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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.

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Guihong Bi, Carolyn F. Scagel, and Richard Harkess

Plants of Hydrangea macrophylla ‘Merritt's Supreme’ were fertigated with 0, 70, 140, 210, or 280 mg·L−1 nitrogen (N) from July to Sept. 2005 and sprayed with 0% or 3% urea in late October to evaluate whether plant N status during vegetative growth influences plant performance during forcing. In late November, plants were manually defoliated, moved into a dark cooler (4.4 to 5.5 °C) for 8 weeks, and then placed into a greenhouse for forcing. After budbreak, plants were supplied with either 0 N or 140 mg·L−1 N for 9 weeks. Plant growth and N content were evaluated in Nov. 2005 before cold storage and plant growth, flowering, and leaf quality parameters were measured in late Apr. 2006. Increasing N fertigation rate in 2005 significantly increased plant biomass by ≈14 g (26%) and plant N content by ≈615 mg (67%). Spray applications of urea (urea sprays) in the fall had no influence on plant biomass but significantly increased plant N content by ≈520 mg (54%). In general, plants grown with 210 and 280 mg·L−1 N during 2005 had the greatest growth (total plant biomass, height), flowering (number of flowers, flower size), and leaf quality (leaf area, chlorophyll content) during forcing in 2006. Urea sprays before defoliation increased plant growth, flowering, and leaf quality characteristics during forcing in 2006. Providing plants with N during the forcing period also increased plant growth, flowering, and leaf quality characteristics. Urea sprays in the fall were as effective as N fertilizer in the spring on improving growth and flowering. We conclude that both vegetative growth and flowering during forcing of ‘Merritt's Supreme’ hydrangea are influenced by both the N status before forcing and N supply from fertilizer during forcing. A combination of optimum rates of N fertigation during the vegetative stage of production with urea sprays before defoliation could be a useful management strategy to control excessive vegetative growth, increase N storage, reduce the total N input, and optimize growth and flowering of container-grown florists’ hydrangeas.

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Carolyn F. Scagel, Richard P. Regan, Rita Hummel, and Guihong Bi

A study was conducted to determine whether nitrogen (N) application rate and fertilizer form are related to cold tolerance of buds and stems using container-grown ‘Summit’ green ash (Fraxinus pennsylvanica) trees. Trees were grown with different rates of N from either urea formaldehyde (UF) or a controlled-release fertilizer (CRF) containing ammonium nitrate during the 2006 growing season; and growth, N and carbon (C) composition, and cold tolerance were evaluated in Oct. 2006, Dec. 2006, and Feb. 2007 by assessing the lowest survival temperature (LST) of stem and bud tissues on current season (2006) stems. Both fertilizer type and rate influenced the bud and stem LSTs. The influence of fertilizer rate was most evident on midwinter (December) stem LSTs and the influence of fertilizer type was observed in bud and stem LSTs during the deacclimation period in February. Higher LSTs were associated with higher N concentrations and lower C/N ratios; however, stems and buds of trees fertilized with UF were more cold-tolerant (had lower LSTs) than stems and buds on trees fertilized with CRF. Fertilizer type resulted in several differences in N and C translocation and metabolism during the fall and winter. Our results indicate trees with a similar N status are able to withstand different levels of cold depending on the rate of N and the type or form of fertilizer used during production. This may have to do with differences in how trees metabolize the different fertilizer forms, where and when the N is stored, and how it is remobilized in the spring, especially in relation to C metabolism.

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Tongyin Li, Guihong Bi, Richard L. Harkess, and Eugene K. Blythe

Mineral nutrient uptake of Encore® azalea ‘Chiffon’ (Rhododendron sp.) affected by nitrogen (N) rate, container type, and irrigation frequency was investigated. One-year-old azalea plants were planted in two types of 1-gallon containers: a black plastic container or a biodegradable container (also referred to as a biocontainer) made from recycled paper. Azalea plants were fertilized with 250 mL of N-free fertilizer twice weekly plus N rates of 0, 5, 10, 15, or 20 mm from ammonium nitrate (NH4NO3). All plants were irrigated daily with the same amount of water through one or two irrigations. Plants fertilized without N had the lowest concentrations of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) averaged in the entire plant, which were at deficient levels for azalea species. High N rates of 15 or 20 mm resulted in the highest plant average concentrations of P, K, Ca, and Mg. Concentrations of micronutrients including iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), and boron (B) showed varied trends affected by different treatments. With high N rates of 15 and 20 mm, paper biocontainers increased uptake of both macro- and micronutrients in terms of total nutrient content (mg or μg per plant) compared with plastic containers. One irrigation per day increased root concentrations of Cu and Zn and root contents of Fe, Zn, Cu, and B, but decreased leaf K concentration compared with two irrigations per day. The beneficial effects of high N rates and biocontainers on mineral nutrient uptake of Encore® azalea ‘Chiffon’ likely indirectly occurred through increasing plant growth.

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Keri L. Paridon, Norman Winter, William B. Evans, and Guihong Bi

Landscape trials were conducted to evaluate 235 cultivars within 66 species in central Mississippi. All entries were grown from seed or vegetatively propagated material. Raised landscape beds were prepared using accepted regional methods. Planting into beds began on 4 April and was completed on 20 April. Plants were given an overall rating based on insect resistance, disease resistance, vigor, flowering, and foliage color. Each cultivar was rated bimonthly until early August when pruning or termination was necessary, depending on each cultivar, at which time rating frequency became once a month through the first freeze. The rating range was 0 to 5, where 5 is optimum and 0 is death. Height (cm) was measured for each cultivar at the same intervals as performance ratings. Heights were recorded to show the average height of each cultivar. No herbicides were applied; handweeding controlled weeds. No insecticides were applied to plants with the exception of the hibiscus where there was severe pressure from sawfly larva. In 2005 central Mississippi experienced a very hot and dry summer. Strong winds and heavy rains in late August and early September associated with Hurricanes Katrina and Rita took their toll on the trial, especially many of the taller cultivars. The top performing cultivars for 2005 were `Intensia Lilac Rose' phlox (Phlox ×), Proven Winners; `Intensia Neon Pink' phlox (Phlox ×), Proven Winners; `Elliottii Wind Dancer' grass (Eragrostis curvula), Pan American Seed; `Intensia Lavender Glow' phlox (Phlox ×), Proven Winners; `Dolce Licorice' heuchera (Heuchera ×), Proven Winners; `Diamond Frost' euphorbia (Euphorbia ×), Proven Winners; `Gold Flake' mecardonia (Mecardonia ×), Proven Winners; `Titan Polka Dot' annual vinca (Catharanthus roseus), Ball Seed; `Sun Fan' scaevola (Scaevola aemula), Proven Winners; `Golden Delicious' salvia (Salvia elegans), Proven Winners.

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Guihong Bi*, Carolyn Scagel, Lailiang Cheng, and Leslie Fuchigami

June-budded `Nonpareil/Nemaguard' almond (Prunus dulcis (Mill) D.A. Webb) trees were fertigated with one of five nitrogen (N) concentrations (0, 5, 10, 15, or 20 mm) in a modified Hoagland's solution from July to September. In October, the trees were sprayed twice with either water or 3% urea, then harvested after natural leaf fall and stored at 2°C. Trees were destructively sampled during winter storage to determine their concentrations of amino acids, protein, and non-structural carbohydrates (TNC). Increasing N supply either via N fertigation during the growing season or with foliar urea applications in the fall increased the concentrations of both free and total amino acids, whereas decreased their C/N ratios. Moreover, as the N supply increased, the proportion of nitrogen stored as free amino acids also increased. However, protein was still the main form of N used for storage. The predominant amino acid in both the free and total amino-acid pools was arginine. Arginin N accounted for an increasing proportion of the total N in both the free and total amino acids as the N supply was increased. However, the proportion of arginine N was higher in the free amino acids than in the total amino acids. A negative relationship was found between total amino acid and non-structural carbohydrate concentrations, suggesting that TNC is increasingly used for N assimilation as the supply of N increases. Urea applications decreased the concentrations of glucose, fructose, and sucrose, but had little influence on concentrations of sorbitol and starch. We conclude that protein is the primary form of storage N, and that arginine is the predominant amino acid. Furthermore, the synthesis of amino acids and proteins comes at the expense of non-structural carbohydrates.

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Guihong Bi, Williams B. Evans, and Glenn B. Fain

Pulp mill ash was evaluated as a substrate component in the production of greenhouse-grown French marigold (Tagetes patula L. ‘Janie Deep Orange’). Peat-based substrates (75:10:15 by volume blend of peatmoss, vermiculite, and perlite) amended with 0% to 50% (by volume) pulp mill ash were compared with a standard commercially available substrate. With the exception of an unfertilized control, each substrate blend contained 5.93 kg·m−3 14N–6.2P–11.6K (3- to 4-month release) and 0.89 kg·m−3 Micromax. Substrates containing higher volumes of ash had finer particles, less air space, and more waterholding capacity than the commercial substrate. Bulk density increased with increasing ash volume, and substrate containing 50% ash had 120% greater bulk density than the commercial substrate. Substrates containing ash generally had higher pH and electrical conductivity (EC) than the commercial substrate with substrate pH and EC increasing with increasing ash volume. In general, marigold plants grown in peat-based substrates with the addition of 0% to 50% ash had similar growth indices, flower dry weights, numbers of flowers, and SPAD values as plants grown in commercial substrate; however, plants grown in substrates containing 30% to 50% ash had lower shoot dry weights or root quality ratings than plants grown in commercial substrate. Plant growth index, shoot dry weight, and root quality rating decreased with increasing ash volume.

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Shufu Dong, Lailiang Cheng, Guihong Bi, and Leslie H. Fuchigami

`Gala'/M26 apple and `Bartlett'/OH97 pear trees growing in containers were treated with either 0, 1, 5, 10, 20, or 30g of urea dissolved in 150 mL of distilled water on 7 Sept. 1999. Two weeks after application, a soil sample from each container was analyzed for NH4 + and NO3 . One day after treatment, the leaves of the apple trees treated with either 20 or 30 g urea wilted and curled and none of the other apple treatments were affected. However, 20 days later, new lateral and terminal buds broke to grow from these two treatments. In contrast, the pear trees showed signs of wilting and leaf necrosis in the 5, 10, 20, and 30 g urea treatments about 6 days after application. Twenty days after treatment, the leaves from the two highest treatments were completely necrotic and remained attached to the trees, while the leaves of 5- and 10-g treatments were partially necrotic and began defoliating. None of the pear trees produced any new lateral or terminal growth. Soil test showed that NH4 + contents of the soils were 54.9, 104.2, 356.9, 884.28, 1154.9, and 1225.2 mg/kg for `Bartlett'/OH97, and 30.2, 62.9, 359.0, 235.1, 529.9, and 499.0 mg/kg for `Gala'/M26 and NO3 contents of the soils were 40.5, 62.4, 211.0, 129.8, 54.5, and 39.5 mg/kg for `Bartlett'/OH97, and 37.6, 42.0, 178.7, 138.2, 186.2, and 142.1 mg/kg for `Gala'/M26 treated with 0, 1, 5, 10, 20, and 30 g urea, respectively.

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Xiaojie Zhao, Guihong Bi, Richard L. Harkess, and Eugene K. Blythe

The form of nitrogen (N) in fertilizer can influence plant growth, nutrient uptake, and physiological processes in the plant. However, few studies have been conducted on the effects of N form on tall bearded (TB) iris (Iris germanica L.). In this study, five NH4:NO3 ratios (0:100, 25:75, 50:50, 75:25, and 100:0) were applied to investigate the response of TB iris to different N form ratios. NH4:NO3 ratios in fertilizer did not affect the leaf, root, and rhizome dry weight, or total plant dry weight. Plant height and SPAD reading were affected by NH4:NO3 ratios in some months, but not over the whole growing season. Neither spring nor fall flowering was influenced by NH4:NO3 ratios. Across the whole growing season, leachate pH was increased by higher NH4:NO3 ratios. At the end of the growing season, concentrations of phosphorous (P), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) in leaf; calcium (Ca), magnesium (Mg), Mn, boron (B) in root; and N, P, Mg, Fe, Mn, and Zn in rhizome tissues were affected by NH4:NO3 ratios. Greater NH4:NO3 ratios increased the uptake of Fe, Mn, and Zn. The net uptake of N was unaffected by NH4:NO3 ratios, which indicates TB iris may not have a preference for either ammonium or nitrate N.

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Youping Sun, Guihong Bi, Genhua Niu, and Christina Perez

The goal of this experiment was to evaluate the efficiency of foliar application of dikegulac sodium on increasing the lateral branching of ‘Merritt’s Supreme’ bigleaf hydrangea (Hydrangea macrophylla). Plants were grown in greenhouses at two locations including El Paso, TX and Kosciusko, MS. Two weeks before application of dikegulac sodium, half of plants were hand-pinched leaving two nodes. Foliar spray of dikegulac sodium at 400, 800, or 1600 mg·L−1 was then applied to pinched and unpinched plants. There were two additional control treatments: pinched or unpinched without application of dikegulac sodium. Data were collected at 2 weeks, 6 weeks, 80 days, and 10 months after treatments. Bigleaf hydrangea plants exhibited severe phytotoxicity including interveinal chlorosis or bleaching of new growth at 2 weeks after application of dikegulac sodium with more pronounced symptoms at higher dikegulac sodium concentrations. The severity of phytotoxicity symptoms became less significant at 6 weeks after treatment. The effect of dikegulac sodium on bigleaf hydrangea plant growth, number of branches, and number of flowers depended on both locations and dosages. In El Paso, TX, dikegulac sodium at 800 or 1600 mg·L−1 inhibited bigleaf hydrangea plant growth at 6 weeks and 80 days after treatment, and this effect disappeared at 10 months after treatment. Dikegulac sodium at all tested dosages doubled or tripled the number of branches of pinched or unpinched bigleaf hydrangea, respectively, at 80 days after treatment. At 10 months after treatment, the number of branches and flowers of bigleaf hydrangea plants tended to increase, but was insignificant. In Kosciusko, MS, dikegulac sodium at 1600 mg·L−1 reduced the plant growth at 6 weeks after treatment. This treatment increased the number of branches and flowers of unpinched plants by 196% and 95% and pinched plants by 53% and 31%, respectively, at 10 months after treatment. Dikegulac sodium application could be used to increase number of branches and flowers and produce compact ‘Merritt’s Supreme’ bigleaf hydrangea. However, the efficacy varied with environmental conditions.