Field studies were conducted in 2011 and 2012 in Belle Glade, FL, to evaluate the critical period of weed control (CPWC) in snap bean grown on organic soils in the Everglades Agricultural Area (EAA) of South Florida. Treatments consisting of increasing duration of weed interference and weed-free period were imposed at weekly intervals from 0 to 7 weeks after emergence (WAE) of snap bean. The beginning and end of the CPWC based on 2.5%, 5%, and 10% snap bean acceptable yield loss (AYL) levels were determined by fitting log-logistic and Gompertz models to represent increasing duration of weed interference and weed-free period, respectively. Based on 2.5% yield loss, the CPWC was 7.2 weeks long, beginning 1.2 (cotyledon and unifoliate leaf) and ending 8.4 WAE (mid-pod set, 50% of pods reached maximum length). At 5% yield loss, the CPWC was 5.0 weeks, beginning 1.7 (first to second trifoliate leaf) and ending 6.7 WAE (mid-flower to early pod set, 50% of flowers open and one pod reached maximum length). At 10% yield loss, the CPWC was 3.0 weeks, beginning 2.2 (second trifoliate leaf) and ending 5.2 WAE (early flowering, one open flower). Based on these results, the beginning of CPWC was hastened, whereas the end was delayed at different yield loss levels showing that acceptable weed control in snap bean on organic soils in the EAA is required throughout much of the growing season to minimize yield loss.
Banded cucumber beetle [BCB (Diabrotica balteata)], serpentine leafminer [SL (Liriomyza trifolii)], and aphids (Homoptera: Aphididae) are among the major insect pests that cause significant economic damage to lettuce (Lactuca sativa) in southern Florida. Four romaine cultivars and three iceberg cultivars, currently used in Florida's lettuce production, were evaluated from Oct. 2010 to Jan. 2011 in separate field experiments for their responses to insect infestation. Lettuce cultivars differed significantly in their responses to infestations of BCB and aphids. Cultivar 70096 had the lowest percent (3.7%) of BCB feeding damage among the romaine cultivars. Romaine cultivar Manatee also had significantly lower BCB feeding damage (12.1%) than the susceptible cultivars Okeechobee (19.8%) and Terrapin (19.1%). The lowest level of infestation of aphids was observed on ‘Manatee’, followed by ‘70096’, whereas ‘Okeechobee’ and ‘Terrapin’ had severe infestation of aphids. The iceberg cultivars were similar to one another in their responses to BCB and SL but not in their response to aphid infestation. Yield was decreased from 3% to 37% for six of the seven cultivars grown under the adverse environmental conditions of insect infestations and cold weather in Dec. 2010, but the yield of ‘70096’ did not decline. The cultivars identified as resistant to insects can play an important role in integrated pest management (IPM), which may decrease pesticide application, reduce production costs, and protect the environment.
Essential nutrients for citrus [‘Bingo’ (Citrus reticulata, Blanco)] production are important for different functions, including photosynthesis, resistance to disease, and productivity. During the past 15 to 20 years, citrus production in Florida has significantly declined as a result of the devastating citrus greening disease also called huanglongbing (HLB). Therefore, a greenhouse study was conducted for 2 years, starting in 2018, at the University of Florida/Institute of Food and Agricultural Sciences Citrus Research and Education Center in Florida to evaluate the effect of varying rates of iron on the growth and development of 2-year-old HLB-affected ‘Bingo’ (Citrus reticulata, Blanco) trees on Kuharske citrange rootstock. Four treatments were used in a randomized complete block (HLB status) design with seven single tree replicates for each treatment. The treatments applied were 0.0 (control), 5.6 (standard fertilization, lx), 11.2 (2x), and 22.4 (4x) kg⋅ha−1 iron on HLB-affected and healthy (non-HLB) citrus trees. Data including trunk diameter, tree height, and leaf samples were collected, processed, and analyzed at 3-month intervals for 2 years. At the end of the second year, trees were destructively sampled and processed as above-ground and below-ground biomass. Tree heights were different among iron rates of HLB-affected trees (P < 0.001); however, they were similar for non-HLB trees for both years. Higher average trunk diameters (P < 0.001) were observed for HLB-affected trees that received the 2x rate compared with the 1x rate and the control. In 2019, non-HLB trees showed 13% to 40% higher iron concentrations in leaves than HLB-affected trees. However, leaf iron concentrations were comparable for HLB-affected and non-HLB trees in 2020. Above-ground biomass for HLB-affected trees had between 33% and 44% more biomass (P < 0.01) than below-ground biomass for the corresponding iron fertilization. Iron accumulation correlated positively with all studied nutrients in the above-ground parts for both HLB-affected and non-HLB trees. A 95% confidence interval at which total biomass was nearly maximum corresponded to an iron rate of 9.6 to 11.8 kg⋅ha−1, which was close to the 2x rate. Therefore, soil iron application using the aforementioned rates may be appropriate for better growth and development of young HLB-affected trees.
Application of organic amendments can increase dissolved organic C (DOC) concentrations, which may influence movement of nutrients and heavy metals in soils. The objectives of this study were to investigate the influence of compost sources and application rates on concentrations of soil DOC, NO3-N, and extractable P over 29 months after a one-time application of compost to bermudagrass [Cynodon dactylon (L.) Pers.] turf. Few differences were evident between compost sources for soil total organic C (TOC), DOC, and NO3-N. However, the initial P content of compost sources significantly influenced soil extractable P. Increasing the rate of compost application increased soil TOC initially, but levels remained fairly stable over time. In contrast, DOC continued to increase from 3 to 29 months after application, suggesting that compost mineralization and growth of bermudagrass contributed to DOC dynamics in soil. Dissolved organic C was 98%, 128%, 145%, 175%, and 179% greater 29 months after application of 0, 40, 80, 120, and 160 Mg compost/ha, respectively, than before application. Rate of compost application had less effect on DOC than TOC, as DOC concentrations appeared controlled in part by bermudagrass growth patterns. Soil NO3-N was generally unaffected by compost application rate, as NO3-N decreased similarly for unamended soil and all compost treatments. Soil extractable P initially increased after compost application, but increasing the application rate generally did not increase P from 3 to 29 months. Seasonal or cyclical patterns of TOC, DOC, and extractable P were observed, as significantly lower levels of these parameters were observed in dormant stages of bermudagrass growth during cooler months.
Compost application to turfgrasses may contribute to accumulation of macronutrients in soil and eventually pose leaching and runoff hazards. The objectives of this study were to determine the influence of compost on soil-dissolved organic C (DOC) and accumulation of NH4OAc-EDTA-extractable and water-soluble nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) in St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf. Dissolved organic C increased from 3 to 29 months after application for unamended and compost-amended soils, indicating contribution from decomposition of both compost and St. Augustinegrass residues. Dissolved organic C was 75%, 78%, and 101% greater 29 months after application of 0, 80, and 160 mg·ha−1 of compost, respectively, than before application. Dissolved organic C and macronutrients exhibited considerable seasonal variation, because DOC and EDTA-extractable P, Ca, Mg, and S increased after compost application, whereas NO3 declined. Water-soluble K, Ca, and Mg declined, whereas P and S increased from 0 to 29 months. Similar seasonal changes in macronutrient concentrations occurred for unamended and compost-amended soil, indicating that composts, in addition to turfgrass residues, influenced DOC and macronutrient dynamics. Long-term nutrient accumulation occurred in compost-amended turfgrass, but seasonal dynamics were more related to the growth stage of turfgrass than compost. Formation of DOC-cation complexes appeared to contribute to macronutrient mobility, because decreases in DOC and nutrient concentrations occurred during turfgrass dormancy in winter and after high precipitation levels, indicating the potential for leaching of DOC-associated nutrients from soil.
Improving nutrient uptake and tree health play an important role in managing Huanglongbing (HLB)-affected citrus trees in Florida. A greenhouse experiment was conducted to evaluate the effect of increasing rates of manganese (Mn) on growth and development of sweet orange [Citrus sinensis (L.) Osbeck] trees at the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center in Lake Alfred, FL. Half the trees were graft-inoculated with the HLB pathogen and the remainder were used as the HLB-free (non HLB) control trees. Four rates of Mn (0.0 kg·ha−1 Mn (Control), 5.6 kg·ha−1 Mn (1x—standard rate), 11.2 kg·ha−1 Mn (2x—standard rate), and 22.4 kg·ha−1 Mn (4x—standard rate) were split applied quarterly to both sets of the trees in a completely randomized design. There were seven single tree replicates for each treatment. Response variables measured were trunk diameter, tree height, leaf Mn concentration, plus above- and belowground biomass. The accumulated Mn in leaf tissues significantly increased trunk diameter but did not affect tree height for both HLB-affected and non-HLB trees, the 2x rate had the maximum value for trunk diameter relative to the 4x rate. This study established a positive correlation between soil available Mn with Fe and Cu, but negative correlation with B and Zn. A strong correlation of −0.76, −0.69, and 0.65 was observed between soil Mn and B, Zn, and Cu, respectively, as compared with 0.49 with Mn and Fe. Among HLB-affected trees, the 2x rate gave the most belowground dry matter, which was 3% greater than the control and 5% greater than 4x. Aboveground dry matter had at least 30% more biomass than belowground matter among all treatments within HLB-affected trees. For small and medium roots, Mn accumulation increased with Mn application until 2x rate and decreased thereafter for HLB-affected trees. The results from our study showed an Mn rate of 8.9–11.5 kg·ha−1 Mn, as the optimum Mn level for young ‘Valencia’ HLB-affected trees in Florida.
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.
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.
Use efficiency of applied nitrogen (N) is estimated typically to be <50% in most crops. In sandy soils and warmer climates particularly, leaching and volatilization may be primary pathways for environmental loss of applied N. To determine the effect of N fertilization rate on the N use efficiency (NUE) and apparent recovery of N fertilizer (APR), a replicated field study with ‘BHN 602’ tomato (Solanum lycopersicum) grown in sandy soils under a fertigated plastic-mulched bed system was conducted using ammonium nitrate as the N source at four different rates (0, 150, 200, and 250 lb/acre). Spring tomato was followed by fall tomato in the same field, a typical cropping sequence in north Florida. Fertigation of N fertilizer was applied weekly in 13 equal doses for both seasons. The highest NUE was 12.05% (spring) and 32.38% (fall), and the highest APR was 6.11% (spring) for the lowest rate of N applied (150 lb/acre). In the fall, APR was unaffected by fertilizer N rates and ranged from 12.88% to 19.39%. Nitrogen accumulation in tomato plants were similar among the three N fertilizer rates applied (150, 200, and 250 lb/acre), though compared with no N fertilizer application, significant increases occurred. Whole plant N accumulation, NUE, and APR declined or remained similar when N rates increased above 150 lb/acre. Additionally, a regression analysis and derivative of the quadratic fresh yield data showed that yields were maximized at 162 and 233 lb/acre N in the spring and fall seasons, respectively.
The prevalence of Huanglongbing (HLB) in Florida has forced growers to search for new management strategies to optimize fruit yield in young orchards and enable earlier economic returns given the likelihood of HLB-induced yield reductions during later years. There has been considerable interest in modifying orchard architecture design and fertilizer and irrigation management practices as strategies for increasing profitability. Our objectives were to evaluate how different combinations of horticultural practices including tree density, fertilization methods, and irrigation systems affect growth, foliar nutrient content, fruit yield, and fruit quality of young ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] trees during the early years of production under HLB-endemic conditions. The study was conducted in Fort Pierce, FL, from 2014 to 2020 on a 1- to 7-year-old orchard and evaluated the following treatments: standard tree density (358 trees/ha) and controlled-release fertilizer with microsprinkler irrigation (STD_dry_MS), high tree density (955 trees/ha) with fertigation and microsprinkler irrigation (HDS_fert_MS), and high tree density with fertigation and double-line drip irrigation (HDS_fert_DD). Annual foliar nutrient concentrations were usually within or higher than the recommended ranges throughout the study, with a tendency for decreases in several nutrients over time regardless of treatment, suggesting all fertilization strategies adequately met the tree nutrient demand. During fruit-bearing years, canopy volume, on a per-tree basis, was higher under STD_dry_MS (6.2–7.2 m3) than HDS_fert_MS (4.3–5.3 m3) or HDS_fert_DD (4.9–5.9 m3); however, high tree density resulted in greater canopy volume on an area basis, which explained the 86% to 300% increase in fruit yield per ha that resulted in moving from standard to high tree density. Although fruit yields per ha were generally greatest under HDS_fert_MS and HDS_fert_DD, they were lower than the 10-year Florida state average (26.5 Mg·ha−1) for standard tree density orchards, possibly due to the HLB incidence and the rootstock chosen. Although tree growth parameters and foliar nutrient concentrations varied in response to treatments, management practices that included high tree density and fertigation irrespective of irrigation systems produced the highest fruit yields and highest yield of solids. Soluble solids content (SSC) and titratable acidity (TA) were lower, and the SSC-to-TA ratio was highest under STD_dry_MS in 2016–17, with no treatment effects on quality parameters detected in other years. Both drip and microsprinkler fertigation methods sufficiently met tree nutrient demand at high tree density, but additional research is needed to determine optimal fertilization rates and better rootstock cultivars in young high-density sweet orange orchards under HLB-endemic conditions in the Indian River Citrus District.