Substrate Drench Research Articles

Paclobutrazol Residues in Recirculated Water in Commercial Greenhouses

Reusing irrigation water has technical, environmental, and financial benefits. However, risks are also associated with the accumulation of agrochemicals, in addition to ions, plant and food safety pathogens, and biofilm organisms. In this project, we measured the concentration of paclobutrazol (a persistent and widely used plant growth regulator) in recirculated water in greenhouses producing ornamental plants in containers. Solutions were collected from catchment tanks at nine commercial greenhouses across seven states in the United States in Spring and Fall 2014. Paclobutrazol was detected in all samples, with differences observed by season, greenhouse operation, paclobutrazol application method, and irrigation method. Across operations, the residual concentration of paclobutrazol was higher in spring for most greenhouses (ranging from 0 to 1100 µg·L−1) compared with the fall (ranging from 0 to 8 µg·L−1). The spray-drench application method resulted in the highest residual concentrations (up to 35 µg·L−1), followed by substrate drench (up to 26 µg·L−1) and foliage spray (concentrations under 3 µg·L−1). Residual concentrations were higher with overhead irrigation (up to 35 µg·L−1) compared with subirrigation systems (up to 15 µg·L−1). Our results indicate that paclobutrazol is likely to be a growth retardant risk in greenhouse operations recirculating water. A clear understanding of the risks associated with recirculated water intends to support the development and implementation of risk management strategies to ensure and promote safe use of recirculated water in greenhouses. Overall, the most effective preventative strategy is to ensure the use of the minimum amount of the a.i. necessary per unit of space and time.

Paclobutrazol Substrate Drenches Control Growth of Nine Black-eyed Susan Cultivars

Our objective was to quantify the efficacy of paclobutrazol substrate drenches on growth of nine black-eyed Susan (Rudbeckia hirta) cultivars. Liners of ‘Autumn Colors’, ‘Cherokee Sunset’, ‘Cherry Brandy’, ‘Denver Daisy’, ‘Glowing’, ‘Happy’, ‘Indian Summer’, ‘Prairie Sun’, and ‘Sunny’ black-eyed Susan were transplanted into 6.5-inch-diameter plastic containers (2 qt) filled with a commercial soilless peat-based substrate. After 16 days, six single-plant replicates received a substrate drench of 5-fl-oz aliquots of solutions containing deionized water [0 mg·L−1 paclobutrazol (control)] or 2.5, 5, 10, or 20 mg·L−1 paclobutrazol (0, 0.375, 0.75, 1.5, and 3.0 mg/pot). Paclobutrazol drenches of 2.5 to 20 mg·L−1 significantly influenced plant height, plant diameter, growth index (GI), and shoot dry weight (SDW) of all black-eyed Susan cultivars, although the magnitude of response to paclobutrazol substrate drench concentration varied with cultivar. For most cultivars, GI, an integrated measurement of height and diameter, was suppressed as paclobutrazol substrate drench concentrations increased from 2.5 to 20 mg·L−1, resulting in plants that were 30% to 43% smaller than untreated plants. Increasing paclobutrazol substrate drench concentrations from 2.5 to 20 mg·L−1 limited SDW of each cultivar differently, although plants were 5% to 59% smaller at 20 mg·L−1 paclobutrazol than untreated plants. Time to flower for ‘Autumn Colors’, ‘Cherry Brandy’, ‘Happy’, ‘Indian Summer’, and ‘Prairie Sunset’ was unaffected by any paclobutrazol substrate drench concentration; however, concentrations of ≤10 mg·L−1 paclobutrazol are suggested for ‘Cherokee Sunset’, ‘Denver Daisy’, ‘Glowing’, and ‘Sunny’, as higher concentrations delay flowering. Our results indicate that growers can attain growth control with substrate drenches containing 5 to 10 mg·L−1 paclobutrazol during greenhouse black-eyed Susan production without delaying flowering.

Foliar Silicon Spray to Strawberry Plants During Summer Cutting Propagation Enhances Resistance of Transplants to High Temperature Stresses

Silicon (Si) has been reported to benefit plant growth and stress resistance. This work aimed to find out an optimal method of Si application to enhance the resistance of strawberry (Fragaria × ananassa Duch.) transplants to high temperatures, commonly experienced in the summer when strawberries are propagated for greenhouse production in Korea. Plants of strawberry “Sulhyang”, “Maehyang”, and “Kuemsil” were subjected to one of five treatments before the cutting propagation: no treatment (control), substrate dressing of a water-soluble silicate fertilizer, substrate drench of 75 mg·L−1 Si (from potassium silicate) to the mother plants, or foliar spray of 75 mg·L−1 Si to either the mother plants or daughter plants. Half of the daughter plants in each Si treatment received continued application of Si through either substrate dressing of a water-soluble silicate fertilizer, substrate drench, or foliar spray after the cutting propagation. A high temperature (43°C) resistance test was conducted in plant growth chambers for 7 days with a 16-h photoperiod with a light intensity of 300 mmol·m−2·s−1 PPFD. During the high temperature test, the rate of decline in the photosynthesis was lower in plants treated with Si than in the control. After the high temperature test, it was observed that Si application significantly increased the shoot fresh weight of transplants. Moreover, the contents of sugars, proteins, and enzymatic (CAT, SOD, POD, and APX) and non-enzymatic (anthocyanin and proline) antioxidants were higher in plants treated with Si throughout the entire propagation period, compared to the control and plants only treated with Si before or after the cutting propagation. Overall, the Si application improved the growth of the transplants regardless of the application method used. Moreover, spraying the daughter plants with Si, and continually spraying the transplants were found to be the best and is recommended to increase the resistance of strawberries to high temperatures during propagation.

Supplemental Nickel Corrects Mouse Ear Disorder of Bitternut Hickory

Abstract While sought after for use in managed landscapes, bitternut hickory [Carya cordiformis (Wang.) K. Koch] remains underutilized in horticulture due its reputation for difficulty with production and transplanting. After learning of issues experienced by growers and observing deformed leaf development of container-grown stock, we examined effects of supplemental nickel applications on seedlings of bitternut hickory. We hypothesized that, like the closely related species pecan [Carya illinoinensis (Wang.) K. Koch], bitternut hickory would be similarly limited in production by a susceptibility to mouse ear disorder as a function of nickel deficiency. Seedlings cultivated with a soilless substrate in 3.8L (#1) nursery pots were treated with either a substrate drench or foliar spray of Nickel Plus® two weeks after budbreak. After 30 days, plants treated with a drench or foliar spray exhibited increased leaf area and decreased number of leaves per unit shoot extension and leaf greenness compared to nontreated controls. Foliar treatments resulted in an 83.5% increase in shoot extension over nontreated controls. Whereas seedlings provided supplemental nickel displayed healthy foliage after treatment, nontreated seedlings exhibited traditional symptoms of mouse ear disorder. These data indicate bitternut hickory is susceptible to mouse ear disorder, an issue remedied by supplementing nickel. Index words: foliar spray, substrate drench, soilless substrate, nursery production, ornamental plants. Chemicals used in this study: nickel lignosulfonate (Nickel Plus®). Species used in this study: bitternut hickory, Carya cordiformis (Wang.) K. Koch

Efficacy of Selected Insecticides as Replacement for Neonicotinoids in Managing Sweetpotato Whitefly on Poinsettia

Management of sweetpotato whitefly (Bemisia tabaci), one of the most economically important pests of poinsettia (Euphorbia pulcherrima), relies heavily on neonicotinoid insecticides. Growers are seeking insecticide alternatives to neonicotinoids due to market demands. Although several systemic and translaminar insecticides have been suggested as alternatives to neonicotinoids, no published study has simultaneously compared their efficacies against sweetpotato whiteflies. This study compared the efficacies of 10 systemic and translaminar alternative insecticides with those of two systemic neonicotinoids, when all products were applied as foliar spray (twice at 14 d) or substrate drench (once) against sweetpotato whiteflies on poinsettia plants. Sweetpotato whitefly nymph and adult densities were examined 2 weeks before the first application (pretreatment), and weekly after the application for 8 weeks. Results showed that insecticides varied greatly in their efficacy, particularly against adults, and that spray application provided more effective suppression of nymphs than drench application. Spray and drench applications of imidacloprid and dinotefuran were consistently the most effective against sweetpotato whitefly nymphs and adults. Among the neonicotinoid alternatives, cyantraniliprole was the most effective insecticide in reducing sweetpotato whitefly nymph densities by both spray and drench application methods, with efficacy comparable to those of imidacloprid and dinotefuran. Although less effective than cyantraniliprole, foliar sprays of afidopyropen, chloratraniliprole, cyclaniliprole, flonicamid, flupyradifurone, pyrifluquinazon, spirotetramat, and sulfoxaflor + spinetoram were also effective against nymphs and could serve as partners in an insecticide rotation program.

Silicon Foliar Spray and Substrate Drench Effects on Plant Growth, Morphology, and Resistance to Wilting with Container-Grown Edible Species

The objective of this study was to evaluate silicon (Si) foliar spray and substrate drench effects on plant growth and morphology for container-grown edible crops during greenhouse production, as well as resistance to plant wilting during post-production. In the first greenhouse experiment, basil received Si foliar sprays at 0, 50, 100, 200, and 400 mg∙L–1 Si. In the second greenhouse experiment, Si was applied as either a foliar spray (500 mg∙L–1 Si) or substrate drench (100 mg∙L–1 Si) with six edible crop species. Supplemental Si increased shoot Si levels but had minimal effects on plant growth and morphology, except for parsley, which resulted in distorted growth and phytotoxicity. In the first experiment, 200 and 400 mg∙L–1 Si foliar sprays increased plant resistance to wilt by 2.2 and 2.5 d, respectively; however, this was not observed in the second experiment. All species accumulated Si with the control (no Si) treatments, indicating trace amounts of Si were taken up from the substrate, fertilizer, spray surfactant, and irrigation water. Only cucumber was classified as a Si “accumulator” with a high capacity for Si uptake. Results emphasize the need to conduct preliminary trials with supplemental Si to avoid issues of phytotoxicity.

Substrate Drench Applications of Flurprimidol and Paclobutrazol Influence Growth of Swamp Sunflower

Swamp sunflower (Helianthus simulans) is an underused perennial plant native to the southeastern United States that produces an abundance of golden yellow inflorescences in the fall. It is a vigorous grower and tolerates a wide variety of soil conditions, growing in wetland and nonwetland habitats. Swamp sunflower warrants wider use in perennial beds and landscapes, and research on production practices to make plants more suitable for shipping could promote its production. This study evaluated the effects of plant growth regulators (PGRs) on the growth and floral attributes of the swamp sunflower. Treatments were applied to rooted cuttings in 1-gal pots as a substrate drench of 1, 2, 4, or 6 mg/pot paclobutrazol; 0.5, 1, 2, or 4 mg/pot flurprimidol; or water (control)/pot for Expt. 1. A second experiment (Expt. 2) applied 4, 6, or 8 mg/pot paclobutrazol; 2, 4, or 6 mg/pot flurprimidol; or water (control)/pot. Six weeks after treatment (WAT) for Expt. 1, paclobutrazol applied at 4 and 6 mg/pot and flurprimidol at 2 and 4 mg/pot resulted in smaller plants (as reflected by growth index) by 29%, 34%, 22%, and 48%, respectively, compared with the control. Furthermore, at the termination (6 WAT) of Expt. 1, the highest rate of flurprimidol produced the smallest plants, with the exception of the highest rate of paclobutrazol. By 6 WAT, plants treated with the highest rate of paclobutrazol and flurprimidol had lower dry weights and higher chlorophyll measurements than control. All PGR treatments for Expt. 2 resulted in smaller plants than the control by 27% to 36% at 4 WAT and 23% to 41% at 6 WAT. Differences for internode length and flower diameter were observed for Expts. 1 and 2, respectively. Results from these experiments suggest a substrate drench application of 6 mg/pot paclobutrazol or 4 mg/pot flurprimidol can be used for producing smaller plants compared with nontreated plants for swamp sunflower under greenhouse conditions.

A Combined Phenotypic and Metabolomic Approach for Elucidating the Biostimulant Action of a Plant-Derived Protein Hydrolysate on Tomato Grown Under Limited Water Availability.

Plant-derived protein hydrolysates (PHs) are an important category of biostimulants able to increase plant growth and crop yield especially under environmental stress conditions. PHs can be applied as foliar spray or soil drench. Foliar spray is generally applied to achieve a relatively short-term response, whereas soil drench is used when a long-term effect is desired. The aim of the study was to elucidate the biostimulant action of PH application method (foliar spray or substrate drench) on morpho-physiological traits and metabolic profile of tomato grown under limited water availability. An untreated control was also included. A high-throughput image-based phenotyping (HTP) approach was used to non-destructively monitor the crop response under limited water availability (40% of container capacity) in a controlled environment. Moreover, metabolic profile of leaves was determined at the end of the trial. Dry biomass of shoots at the end of the trial was significantly correlated with number of green pixels (R2 = 0.90) and projected shoot area, respectively. Both drench and foliar treatments had a positive impact on the digital biomass compared to control while the photosynthetic performance of the plants was slightly influenced by treatments. Overall drench application under limited water availability more positively influenced biomass accumulation and metabolic profile than foliar application. Significantly higher transpiration use efficiency was observed with PH-drench applications indicating better stomatal conductance. The mass-spectrometry based metabolomic analysis allowed the identification of distinct biochemical signatures in PH-treated plants. Metabolomic changes involved a wide and organized range of biochemical processes that included, among others, phytohormones (notably a decrease in cytokinins and an accumulation of salicylates) and lipids (including membrane lipids, sterols, and terpenes). From a general perspective, treated tomato plants exhibited an improved tolerance to reactive oxygen species (ROS)-mediated oxidative imbalance. Such capability to cope with oxidative stress might have resulted from a coordinated action of signaling compounds (salicylic acid and hydroxycinnamic amides), radical scavengers such as carotenoids and prenyl quinones, as well as a reduced biosynthesis of tetrapyrrole coproporphyrins.

Inoculation of Rhizoglomus irregulare or Trichoderma atroviride differentially modulates metabolite profiling of wheat root exudates

Root exudation patterns are linked to, among other things, plant growth, plant-microbe interaction and the priming effect. In this work, two complementary metabolomic approaches (both liquid and gas chromatography coupled to mass spectrometry) were applied to investigate the modulation of root exudation imposed by two beneficial fungi (substrate treatment of Trichoderma atroviride AT10, substrate application of Rhizoglomus irregulare BEG72 and seed treatment with T. atroviride AT10) on wheat (Triticum aestivum L.). The inoculation with R. irregulare elicited significant increases (by 18%, 39% and 20%) in the shoot, root dry biomass and root-to-shoot ratio compared to untreated plants, whereas inoculation with T. atroviride, as a substrate drench or as a seed coating, exhibited intermediate values for these parameters. The metabolomic approach demonstrated a broad chemical diversity, with more than 2900 compounds annotated in the root exudates. Overall, the Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) supervised modelling highlighted a distinctive modulation of the metabolic profile in the root exudates as a function of both fungal inoculation and means of application. Most of the differences could be ascribed to lipids (sterols and membrane lipids), phenolic compounds and terpenoids, siderophores and chelating acids, derivatives of amino acids and phytohormones, and as such, the interaction between the wheat roots and beneficial fungi resulted in a complex response in terms of root exudates, likely involving a cascade of processes. Nonetheless, the changes imposed by plant-microbe interactions can contribute to the support of the biostimulant effects of both T. atroviride and R. irregulare.

Protein Hydrolysate Stimulates Growth in Tomato Coupled With N-Dependent Gene Expression Involved in N Assimilation.

Plant-derived protein hydrolysates (PHs) have received increased attention in the last decade because of their potential to improve yield, nutritional quality as well as tolerance to abiotic stressors. The current study investigated the effects and the molecular mechanisms of a legume-derived PH under optimal and sub-optimal nitrogen (N) concentrations (112 and 7 mg L−1, respectively) in tomato (Solanum lycopersicum L.). Growth and mineral composition of tomato plants treated with PHs by foliar spray or substrate drench were compared to untreated plants. In addition, the expression was determined of genes encoding ammonium and nitrate transporters and seven enzymes involved in N metabolism: nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase 1 (GS1), glutamine synthetase 2 (GS2), ferredoxin-dependent glutamate synthase (GLT), NADH-dependent glutamate synthase (GLS), and glutamate dehydrogenase (GDH). The root and total plant dry weight, SPAD index and leaf nitrogen content were higher by 21, 17, 7, and 6%, respectively, in plants treated by a substrate drench in comparison to untreated tomato plants, whereas foliar application of PH gave intermediate values. PH-treated plants grown with lower N availability showed reduced expression of NR and NiR as well as of nitrate and ammonium transporter transcripts in both leaf and root tissues in comparison with untreated plants; this was especially pronounced after application of PH by substrate drench. Conversely, the transcript level of an amino acid transporter gene was up-regulated in comparison with untreated plants. At high N regime, the transcript levels of the ammonium and amino acid transporters and also NR, NiR, and GLT were significantly up-regulated in root after PH foliar and substrate drench applications compared with untreated plants. An up-regulation was also observed for GS1, GS2, and GDH transcripts in leaf after substrate drench. These results highlighted the potential benefits of using legume PH in vegetable production systems to increase growth and N-nutritional status of plants.

A Vegetal Biopolymer-Based Biostimulant Promoted Root Growth in Melon While Triggering Brassinosteroids and Stress-Related Compounds.

Plant biostimulants are receiving great interest for boosting root growth during the first phenological stages of vegetable crops. The present study aimed at elucidating the morphological, physiological, and metabolomic changes occurring in greenhouse melon treated with the biopolymer-based biostimulant Quik-link, containing lateral root promoting peptides, and lignosulphonates. The vegetal-based biopolymer was applied at five rates (0, 0.06, 0.12, 0.24, or 0.48 mL plant-1) as substrate drench. The application of biopolymer-based biostimulant at 0.12 and 0.24 mL plant-1 enhanced dry weight of melon leaves and total biomass by 30.5 and 27.7%, respectively, compared to biopolymer applications at 0.06 mL plant-1 and untreated plants. The root dry biomass, total root length, and surface in biostimulant-treated plants were significantly higher at 0.24 mL plant-1 and to a lesser extent at 0.12 and 0.48 mL plant-1, in comparison to 0.06 mL plant-1 and untreated melon plants. A convoluted biochemical response to the biostimulant treatment was highlighted through UHPLC/QTOF-MS metabolomics, in which brassinosteroids and their interaction with other hormones appeared to play a pivotal role. Root metabolic profile was more markedly altered than leaves, following application of the biopolymer-based biostimulant. Brassinosteroids triggered in roots could have been involved in changes of root development observed after biostimulant application. These hormones, once transported to shoots, could have caused an hormonal imbalance. Indeed, the involvement of abscisic acid, cytokinins, and gibberellin related compounds was observed in leaves following root application of the biopolymer-based biostimulant. Nonetheless, the treatment triggered an accumulation of several metabolites involved in defense mechanisms against biotic and abiotic stresses, such as flavonoids, carotenoids, and glucosinolates, thus potentially improving resistance toward plant stresses.

Concentration and Timing of Ethephon Drench Applications Interact to Affect Growth and Flowering of Containerized Angelonia and Geranium

Ethephon drenches have been reported to effectively control growth of containerized bedding plants. However, previous researchers have indicated that the effects of ethephon drenches on growth and flowering may differ depending on the timing of applications. Our objectives were to quantify the effects of ethephon concentration, timing of substrate drench application, and their interaction on the growth, size, and flowering of two annual bedding plants. Angelonia (Angelonia angustifolia) and geranium (Pelargonium ×hortorum), seedlings were planted in 10.2-cm-diameter containers filled with a commercial, soilless growing substrate composed of (by vol.) 75% sphagnum peatmoss, and 25% perlite. Five, 10, 15, or 20 days after transplanting seedlings, 70-mL aliquots containing 0, 50, 100, or 200 mg·L−1 ethephon were applied as substrate drenches. Species varied in their growth and flowering responses to ethephon concentration, drench application timing, and their interaction. For angelonia, flowering was delayed most with early applications and high concentrations, and delay was diminished with later applications. Angelonia height was unaffected by late applications, though lateral growth was suppressed 20 days after transplant with 200 mg·L−1 ethephon. Flowering of geranium was only delayed when ethephon was applied 5 days after transplanting, whereas flowering, vegetative height, and shoot dry weight were affected more by earlier applications and higher concentrations. Width and root weight were only affected by ethephon concentration, with growth suppression increasing as concentrations increased. Ethephon is an effective growth regulator when applied as a substrate drench. However, the degree of activity and resulting impact on flowering, size, and growth is influenced by the interaction between ethephon concentrations and the timing of drench applications after transplanting.

Effects of Seaweed Extract Application Rate and Method on Post-production Life of Petunia and Tomato Transplants

Seaweed extracts are widely used as plant growth regulators in agriculture and horticulture for improvement of plant growth and development. This study investigated the effects of rockweed (Ascophyllum nodosum) extract application method (foliar spray or substrate drench) and rate on growth and postharvest drought tolerance of petunia (Petunia hybrida) and tomato (Solanum lycopersicum) transplants grown in a commercial peat/perlite substrate. Foliar sprays significantly affected growth of petunia and tomato, but did not improve drought tolerance of petunia and tomato. Whereas, substrate drenches significantly improved drought tolerance of petunia and tomato compared with the control. Shoot fresh weight (FW), shoot dry weight (DW), root index (RI), and chlorophyll index (SPAD) of petunia and tomato increased significantly with increasing concentration of foliar spray rate up to 5 mL·L−1, but did not change significantly with further higher foliar spray rates. Weekly substrate drenches at 20 mL·L−1 significantly decreased FW, DW, RI, and SPAD values of petunia and tomato. In this study, substrate drench at 5–10 mL·L−1 significantly increased flower number of petunia and tomato. The results of this study suggested that substrate drenches at 5–10 mL·L−1 are appropriate for the improvement of postharvest life of petunia and tomato transplants, and that foliar applications can increase plant growth.

Substrate pH Impacts Efficacy of Ethephon Drenches on Growth of Herbaceous Perennials

Ethephon [(2-chloroethyl) phosphonic acid] is widely used as a growth regulator in floricultural crop production, with foliar sprays as the typical application method. Ethephon efficacy is determined by rate of uptake and subsequent ethylene evolution, which can be influenced by a number of factors, including solution pH. This study examines whether an ethephon substrate drench (100 mg⋅L−1 at a volume of 296 mL per 2.8-L container) would allow for plant uptake in two herbaceous perennials, Verbena bonariensis (L.) ‘Lollipop’ and Veronica spicata (L.) ‘Goodness Grows’, as measured by subsequent effects on shoot growth and days to flower. We also investigated substrate pH effects on ethephon drench efficacy by analyzing the shoot responses to ethephon applied at a range of starting substrate pH (4.5 to 7.0) compared with untreated plants grown under the same substrate pH conditions (controls). One or more measurements of shoot growth (height, width, shoot dry weight) were reduced in both taxa treated with ethephon as compared with controls. Veronica plant growth was not influenced by substrate pH in either the control or ethephon-drenched plants. For Verbena plants receiving the ethephon drench, as substrate pH increased, height and width increased. For example, when ethephon was applied at substrate pH 4.5, finished plant height averaged 32.0 cm, compared with 43.5 cm for those plants that received the drench at a substrate pH of 7.0. Increasing substrate pH conditions also influenced the days to flower in Verbena plants. Ethephon-treated plants at a substrate pH of 4.5 required an average of 6.5 days longer to flower than those at a substrate pH of 7.0. In summary, ethephon drench applications can result in significant growth regulation effects, as seen in both Veronica and Verbena. Furthermore, increasing substrate pH can reduce the efficacy of ethephon drench applications.

Culinary herb growth and appearance in response to high salinity and high pH treatments in substrate-based and substrate-free conditions

SummaryLow irradiance during winter glasshouse production in northern Europe induces elongation of stems and petioles in culinary herbs, leading to taller, weaker plants with a lower leaf density and a reduced shelf-life. Growers are interested in using low-cost alternatives to supplementary lighting to maintain plant quality. Plant stress responses have been shown to reduce growth in many species and appear to use an overlapping set of signals, including increased internal pH. This raises the possibility of using high pH or high salinity treatments to modify plant growth. High pH or high salinity foliar spray or substrate drench treatments were applied to two species of culinary herbs, namely coriander (Coriandrum sativum) and flat-leaf parsley (Petroselinum crispum var. neapolitanum) in three substratebased experiments with both species and one hydroponic experiment with parsley. A transient high salinity (240 mM NaCl) substrate drench treatment was effective in reducing petiole lengths by 10 - 20% in both species. The leaf area and colour of the plants remained unaffected. A high pH foliar spray treatment (20 mM KHCO3, pH 12) had a limited effect on petiole elongation. In parsley grown in a hydroponic system, high salinity (240 mM NaCl) reduced petiole elongation, but did not affect leaf area, colour, electrolyte leakage, or petiole firmness. The deterioration of plant appearance during 14 d storage at 4°C was also reduced by the 240 mM NaCl high salinity treatment. The results indicate that a sub-phytotoxic salinity treatment could provide a low-cost alternative to artificial lighting to control herb growth under commercial conditions.

Paclobutrazol, Uniconazole, or Flurprimidol Applied at Various Concentrations as a Substrate Drench or Through Subirrigation Have Little Effect on Bee Balm Growth

Summer and fall studies investigated the control of growth of bee balm (Monarda didyma ‘Marshall’s Delight’) by paclobutrazol, uniconazole, or flurprimidol applied to the substrate as a surface drench or through subirrigation. Flurprimidol and uniconazole were applied at 0, 0.5, 1.0, 1.5, or 2.0 ppm (0, 0.09, 0.18, 0.27, or 2.0 mg/pot), while paclobutrazol was applied at 0, 2, 4, 6, or 8 ppm (0, 0.6, 1.2, 1.8, or 2.4 mg/pot). Substrate drench applications were more effective than applications through subirrigation at reducing plant growth. Few trends in application concentrations within plant growth regulator occurred for the plant parameters measured. Based on inconsistent plant responses between the two studies and few differences among application concentrations, we do not recommend any of these plant growth regulators for controlling plant size of bee balm during production without further testing in production environments specific to bee balm.

Ethephon Substrate Drenches Inhibit Stem Extension of Floriculture Crops

Ethephon [(2-chloroethyl) phosphonic acid] is a plant growth regulator that releases ethylene on application and can abort flowers, stimulate branching, and inhibit stem elongation. Although ethephon is used as a foliar spray during the commercial production of many ornamental crops, its effectiveness as a drench has not been widely investigated. We performed experiments to quantify the effects of an ethephon drench on growth and flowering of a range of bedding plant and Narcissus cultivars and to assess the effect of lime on ethylene release from a peat substrate. A substrate drench of 0, 100, 250, or 500 mg·L−1 ethephon was applied to 12 potted Narcissus cultivars at one location, and up to 200 mg·L−1 was applied to 24 cultivars of bedding plants at three locations. Compared with untreated controls, ethephon generally reduced plant height at flowering and the effect increased with increased concentration. For example, Narcissus treated with a 250 mg·L−1 ethephon drench had stems that were 20% to 40% shorter at the end of flowering than control plants. However, ethephon drenches generally caused a 2- to 3-day flowering delay, and two cultivars had a phytotoxic response. Among the bedding plants studied, a 100-mg·L−1 ethephon drench suppressed plant height at flowering by greater than 30% in Catharanthus, Celosia, Dianthus, and Verbena, but by only 10% to 15% in Lobelia, Lycopersicon, and Tagetes. The drenches also delayed flowering in 10 of the 16 crops measured and decreased dry mass accumulation in all of the crops measured. Ethephon release from peat substrate became maximal ≈120 h after application and was dramatically increased by incorporation of dolomitic lime up to a rate of 9.5 kg lime per m3 of peat. Collectively, these studies show that ethephon substrate drenches inhibit stem elongation in a broad range of floriculture crops, but can also delay flowering and reduce biomass accumulation.

Height Control of ‘Hot Lips’ Hybrid Sage to Flurprimidol Substrate Drench

Sages (Salvia sp.) have long been popular as summer annuals, culinary herbs, and landscape perennials. We selected ‘Hot Lips’ hybrid sage [Salvia ×microphylla (Salvia greggii × S. microphylla)], a recently introduced perennial sage, to assess efficacy of the growth regulator flurprimidol for controlling height. Substrate drenches of flurprimidol at 0, 0.25, 0.50, 1.0, 2, and 4 mg per pot were applied using 240 mL of solution per pot on 17 June 2010. Plant height was recorded at treatment, 27 days after treatment (DAT), and 48 DAT. Flurprimidol drench concentrations of 0.25 mg per pot and higher controlled plant height by 20% to 41% 27 DAT and by 26% to 50% 48 DAT. While all treatments at 48 DAT produced a significantly shorter plant, concentrations between 0.25 to 1 mg would provide growers options for controlling plant growth by 26% to 44%. Using concentrations over 1.0 mg did not produce any additional control of height in hybrid sage.

INCIDENCE OF BORON DEFICIENCY IN BEDDING PLANTS CAUSED BY DROUGHT STRESS OR ABSCICIC ACID APPLICATION

Growers have reported boron (B) deficiency in pansy (Viola ×wittrockiana) plug production, specifically in plugs grown in the high heat and humidity conditions of summer. Past studies have reported that soil moisture has an impact on boron availability. To simulate drought conditions, ‘Dynamite Yellow’ pansy plants were grown in a peat-based substrate which was allowed to dry down to 40, 30 or 20% container capacity (CC), 10 or 20 days after sowing (DAS) or on a continual basis. Boron tissue concentration was not affected by any induced drought stress, with the exception of those allowed to dry to 40% CC 20 DAS, which had higher levels of boron than the control. To simulate a physiological response to drought stress, exogenous abscisic acid (ABA) was applied as a substrate drench or foliar spray at concentrations of 150 or 300 mg L-1 to ‘Dynamite Yellow’ pansy plants grown in a peat-based substrate 10 or 20 DAS. All treatments resulted in lower tissue concentrations of B compared to an untreated control. Plants treated 10 DAS with a substrate drench (300 mg L-1) or a foliar spray (150 mg L-1) and plants treated 20 DAS with a foliar spray (150 or 300 mg L-1) of ABA showed a reduction in transpiration. Plants had lower ratios of transpiration/leaf area when ABA was applied as a 300 mg L-1 substrate drench 10 DAS and as foliar spray at both concentrations at either application time. The lower B tissue concentrations coupled with lower transpiration rates were similar to circumstances in greenhouse production of fall pansy crops. Boron deficiency is most common in August when high temperatures and relative humidity cause the plants to transpire less.

Silicon supplements affect floricultural quality traits and elemental nutrient concentrations of greenhouse produced gerbera

In greenhouse production most floricultural crops are cultivated in soilless substrates with limited concentrations of the beneficial element silicon (Si). Inclusion of supplemental silicon in greenhouse production is reported to affect the quality of several herbaceous plants that accumulate Si in their tissue. The goals of this study were to evaluate the effects of different Si sources and concentrations on the floricultural quality traits, the Si accumulation in plant tissues and the leaf tissue concentrations of other elemental nutrients of greenhouse produced gerbera ( Gerbera hybrid L. ‘Acapella’). Potassium silicate (KSiO 3) substrate incorporation or weekly substrate drench, sodium silicate (NaSiO 3) foliar application, and rice husk ash substrate incorporation were used as Si supplements. Gerbera plants supplemented with several Si source and rate combinations, particularly NaSiO 3 foliar sprays, produced thicker flower peduncles, increased flower diameters, increased height, and flowered earlier than non-supplemented controls. Gerbera plants grown in Si-supplemented media all accumulated higher levels of silicon in leaf, peduncle and flower tissues than non-supplemented controls. Leaf concentrations of macronutrients, such as sulfur and potassium, and micronutrients such as, boron, copper, iron, and manganese, were slightly changed among Si-supplemented plants. Foliar sprays of NaSiO 3 at a rate of 150 mg Si L −1 caused stem shortening and flower deformation. However, silicon supplements can improve the floricultural traits of greenhouse grown gerberas, but forms and rates of Si must be optimized.