temperature was greater inside the screen houses whereas wind gusts were higher in the open-air. Reference evapotranspiration accumulation averaged 3.2 mm·day−1 inside the screen houses and 4.2 mm·day−1 in the open-air. There was no difference in cumulative rainfall between screen houses and open-air. The antipsyllid screen houses reduced solar radiation, maximum wind gust, and reference evapotranspiration (ETo). The environmental conditions inside the protective screen houses are suitable for grapefruit production.

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