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- Author or Editor: Bielinski M. Santos x
The response of young `Cartagena Ombligua' papaya (Carica papaya) plants to soil-applied copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn) was determined. Nursery experiments were conducted in the Dominican Republic, where Cu (0, 0.023, 0.046, 0.069, and 0.092 g), Mn (0, 0.27, 0.54, 0.81, and 1.08 g), Fe (0, 0.49, 0.98, 1.47, and 1.96 g) and Zn (0, 0.2, 0.4, 0.6, and 0.8 g per plant) were individually applied 20 days after transplanting. There were significant responses to the four elements. Maximum growth was obtained with 0.092 g Cu, 0.4 g Zn, 0.54 g Mn, or 0.98 g Fe per plant.
Greenhouse experiments were carried out to determine the tolerance of two radish cultivars to soil-applied B, Mo, and Zn. Sources used were boric acid (0, 54, 108, 216, 324, and 432 ppm), molybdic acid (0, 1.4, 2.8, 5.6, 8.5, and 11.3 ppm), and zinc sulfate (0, 40, 80, 160, 240, and 360 ppm) applied at planting in addition to the control. Plants were grown in plastic containers of 1.5 L, filled with a potting medium composed of 50% vermiculite, 30% sphagnum peat, and 20% perlite. Treatments were arranged within a randomized complete block design with six replications. Fresh weight of commercial roots was not affected by Mo or Zn applications in either cultivar. However, B applications decreased root fresh weight as rate increased. These results suggest that these radish cultivars perform well in a relatively wide range of Mo and Zn application rates, whereas tolerance to B appears to be low.
Field experiments were conducted in the Dominican Republic to determine the effect of combinations of N with folcysteine and gibberellic acid 3 on cilantro (Coriandrum sativum) yield. Nitrogen levels (0, 36, 55, 73, 91 kg·ha–1) in soil application at sowing were combined with foliar spray of the biostimulant folcysteine or gibberellic acid (0, 100, 200, 300, and 400 ppm) 15 days after emergence. Treatments were applied in a factorial arrangement on a randomized complete block design with three replications. Fresh weight of the aerial part of the plants was determined 40 days after emergence. No significant difference was found due to folcysteine treatment. Nitrogen had a significant effect, with optimal yield at 55 kg·ha–1. Significant interaction was detected for the combinations of gibberellic acid and N, with yield increasing as the rate of the two factors increased.
A study was conducted over two southern highbush blueberry (Vaccinium corymbosum × Vaccinium darrowi) seasons in a grower field in Florida. The objective was to compare the early fruit weight of southern highbush blueberry cultivars in high tunnels and in open fields. Four treatments were tested using combinations of two southern highbush blueberry cultivars (Snow Chaser and Springhigh) and two production systems (open fields and 18-ft-high tunnels). The results indicated that there was a significant effect of the production systems on the number of days with air temperatures at or near freezing (≤34 °F), and maximum and minimum air temperatures. The minimum air temperature in open-field plots reached ≈19 and 21 °F (61 freezing or near-freezing events) in the 2009–10 and 2010–11 seasons, respectively, whereas the minimum air temperatures inside the high tunnels were ≈32 and 33 °F, respectively, during the same seasons (only 3 days at ≤34 °F). This indicated that using high tunnels was an effective means to avoid freezing air temperatures in blueberries. In the first season, the cumulative early fruit weight was the highest in plots planted with ‘Snow Chaser’ inside the high tunnels (≈10 tons/acre), while the combined production of the two cultivars in the open fields did not reach 1 ton/acre until the end of the early harvests. The following year, there were no differences in the cumulative early fruit weight of both cultivars when planted in the open fields (2.2 tons/acre) and the cumulative fruit yields of ‘Springhigh’ and ‘Snow Chaser’ growing inside the high tunnels was twice and four times higher, respectively, than the early fruit production obtained in the open fields. These data showed the profound effect of high tunnels on flower protection and fruit set. High tunnels reduced water use for freeze protection. The total volume used in the open fields during the freezing or near-freezing days was ≈2.5 acre-inch/acre per 8 hours of freeze protection, whereas only 1/10 of that volume was applied inside the structures.
Field experiments were conducted in the Dominican Republic to determine the effect of gibberellic acid treatments on the elongation of the leading and lateral branches of `Hall' and `Semil-34' avocado (Persea americana) plants. The plant growth regulator was applied as a foliar spray to the leading branch at rates 0, 20, 40, 60, and 80 ppm. `Hall' avocado was not responsive to gibberellic acid treatment, whereas `Semil-34' was responsive, with higher rates inducing a more pronounced stem elongation. As an undesirable side effect, gibberellic acid treatment also stimulated the elongation of lateral branches in `Semil-34', making it unsuitable to enhance apical dominance on the leading branch.
The effect of three plant growth retardants, bitertanol, tradimefon, and hexaconazole, on short-term vine regrowth of pruned `Arabe' grape (Vitis vinifera) was studied in field experiments conducted in the Dominican Republic. Individual soil drench treatments of the three retardants were applied to adult pruned `Arabe' grape plants at rates 0, 0.25, 0.50, 0.75 and 1.00 g active ingredient per plant. Three weeks after treatment, bitertanol did not have a significant effect on vegetative growth, whereas triadimefon and hexaconazole caused significant reductions on vine regrowth. The effect of triadimefon as a growth retardant was stronger than that of hexaconazole, as described by regression equations Y = 30.88 - 25.68X for triadimefon, and Y = 32.9 - 15.2X for hexaconazole.
Field and container experiments were conducted in the Dominican Republic to determine the effect of gibberellic acid 3 (GA3) rates on papaya ringspot virus (PRSV)-infected seedlings and adult plants of `Cartagena Ombligua' papaya. The apical region of PRSV-infected and PRSV-uninfected plants was sprayed with GA3 aqueous solutions at rates 0, 25, 50, 75, and 100 ppm. PRSV-uninfected adult plants and seedlings produced longer internodes as GA3 rates increased. Adult PRSV-uninfected plants flowered normally at any GA3 rate. PRSV-infected seedlings and adult plants also responded to GA3 sprays, but to a lower extent. Typical symptoms of the disease were present in all the infected plants regardless of the GA3 rate applied, and adult plants did not flower at any rate. Results indicate that PRSV-infected `Cartagena Ombligua' papaya plants are responsive to exogenous GA3, although in a lesser degree than PRSV-uninfected plants. Linear regression equations described the effect of GA3 on the stem elongation of PRSV-infected and uninfected `Cartagena Ombligua' seedlings and adult plants.
Field experiments were conducted in the Dominican Republic to determine the effect of gibberellic acid (GA) and nitrogen (N) treatments on the growth of lateral branches in young `Keitt' mango plants. Two-year-old `Keitt' mango plants were pruned and treated with combinations of gibberellic acid (0, 20, 40, 60, 80, and 100 ppm) foliar sprays and soil nitrogen fertilization (18.75, 37.50, and 56.25 g). There were no N by GA interactions. Treatments did not significantly influence days to sprouting, number of sprouts, or number of leaves per sprout. N rates did not affect sprout length, whereas increasing GA rates enhanced sprout elongation. The effect of GA was described by the linear equation Y = 14.59 + 0.27X. Results indicate that GA sprays can be used to enhance sprout elongation to promote the desired round shape in canopies of `Keitt' mango plants.
Nitrogen (N) is the most growth-limiting for vegetable production in sandy soils. In Florida, current recommendations for preplanting N applications (100 lb/acre of N) in `Crookneck' summer squash (Cucurbita pepo) differ from those used by the growers (>200 lb/acre). Therefore, two field studies were conducted in Ruskin and Balm, Fla., to examine the effect of 50, 100, 150, 200, 250, and 300 lb/acre of N on summer squash growth and yield. Variables collected during this study were plant vigor (0–10 scale, where 0 = dead plant) at 3 and 7 weeks after planting (WAP), petiole sap nitrate-nitrogen (NO3-N) at 4 and 8 WAS, and marketable yield starting on 4 WAS (13 and 10 harvests in Ruskin and Balm, respectively). In Ruskin, plant vigor increased linearly with N rates, whereas there was no significant N effect in Balm. No differences in petiole sap NO3-N were observed in either location. In Ruskin, there was a rapid marketable yield increase (§25%) between 50 and 100 lb/acre of N, followed by no change afterwards. In contrast, there was no yield response in Balm. In the latter location, no crop had been established in the previous 3 years, enabling the soil to maximize its organic N accumulation (>40 lb/acre organic-N), whereas in Ruskin the experimental location had been continuously planted during the last three seasons (§25 lb/acre organic-N). The data demonstrated that organic N is an important source of the nutrient to complement preplant applications in summer squash.
Two field trials were conducted in Bradenton, Fla., to determine the effect of reduced methyl bromide plus chloropicrin (MBr + Pic 67:33 v/v) rates applied under two types of virtually impermeable films (VIF) on nutsedges (Cyperus spp.) and stunt nematode (Tylenchorhynchus spp.) control, and `Capistrano' bell pepper (Capsicum annuum) crop yield. MBr + Pic rates were 0, 88, 175, and 350 lb/acre. Mulch types were low-density polyethylene (LDPE) mulch, Hytibar VIF, and Bromostop VIF. Results showed that there were no differences on weed and nematode control, and bell pepper fruit yield between the two types of VIF. Two exponential models characterized the nutsedge responses to MBr + Pic rates with LDPE mulch and VIF, with weed densities declining as MBr + Pic rates increased. Reducing MBr + Pic rates by one-half (175 lb/acre) under VIF provided similar nutsedge control as the full-rate (350 lb/acre) with LDPE mulch. Similar results were observed with stunt nematode, where the most effective control occurred with VIF. Bell pepper yield with LDPE mulch responded linearly to increased MBr + Pic rates. However, a logarithmic model described the response of pepper yields to the fumigant rates under VIF. The application rate of this fumigant could be effectively reduced to 25% of the commercial rate (350 lb/acre) under either VIF, without causing significant bell pepper yield losses.