Blueberry production in Mississippi (MS) is mainly rabbiteye blueberries (Vaccinium virgatum Ait.), which ripen in late May to June. Growing early-ripening southern highbush blueberries (SHBs) (Vaccinium corymbosum L.) presents an opportunity for early fruit production and increased market price for locally produced blueberries, yet faces the challenge of spring frost damage. One-year-old liners of 10 SHB cultivars were transplanted into 15-gallon plastic containers and placed in a high tunnel in Apr. 2015. Blueberry plants were fertilized with either a conventional or an organic fertilizer at comparable rates. Plants were evaluated for berry yield, timing of first berry harvest and peak harvest, single berry weight, and soluble solid content during the 2016 and 2017 growing seasons. The high tunnel increased monthly maximum temperature by 3.2 to 10.4 °C, monthly average temperature by 0.7 to 4.2 °C, and minimum monthly temperature for up to 3.0 °C compared with outdoor environment. Photosynthetically active radiation (PAR) at noon in the high tunnel ranged from 477 to 1411 µmol·m−2·s−1 and relative humidity ranged from 54.6% to 81.7% from Jan. 2016 to June 2017. SHBs in the high tunnel produced first berry harvest during the first week of April in both growing seasons. Total berry yield per plant ranged from 921 g to 2136 g in 2016 and from 1222 g to 2480 g in 2017. Compared with the organic fertilizer, conventional fertilizer increased berry yield in April and May, and total berry yield in 2016, but resulted in similar yield in 2017. Eight cultivars (Emerald, Farthing, Gupton, Meadowlark, Pearl, Rebel, Star, and Sweetcrisp) produced single berries that averaged more than 2 g per berry in 2016, compared with two cultivars (Gupton and Pearl) in 2017. Smaller berry size may have resulted from the generally increasing yield from 2016 to 2017. ‘Sweetcrisp’ produced berries with higher soluble solid content, 14.2% and 14.1% in 2016 and 2017, than the other nine cultivars. Container production of SHB cultivars in a high tunnel produced total berry yield equivalent to 6458 kg/ha in 2016 to 7500 kg/ha in 2017, advanced blueberry production by 4 to 5 weeks, and therefore may serve as a potential production system for early fruiting blueberries in Mississippi.
Tongyin Li and Guihong Bi
Guihong Bi and Carolyn F. Scagel
In two separate experiments, Hydrangea macrophylla (Thunb.) Ser. ‘Merritt's Supreme’ plants were used to study the effects of foliar sprays of Def 6 (tributyl phosphorotrithioate, 2500, 5000, 7500, and 10,000 mg·L−1), gibberellic acid (GA, 50 mg·L−1), copper–EDTA (CuEDTA, 0.5% and 1.0%), Florel (2000 mg·L−1), and urea (3%) on defoliation in the fall and growth and flowering performance during forcing. Compared with controls (plants sprayed with water only), spraying plants with urea or GA alone had no influence on defoliation or plant performance during forcing, and spraying plants with Florel alone had no influence on defoliation but decreased total flower dry weight during forcing. Combining urea with Florel sprays decreased the adverse effects of Florel on plant quality and combining GA with Florel improved defoliation. Increasing concentrations of Def 6 and CuEDTA increased defoliation. Compared with controls, plants sprayed with CuEDTA exhibited more defoliation, showed bud and leaf necrosis, and produced lower flower dry weight during forcing. Combining urea with CuEDTA sprays decreased the adverse effects of CuEDTA on plant quality. Compared with controls, spraying plants with Def 6 increased defoliation, caused no visible damage to plants, and had no adverse effects on plant quality during forcing. Adding urea to sprays containing Def 6 decreased or had no influence on the efficiency of defoliation and increased total flower dry weight during forcing compared with Def 6 alone. Adding GA to sprays containing lower concentrations of Def 6 (2500 and 5000 mg·L−1) increased the efficiency of defoliation without adversely influencing plant quality.
Guihong Bi and Carolyn F. Scagel
Rooted liners of Hydrangea macrophylla (Thunb.) Ser. ‘Berlin’ were fertigated with different rates of nitrogen (N) from July to Sept. 2007 and leaves were sprayed with 15N-labeled urea in late October to evaluate urea uptake and 15N translocation by hydrangea leaves in relation to plant N status. Four plants from each N fertigation rate were harvested before they were sprayed with urea and 2, 5, 10, and 15 days after urea spray. Increasing rate of N fertigation increased plant N content in October before being sprayed with urea. Leaves rapidly absorbed 15N from urea spray. The highest rate of 15N uptake occurred during the first 2 days after urea spray and then decreased. Export of 15N from leaves occurred rapidly after uptake and the highest rate of 15N export occurred during the first 2 days after urea spray and then decreased. During the first 5 days after urea spray, the rate of 15N uptake by leaves and export from leaves decreased with increasing rate of N fertigation. On a whole plant basis, the total amount of 15N from foliar 15N–urea spray increased with increasing rate of N fertigation; however, the percentage of 15N exported from leaves and the percentage of N that derived from foliar 15N–urea spray decreased with increasing rate of N fertigation. Results suggest that hydrangea plants with lower N status in the fall are more efficient in absorbing and translocating N from foliar urea than plants with higher N status.
Amir Rezazadeh, Richard L. Harkess, and Guihong Bi
Red firespike (Odontonema strictum) is an ornamental shrub with potential for use as a flowering potted plant due to its dark green foliage and attractive red flower spikes. To stimulate branching and improve quality of red firespike, foliar spray applications of dikegulac sodium (DS) and benzyladenine (BA) and hand pinching were evaluated across two seasons (Spring and Summer 2014). There were three pinching treatments: one, two, or three pinches. Plant growth regulators (PGRs) were applied at 400, 800, 1600, or 2400 ppm DS or 600, 1000, 1250, or 1750 ppm BA. Both studies included an untreated control. Red firespike treated with all concentrations of BA and 1600 and 2400 ppm DS had increased branching compared with the control, except 1000 ppm BA in Expt. 1. Pinching did not affect the number of branches. Dikegulac sodium at 1600 and 2400 ppm and all concentrations of BA resulted in shorter plants than the control. Phytotoxicity was observed in plants treated with 1600 or 2400 ppm DS. In both experiments, DS at 1600 and 2400 ppm had the least plant dry weight compared with the control. Treatment with BA at 1750 ppm resulted in greatest leaf area compared with control. Dikegulac sodium at 800 ppm increased the number of flowers compared with control. Pinching and BA did not affect number of inflorescences. All concentrations of BA and DS delayed flowering, except 1000 ppm BA. Plants treated with 800, 1600, and 2400 ppm DS had shorter inflorescences compared with control plants. Benzyladenine decreased the length of the inflorescence at high concentrations, 1250 and 1750 ppm. Pinching treatments did not affect inflorescence length.
Diana R. Cochran, Amy Fulcher, and Guihong Bi
Pruning is commonly performed during production of nursery crops to produce symmetrical, compact plants that are pleasing to the consumer’s eye. To achieve the desired results, nursery growers hand prune or apply plant growth regulators (PGRs). However, hand pruning is expensive and is not always effective, and efficacy of PGRs can depend on cultural practices, environmental conditions, irrigation, cultivar, and rate. Therefore, the objective of these experiments was to evaluate the effect of dikegulac sodium applied to pruned or unpruned ‘Limelight’ hardy hydrangea (Hydrangea paniculata). Plants were grown at two locations, Tennessee (TN) and Mississippi (MS). The pruned treatment consisted of hand pruning, leaving three nodes followed by applications of dikegulac sodium (400, 800, or 1600 ppm). Applications of dikegulac sodium to pruned or unpruned plants were made the same day using a carbon dioxide backpack sprayer. There were two additional control treatments: hand-pruned untreated (hand-pruned) and unpruned untreated (untreated). Plants were grown outdoors under full sun in TN and under 40% shade in MS. Data were collected at the close of the experiment on the number of branches over 1 inch, final growth index (FGI), floral attributes, branch symmetry, and phytotoxicity. At both locations, pruned and unpruned plants treated with 800 or 1600 ppm dikegulac sodium had more branches than the hand-pruned and unpruned plants. Flower number and size tended to be greater for unpruned plants than pruned plants. Phytotoxicity was observed at 2 and 6 weeks after treatment (WAT). For plants grown in TN, symptoms were more pronounced on plants following treatment with 800 (pruned plants) and 1600 ppm (pruned and unpruned) dikegulac sodium compared with the untreated plants. There were no visible phytotoxicity symptoms at 6 WAT for plants grown in MS, regardless of treatment.
Tongyin Li, Guihong Bi, and Richard L. Harkess
Plant growth and nitrogen (N) uptake of Encore® azalea ‘Chiffon’ (Rhododendron sp.) grown in a traditional plastic container or a biodegradable container made from recycled paper were investigated over the 2013 growing season. Three hundred twenty 1-year-old azalea liners, grown in two types of containers, were fertilized twice weekly with 250 mL N-free liquid fertilizer with no N or 15 mm N from ammonium nitrate (NH4NO3). Biweekly from 10 May to 3 Dec., five plants from each N rate and container type were selected randomly to measure plant height, widths, and leaf chlorophyll content in terms of soil–plant analysis development (SPAD) readings, and were then harvested destructively for nutrient analyses. Leaf SPAD readings and tissue N concentration were influenced mostly by N rate rather than container type, with 15 mm N producing greater values than the no-N treatment. Leaf SPAD readings increased from May to August and decreased from September to December. Using 15 mm N, plastic containers generally resulted in similar or increased plant growth [plant growth index (PGI) and dry weight] and N uptake from May to August as in biocontainers, with greater SPAD readings, leaf and root dry weights, stem and root N concentrations, and leaf and root N content than biocontainers at some harvests. However, biocontainers resulted in greater PGI, dry weights, and N content (in leaves, stems, roots, and total plant) than plastic containers later in the season, from September to December. These differences appeared in September after plants grown in plastic containers ceased active growth in dry weight and N uptake by the end of August. Plants grown in biocontainers had extended active growth from 13 Sept. to 9 Nov., resulting in greater tissue N content and greater N uptake efficiency. The biocontainers used in this study produced azalea plants of greater size, dry weight, and improved N uptake by increasing growth rate and extending the plants’ active growth period into late fall. The beneficial effects likely resulted from greater evaporative cooling through container sidewalls and the lighter color of the biocontainers, and therefore led to lower substrate temperatures and improved drainage.
Guihong Bi, Carolyn Scagel, and Leslie Fuchigami
One-year-old field-grown `Nonpareil'/'Nemaguard' and `Nonpareil'/`Lovell' almond nursery trees were used to study the effects of chemical defoliants (CuEDTA and ZnSO4) and foliar applications of urea on defoliation and nitrogen (N) reserves. Although both chemical defoliants significantly promoted earlier defoliation, CuEDTA was more effective than ZnSO4 in promoting early defoliation. Two applications of defoliant had a similar effect as one application on promoting leaf abscission. Foliar applications of urea in addition to defoliant applications (urea + defoliant treatments) generally increased the efficiency of ZnSO4 (1.25% to 2%) and CuEDTA (0.5%) in promoting early defoliation. Although treatments with only defoliants did not consistently lower N reserve levels, trees treated with foliar urea or urea + defoliants had significantly higher nitrogen reserves compared to trees receiving only defoliant treatments. N reserves were comparable in urea + defoliant-treated trees to the levels found in naturally defoliated (control) trees. We conclude that both CuEDTA and ZnSO4 are effective in promoting early defoliation of almond nursery trees. Combining urea with defoliants can effectively promote early defoliation and is important for achieving N reserves similar to naturally defoliated trees.
Amir Rezazadeh, Richard L. Harkess, and Guihong Bi
This study evaluated the effects of paclobutrazol (PBZ) and flurprimidol on the morphological and physiological characteristics of potted red firespike (Odontonema strictum) under drought stress. PBZ and flurprimidol were applied as a soil drench at 0.24 mg/pot. Untreated plants acted as a control. The plants were exposed to drought stress 2 weeks after plant growth regulator (PGR) application. Another group of plants treated with PGRs was watered regularly. A reduction in plant height, plant diameter, and growth index (GI) was observed in plants treated with PGRs and drought stress 5 weeks after beginning the study. Drought stress reduced plant height by 45% compared with control. Flurprimidol under drought stress decreased plant diameter and GI by 36% and 76%, respectively, compared with the control. The least leaf area and plant dry weight were observed in plants drenched with flurprimidol and grown under drought stress. Drought stress also delayed flowering and the number of plants flowering. Plants treated with PBZ had the highest photosynthesis rate, 54% more than untreated plants under drought stress alone. The lowest stomatal conductance (g S) was measured in plants under drought stress alone or drought plus PBZ. Application of PBZ-enhanced red firespike drought tolerance reducing adverse effects of water stress on photosynthesis during the experiment.
Amir Rezazadeh, Richard L. Harkess, and Guihong Bi
The effect of plant growth regulators (PGRs) on growth and flowering of potted red firespike (Odontonema strictum) were examined in two experiments. In Expt. 1, foliar spray applications of daminozide, uniconazole, paclobutrazol, or flurprimidol or media drenches of paclobutrazol or flurprimidol were applied. In Expt. 2, foliar spray application of daminozide or media drenches of paclobutrazol or flurprimidol were further tested for efficacy of height control. Both studies included an untreated control. In Expt. 1, drench applications of paclobutrazol and flurprimidol resulted in plants 65% or 46% to 62% shorter than control, respectively. Paclobutrazol and flurprimidol drenches also decreased overall plant growth by 81% to 88% and 74% to 84%, respectively, compared with the control plants. PGRs did not affect number of inflorescences; however, paclobutrazol and flurprimidol delayed flowering 23 to 31 days. In Expt. 2, plants treated with flurprimidol or paclobutrazol drenches were shorter than the control. The greatest reduction in total plant growth occurred using a flurprimidol drench at 0.47 mg/pot, which resulted in plants 78% smaller than the untreated control. Paclobutrazol and flurprimidol increased the time to flowering 11 to 27 days and 10 to 26 days, respectively. The most attractive and well-shaped plants were achieved with flurprimidol applied at 0.24 mg/pot or applications of paclobutrazol at 0.35 mg/pot.
Ritu Dhir, Richard L. Harkess, and Guihong Bi
The development of bleaching of the youngest leaves of actively growing ivy geranium (Pelargonium peltatum) has been observed as the season progresses from late spring to summer. Cultivar differences in foliar bleaching in response to elevated air temperature were studied. Ivy geranium ‘Beach’ and ‘Butterfly’ were grown in media containing sphagnum peat and perlite (70:30 v/v) for 6 weeks in modified greenhouse chambers with air temperatures averaging 28/16 or 36/22 °C (day/night). ‘Beach’ had greater plant width, growth index, leaf area, total fresh weight, and total dry weight than ‘Butterfly’ regardless of temperature. Overall, elevated air temperatures severely reduced plant width, plant growth index, leaf area, fresh weight, and dry weight of ivy geraniums. Elevated air temperatures caused foliar bleaching in both cultivars; however, ‘Butterfly’ was more susceptible to bleaching than ‘Beach’. ‘Beach’ had higher chlorophyll (Chl) b and total Chl content than ‘Butterfly’ at ambient air temperature, but they were similar at elevated air temperatures. Regardless of temperature, ‘Beach’ had greater Chl a, carotenoids (Caro), and pheophytins content but lower Chl a:Caro, Chl b:Caro, and total Chl:Caro ratios than ‘Butterfly’. This may contribute to the lower susceptibility to bleaching of ‘Beach’. Elevated air temperatures reduced Chl a, Caro, Chl a:Caro, Chl b:Caro, total Chl:Caro, and pheophytins content of ivy geraniums. In both cultivars, manganese (Mn) content increased with elevated air temperatures, but ‘Beach’ had greater Mn content than ‘Butterfly’. Total iron (Fe) content did not vary with cultivar or temperature. Irrespective of temperature, zinc (Zn) content was greater in ‘Beach’ than ‘Butterfly’, and irrespective of cultivar, Zn content was greater at elevated air temperatures. These results suggest greater chlorophyll, carotenoids, pheophytins, foliar Mn, and Zn contents play a role in reduced susceptibility of ‘Beach’ to foliar bleaching.