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Silicon (Si) is a plant beneficial element associated with the mitigation of abiotic and biotic stresses. Most greenhouse-grown ornamentals are considered low Si accumulators based on foliar Si concentration. However, Si accumulates in all tissues, and there is little published data on the distribution of Si in plants. This knowledge may be critical to using Si to mitigate tissue-specific plant stresses, e.g., pathogens. Therefore, we quantified Si accumulation and distribution in petunia (Petunia ×hybrida Hort. Vilm.-Andr. ‘Dreams Pink’), a low Si accumulator, and sunflower (Helianthus annuus L. ‘Pacino Gold’), a high Si accumulator. Plants were grown in a sphagnum peat: perlite substrate amended with 0% (−Si) or 20% (+Si) parboiled rice hulls for 53 (petunia) or 72 days (sunflower). Aboveground dry weight was greater in nonamended petunia (13%) and sunflower (18%), compared with rice hull–amended plants, but days to flower was unaffected. Sunflowers grown in the rice hull–amended substrate had the greatest Si concentration in leaves (10,909 mg·kg−1), whereas roots (895 mg·kg−1), stems (303 mg·kg−1), and flowers (252 mg·kg−1) had lower, but similar Si concentrations. In petunia, Si concentration was greatest in leaves (2036 mg·kg−1), then roots (1237 mg·kg−1), followed by stems (301 mg·kg−1), and flowers (247 mg·kg−1). The addition of rice hulls to the substrate increased Si concentration in sunflower 414% in roots, 512% in flowers, 611% in stems, and 766% in leaves. By contrast, Si concentration in petunia increased only 7% in flowers, 105% in stems, and 115% in leaves, but increased 687% in roots. In rice hull–amended sunflowers, the distribution of Si was 91% in leaves, 3% in stems, 3% in roots, and 3% in flowers, and in petunia, it was 72% in leaves, 17% in stems, 6% in roots, and 5% in flowers.

Gasified rice hull biochar (GRHB) is a byproduct of rice production, where rice hulls are gasified to generate energy for other aspects of rice processing. Other research has shown that GRHB up to 10% (v/v) in a soilless substrate can provide much, but not all, of a potted floriculture crops’ phosphorus and potassium needs. The objective of this research was to determine the effect of higher GRHB rates on floriculture crop nutrition and growth. Two experiments were conducted with GRHB rates ranging from 0% to 30% (v/v) of a soilless peatmoss-based substrate. Geranium (Pelargonium ×hortorum ‘Maverick Red’) and tomato (Solanum lycopersicum ‘Megabite’) were grown in 10-cm diameter pots with amended substrates. Addition of GRHB up to 30% affected the physical properties of the peatmoss-based substrate by increasing container capacity (CC) and decreasing unavailable water (UAW). Summarizing across the two experiments, amending a peatmoss substrate with 15% and 20% GRHB provided sufficient P and K for production of geranium and tomato in soilless substrates over a 5 to 6 week production cycle. However, GRHB did not provide a sufficient source of micronutrients to support acceptable crop growth. Geranium responded negatively to high rates (>10%) with reduced shoot and root growth, while tomato responded positively to higher rates with increased shoot growth. Higher rates of GRHB (>10%) can be recommended for some crops, but not all.

Bowers, J. H., and Locke, J. C. 2004. Effect of formulated plant extracts and oils on population density of Phytophthora nicotianae in soil and control of Phytophthora blight in the greenhouse. Plant Dis. 88:11-16. Formulated plant extracts and oils were investigated for control of diseases caused by Phytophthora spp. Soil infested with chlamydospores of Phytophthora nicotianae was treated by incorporating 1, 5, and 10% aqueous emulsions of formulations containing clove oil, neem oil, pepper extract and mustard oil, cassia extract, synthetic cinnamon oil, or the fungicide metalaxyl. Population densities of P. nicotianae were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P < 0.05) differences among treatment mean values at each assay date. After 1 day, population densities were reduced to below the limit of detection (

Horst, L. E., Locke, J., Krause, C. R., McMahon, R. W., Madden, L. V., and Hoitink, H. A. J. 2005. Suppression of Botrytis blight of begonia by Trichoderma hamatum 382 in peat and compost-amended potting mixes. Plant Dis. 89:1195-1200. Inoculation of an industry standard light sphagnum peat potting mix with Trichoderma hamatum 382 (T382) significantly (P = 0.05) reduced the severity of Botrytis blight, caused by Botrytis cinerea, on begonia plants grown in a greenhouse. In data combined from three experiments, the degree of control provided by T382 did not differ significantly (P = 0.05) from that provided by weekly topical sprays with chlorothalonil. In addition, T382 significantly (P = 0.05) increased shoot dry weight and salability of flowering plants. Incorporation of composted cow manure (5%, vol/vol) into the light peat mix also significantly (P = 0.05) decreased blight severity while shoot dry weight and salability were increased. Blight severity on plants in this compost mix did not differ significantly (P = 0.05) from that on those in the light peat mix inoculated with T382. Finally, T382 and chlorothalonil did not significantly (P = 0.05) affect blight severity, shoot dry weight, or salability of plants grown in the compost mix. Spatial separation was maintained in begonias between the biocontrol agent T382 and the pathogen. It was concluded, therefore, that the decrease in disease severity provided by inoculation of the peat mix with T382 most likely was due to systemic resistance induced in begonia against Botrytis blight. The suppressive effect of the compost mix against Botrytis blight was unusual because composts typically do not provide such effects unless inoculated with a biocontrol agent capable of inducing systemic resistance in plants to disease.

The objective of this research was to determine the suitability of a steel slag product for supplying micronutrients to container-grown floriculture crops. Geranium (Pelargonium ×hortorum L.H. Bailey ‘Maverick Red’) and tomato (Solanum lycopersicon L. ‘Megabite’) were grown in 11.4-cm containers with a substrate composed of 85 peatmoss : 15 perlite (v/v). A group of containers referred to as the commercial control (C-control) were amended with 4.8 kg·m−3 dolomitic lime and fertilized with a commercial complete fertilizer providing macro and micronutrients (Jack’s 20N–4.4P–16.6K–0.15Mg–0.02B–0.01Cu–0.1Fe–0.05Mn–0.01Mo–0.05Zn) at a concentration of 100 mg·L−1 nitrogen (N). Another group of containers, referred to as the micronutrient control (M-control), were amended with a commercial granular micronutrient package at 0.9 kg·m−3 and dolomitic lime at 4.8 kg·m−3. The M-controls were fertilized with 7.1 mm N (100 mg·L−1 N) with ammonium nitrate and 2 mm potassium phosphate. A final group of containers were amended with 1.2, 2.4, or 4.8 kg·m−3 of steel slag and fertilized with 3.6 mm ammonium nitrate and 2 mm potassium phosphate. Both control groups resulted in vigorous and saleable plants by the conclusion of the experiment. In both crops, chlorophyll levels, root ratings, and shoot dry mass were lower in all steel slag–amended plants compared with either control groups. In geranium, foliar nutrient concentrations suggest Cu and Zn were limiting whereas B and Zn were limiting in tomato. Based on the results of this research, steel slag does not provide sufficient micronutrients, most notably B, Cu, and Zn, to be the sole source of micronutrient fertilization in container-grown crops.

Dolomitic lime (DL) is the primary liming agent used for increasing pH in peatmoss-based substrates. Steel slag (SS) is a byproduct of the steel manufacturing industry that has been used to elevate field soil pH. The objective of this research was to determine the pH response of a peatmoss-based greenhouse substrate to varying rates of DL or SS. Two experiments were conducted with an 85 peatmoss : 15 perlite substrate. In the first experiment, the substrate was amended with 0, 2.4, 4.8, or 7.1 kg·m−3 of either DL or SS. Half of the containers remained fallow and the other half were potted with a single sunflower (Helianthus annuus L. ‘Pacino Gold’). In the second experiment, fallow containers were only used with the substrate amended with 0, 2.4, 4.8, 9.5, or 14.2 kg·m−3 DL or SS. Sunflower were measured for relative foliar chlorophyll content, shoot mass, root ratings, and foliar nutrient concentrations. Substrate electrical conductivity (EC) and pH were measured weekly using the pour-through procedure. All sunflower plants grew vigorously, although nonamended controls had less shoot dry weight than those amended with DL or SS. There were minor differences in foliar concentration of N, Ca, Mg, and Mn; however, these differences did not adversely affect plant growth. Summarizing across both experiments, EC was affected by treatment and time, although all substrates had EC readings within the range recommended for floriculture crop production (1.0–4.6 mS⋅cm−1). Substrate pH differed slightly in Expt. 1 between fallow and planted containers. Substrate pH increased exponentially with increasing rates of either DL or SS. Maximum pH in fallow DL and SS amended substrates was 6.57 and 6.93, respectively, in Expt. 1 and 6.85 and 7.67, respectively, in Expt. 2. The SS used in this experiment resulted in a greater pH response than DL with higher application rates. SS is a viable material for raising pH of soilless substrates.

Phosphate fertilizers used in the production of greenhouse crops can be problematic if released into the environment. Furthermore, the price of phosphate is increasing as demand increases and world supplies decrease. The objective of this research was to determine if gasified rice hull biochar (GRHB), inherently high in phosphorus concentration, could be used as an amendment to greenhouse substrates to eliminate the need for phosphorus fertilizer application. Geranium (Pelargonium xhortorum ‘Maverick Red’), pansy (Viola xwittrockiana ‘Mammoth Blue Deep Dazzle’), sunflower (Helianthus annus ‘Pacino Gold’), zinnia (Zinnia elegans ‘Oklahoma White’), and tomato (Lycopersicon esculentum ‘Mega Bite’) were grown in a standard commercial soilless medium composed of 85 : 15 sphagnum peat moss : perlite (v:v) and amended volumetrically with 0, 5, or 10% GRHB (v/v). A group of plants labeled as NPK-fertilized controls were fertilized with 7.1 mM N, 0.7 mM P, and 1.4 mM K derived from ammonium nitrate (NH4NO3) and potassium phosphate (K2HPO4). Other treatments received 0, 5, or 10% GRHB and fertilized with 7.1 mM N using NH4NO3. Gasified rice hull biochar had little effect on substrate pH over the course of the experiment. While pH was higher with 10% GRHB than NPK30 fertilized controls by 6 weeks after potting (WAP), the difference was only 0.19 pH units. The GRHB used in this study is an excellent source of readily available phosphate when incorporated at 5% or 10%. However, P is readily leached from containers and lacking in substrate solution concentration by 4 WAP when containers are irrigated and leached in a manner similar to this experiment. While the five crops grown in this study were of similar size and lacked any signs of nutrient deficiency when amended with GRHB, foliar concentrations of P were low when their only source was from pre-incorporated GRHB. Gasified rice hull biochar has potential to be used as a 36 P source in floriculture crop production, however, leaching of the substrate must be minimized to prevent P loss.

Biochar materials have been reported to improve the chemical, physical, and biological properties of mineral soils and soilless substrates. The objective of this research was to determine the effect of gasified rice hull biochar (GRHB) on available nutrients in a container substrate. Two experiments were conducted in a glasshouse with geranium (Pelargonium xhortorum ‘Maverick Red’) in 10 cm (4 in) pots. Geranium were potted in commercial soilless medium (Sunshine Mix #2) amended with 0 to 10% GRHB. Control pots were fertilized with a commercial complete liquid fertilizer (20N-4.4P-16.6K-0.15Mg-0.02B-0.01Cu-0.1Fe-0.05Mn-0.01Mo-0.05Zn), while GRHB-amended crops were fertilized with ammonium nitrate. Additional GRHB substrates were amended with either 0 or 0.9 kg·m−3 (1.5 lb·yd−3) micronutrient package (Micromax). The GRHB amendment had little or no effect on substrate pH. Amendment with GRHB increased available phosphate and potassium in substrate leachates compared to the commercially fertilized controls. Substrates amended with GRHB alone were chlorotic and grew less than those amended with GRHB and micronutrients. These data demonstrate that GRHB provides sufficient P and K to support a six week production cycle of geranium, but lacks either the correct concentration or balance of micronutrients for healthy growth.

Better management of nutrient applications during a growing season is needed to economically produce marketable container-grown ornamental shade trees. Fertilizer practices were used to test the growth of Acer rubrum ‘Red Sunset’ trees in two commercial nursery fields (each containing four plots) that were irrigated with either city or pond water. In each field, the same 16 treatments were replicated. Two slow-release granular fertilizers (18-5-12 and 12-0-42) were applied separately or together by incorporation, topdress or both to a potting mix for trees grown in 26 liter (7 gal) containers and placed above or below ground. Trees irrigated with pond water also received supplemental liquid nutrients throughout the growing season along with nitric acid to lower the pH of the potting substrate. Tree growth was assessed by stem diameter (caliper), height, canopy size, leaf color and root measurements. Significant higher caliper increases occurred in trees treated with 18-5-12 fertilizer and irrigated with either pond or city water than trees treated with the 12-0-42 fertilizer. Significantly higher percent increases in caliper also occurred for trees irrigated with pond water and top-dressed with 18-5-12 fertilizer than trees with incorporated 18-5-12 fertilizer. With the same slow-release fertilizer applications, trees irrigated with pond water and supplemental nutrients had greater percent increases of caliper, larger canopy areas and better root systems than trees irrigated with city water. The differences in tree height increase were not as great as the caliper increases. However, tree growth irrigated with pond water required additional inputs with extra nutrients and labor costs throughout the growing season.

Wheat (Triticum sp.) straw is being evaluated as a potential component in soilless container mixes either alone or combined with compost to replace a significant portion of the substrate currently supplied by pine bark and peat moss. The objective of this study was to evaluate wheat straw and horse manure compost, locally available resources, as components of container media for establishing and overwintering daylily (Hemerocallis fulva ‘Stella D'Oro’). A standard commercial, sphagnum peat-based substrate was amended with either wheat straw, horse manure compost, or a combination of the two. Stella D'Oro daylily divisions were grown in each substrate mix and overwintered in an unheated structure for eight months. Physical properties of the mixes were determined to be within production standards and media shrinkage was minimal. Daylilies in all substrate combinations were of comparable vigor to the non-amended substrate when growth resumed in the spring.

Pine bark (PB) is the primary component in nursery substrates in the United States. Availability of pine bark is decreasing and price is increasing. The objective of this research was to determine if miscanthus straw (MS) can replace all or part of the pine bark fraction in nursery container substrates. Five substrates were created that contained 15% sphagnum peatmoss, 5% municipal solid waste compost, and the remaining 80% consisted of one of the five following PB:MS ratios: 0:80, 20:60, 40:40, 60:20, and 80:0. Luna Red hibiscus (Hibiscus moscheutos) were grown in each substrate and evaluated for eight weeks in a greenhouse. Ground MS increased air space and decreased container capacity and bulk density as its concentration in the substrate increased. Additions of MS did not affect hibiscus chlorophyll content, and had negligible effects on hibiscus foliar nutrient levels. Increasing levels of MS caused a decrease in plant shoot dry weight, although growth reduction was most pronounced with 80% MS. Ground MS has potential to be a suitable substrate for nursery growers, however, some changes to management practices will be necessary.

Silicon (Si) detection, distribution, and quantification in plants was compared using electron beam analysis (EBA; scanning electron microscopy coupled with energy dispersive X‐ray analysis), colorimetric analysis, and inductively coupled plasma–optical emission spectroscopy (ICP‐OES) in 14 economically important floriculture species. Using EBA, Si was identified most commonly around the base of trichomes and along the leaf margins. The ICP‐OES processing and analysis for Si using sodium hydroxide (NaOH) resulted in damaged torches and microwavable Teflon® vessels that required expensive replacement at the end of each run, but this was not the case in the colorimetric method or with a potassium hydroxide (KOH)–based matrix in the ICP‐OES. The results of these analyses suggest there is agreement between quantification methods, and EBA has a lower detection limit of about 300 mg kg−1 dry weight of Si. Several new floriculture species (zinnia, impatiens, verbena, and calibrachoa) were identified that take up...

Pelargonium was a priority genera collected by the Ornamental Plant Germplasm Center (OPGC) until a recent reorganization. To preserve genetic diversity for future breeders, OPGC collects heirloom cultivars, breeding lines, and wild species. The current Pelargonium collection at OPGC consists primarily of cultivars originating from P. ×hortorum and P. ×domesticum. Target region amplification polymorphism (TRAP) has the advantage of producing a large number of markers through use of sequence information that is already available. Our first goal was to determine the feasibility of TRAP for the analysis of this large collection, so that in the future the most diverse genotypes may be retained. To achieve this goal, we first modified existing DNA extraction techniques to account for the high levels of phenolic compounds present in some Pelargonium species by combining several washes to remove the phenolics with the addition of high levels of antiphenolic compounds. Second, we evaluated the TRAP procedure using the DNA isolated from 46 accessions. For 44 accessions, one or two primer combinations generated enough fragments to discriminate each of the accessions, and similar clades were produced by cluster analysis of the polymorphic fragments amplified by different primer combinations. All the scorable fragments were polymorphic, for one primer combination there were 148 markers from one image and the other produced 160 markers on two images. These results demonstrate that TRAP is an effective method for molecular characterization of ornamental collections.

Unique growing containers and nontraditional types of plant presentation may lead to new production problems for growers. This study was conducted to evaluate the growth of a popular container plant, calibrachoa (Calibrachoa ×hybrida), produced in hanging flower pouches using different growing substrate compositions, polymer amendments, and the layering of substrate types of differing moisture holding capacity with the goal of achieving more uniform plant growth and improved after-sale maintenance. Plastic cylindrical hanging pouches were filled with one of nine hydrated substrate types or combinations. Rooted cuttings of ‘Colorburst Violet’ calibrachoa were planted as indicator plants to identify treatment effects because of their susceptibility to iron deficiency-induced chlorosis of new leaves. Daily measurements of substrate moisture were taken to determine the need for irrigation. Chlorophyll content was estimated nondestructively with a hand-held chlorophyll meter to determine the impact of moisture content. Light, porous substrates resulted in the most uniformly green plants and high numbers of flowers from top to bottom. A layered pouch with heavy, compost-amended substrate above a light, porous layer also produced high-quality, uniform plants. This enabled water to be distributed more uniformly throughout the container volume. This study provides fundamental information on how container geometry and soil moisture retention can influence water management decisions by the grower.

Plant performance and appearance in deficient and toxic levels of nutrients are well characterized. However, less is known about the potential subtleties of plant growth, form, development, nutrient uptake, and biotic stress tolerance in the broad tolerable range. Begonia [Beg (Begonia × tuberhybrida Voss)] and new guinea impatiens [NGI (Impatiens hawkeri Bull.)] were grown over a wide range of N (from 1.78 to 57.1 mm NH4:NO3 ratio at a 1:1 ratio supplied as nutrient solution) in a peat:perlite soilless substrate in greenhouse conditions. Plant growth, development, chlorophyll content, leaf angle, nutrient uptake, tissue caloric value, and susceptibility to Botrytis cinerea Pers.:Fr. disease were evaluated in two experiments. Elevated N supply resulted in decreased plant height (16% in Beg and 7% to 16% in NGI), flower count (3% to 48% in Beg and 7% to 49% in NGI), bud numbers (23% to 80% in Beg), canopy area (11% to 33% in NGI), and mass (21% to 33% in Beg and 18% to 58% in NGI). Chlorophyll content saturated at an N supply of 28.6 mm. N uptake efficiency, shoot N use efficiency, and shoot N utilization efficiency decreased with increasing N supply. Elevated levels of N supply from 7.15 to 57.1 mm also increased the susceptibility of Beg to B. cinerea disease by 10% to 80% in stems and 3% to 14% in leaves. The increase in susceptibility also corresponded with increased tissue energy content (kJ·g−1) and altered leaf orientation. This study indicates many plant changes occur between nutrient extremes that can have a significant impact on growth, development, and the ability to withstand disease.

An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca2+ and Mg2+). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.

Several commercial formulations of botanical extracts and essential oils are being investigated as possible alternatives to soil fumigation for control of Fusarium wilt diseases. Soil infested with Fusarium oxysporum f. sp. chrysanthemi was treated with 1, 5, and 10% aqueous emulsions of formulated extracts of clove (70% clove oil), neem (90% neem oil), pepper/mustard (chili pepper extract and essential oil of mustard), cassia (extract of cassia tree), and Banrot (a standard fungicide applied at different labeled rates) in separate experiments. Population densities of F. oxysporum f. sp. chrysanthemi were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P < 0.05) differences among treatment means at each assay date. After 3 days, pepper/mustard, cassia, and clove extracts added as 10% aqueous emulsions reduced the population density of F. oxysporum f. sp. chrysanthemi 99.9, 96.1, and 97.5%, respectively, compared with the untreated control. Neem oil extract increased the population density of F. oxysporum f. sp. chrysanthemi at all concentrations tested. Banrot did not reduce the population density of F. oxysporum f. sp. chrysanthemi in any experiment. In a second, related experiment, soil infested with Fusarium oxysporum f. sp. melonis also was treated with 1, 5, and 10% aqueous emulsions of formulated extracts, incubated in closed plastic bags for 1 week, and planted with muskmelon seeds (cv. Gold Star) in the greenhouse. Treatment of infested soil with 5 and 10% aqueous emulsions of the botanical extracts resulted in differences among treatments after 5 to 6 weeks. The pepper/mustard, cassia, and clove extracts suppressed disease development in repeated experiments (80 to 100% healthy plant stand) compared with the untreated infested soil (

Studies were conducted to examine the effect of treating Zinnia elegans Jacq. with soluble silicon on the performance of the green peach aphid, Myzus persicae (Sulzer). Z. elegans plants were irrigated every 2 d throughout the duration of the experiment with a nutrient solution amended with potassium silicate (K2SiO2), or a nutrient solution without K2SiO2. Length of the prereproductive period and survivorship of M. persicae were not affected by K2SiO2 treatment, but total cumulative fecundity and the intrinsic rate of increase (r(m)) were slightly reduced on Z. elegans plants receiving soluble silicon. Quantification of silicon content in leaf tissues using inductively coupled plasma optical emission spectroscopy (ICP-OES) confirmed significantly higher silicon concentrations in plants treated with K2SiO2 compared with control plants. High performance liquid chromatography-mass spectrometry (HPLC-MS) analysis was used to identify and quantify phenolic acids and flavonols in leaf tissue of Z. elegans. Compared with untreated control plants, significant elevations in 5-caffeoylquinic acid, p-coumaroylquinic acid, and rutin were detected in leaves of Z. elegans plants treated with K2SiO2, but none of seven other phenolics were significantly affected. Similarly, a slight elevation in guaiacol peroxidase activity was detected in plants treated with K2SiO2 Overall, these results indicate treatment of Z. elegans with soluble silicon provides a modest increase in resistance levels to M. persicae, which may be caused in part by defense-related compounds.

Handgun applications are popular general purpose greenhouse sprayers. However, there are few recommendations on how to use them to treat plant benches. Handgun applications made from one side can also result in significant differences in deposits between the side of the plant facing the spray stream and the opposite side. The objectives of this research were to determine how handgun spraying and broadcast applications using twin-fan sprays and air-assistance affect underleaf spray deposits. A bench-top trial was conducted using a mature poinsettia canopy in a

Tiger grass [Thysanolaena maxima (Roxb.) Kuntze] is a popular ornamental grass grown throughout landscapes in South Florida. In the summer of 2006, a leaf spot was observed on tiger grass in the landscape and a commercial nursery in Homestead, FL. The causal agent of the leaf spot was isolated and characterized morphologically and molecularly as Exserohilum rostratum (Drechsler) Leonard & Suggs. At high inoculum densities, symptoms were apparent as early as 12 h after inoculation, and caused widespread necrosis. Germinating conidia of E. rostratum and appressoria were observed in direct association with lesions. This newly discovered disease could potentially have a dramatic effect on the aesthetic quality and salability of this landscape ornamental. Accepted for publication 24 September 2009. Published 15 December 2009.

Greenhouse pesticide labels lack specific recommendations on the spray volume and spray droplet sizes which will provide the most efficacious pest management. A greenhouse trial was established to determine differences in spray retention in a poinsettia canopy between applications using three different spray volumes and three different spray qualities using single nozzle handgun applicators. For the same areas of the canopy, there were few differences in spray deposit between treatments. Fronts and upper areas of the canopy received more deposits than the backs and lower areas of the canopy. There were no significant differences in recovery of fungicide from leaves between treatments. The high volume application produced the highest deposits on artificial targets across all spray qualities. There were no significant differences in overall spray deposit between the low and medium volume treatments.

Experimentally determined mean pK(a) values of carboxyl residues located at the N-termini of alpha-helices are lower than their overall mean values. Here, we perform three types of analyses to account for this phenomenon. We estimate the magnitude of the helix macrodipole to determine its potential role in lowering carboxyl pK(a) values at the N-termini. No correlation between the magnitude of the macrodipole and the pK(a) values is observed. Using the pK(a) program propKa we compare the molecular surroundings of 18 N-termini carboxyl residues versus 233 protein carboxyl groups from a previously studied database. Although pK(a) lowering interactions at the N-termini are similar in nature to those encountered in other protein regions, pK(a) lowering backbone and side-chain hydrogen bonds appear in greater number at the N-termini. For both Asp and Glu, there are about 0.5 more hydrogen bonds per residue at the N-termini than in other protein regions, which can be used to explain their lower than average pK(a) values. Using a QM-based pK(a) prediction model, we investigate the chemical environment of the two lowest Asp and the two lowest Glu pK(a) values at the N-termini so as to quantify the effect of various pK(a) determinants. We show that local interactions suffice to account for the acidity of carboxyl residues at the N-termini. The effect of the helix dipole on carboxyl pK(a) values, if any, is marginal. Backbone amide hydrogen bonds constitute the single biggest contributor to the lowest carboxyl pK(a) values at the N-termini. Their estimated pK(a) lowering effects range from about 1.0 to 1.9 pK(a) units.

Although silicon (Si) is not considered to be an essential plant nutrient because most plants can complete their life cycle without it, many investigators have shown a positive growth effect, such as increased disease resistance, if Si is present. The effect of Si on many ornamental and greenhouse crop species has not been extensively studied. In greenhouse culture, plants are not exposed to Si from mineral soil, so Si should be added to the fertilizer solutions with mineral soil or soil amendments if there are benefits of Si. The initial step in determining potential benefits of Si requires the documentation of Si uptake and localization within the plant. We grew New Guinea impatiens for four weeks and exposed them to 2.0 mM Si in the form of K2SiO4. Using scanning electron microscopy and energy dispersive X-ray analysis, we detected Si deposits on the leaf margins in unique, Si-filled cells, primarily near hydathodes. We did not detect Si in the xylem. This report is the first documentation of Si uptake or accumulation in any species of the Balsaminaceae family. Accepted for publication 12 January 2005. Published 17 February 2005.

Geranium (Pelargonium ×hortorum) is considered to be one of the top-selling floriculture plants, and is highly responsive to increased macro- and micronutrient bioavailability. In spite of its economic importance, there are few nutrient disorder symptoms reported for this species. The lack of nutritional information contributes to suboptimal geranium production quality. Understanding the bioenergetic construction costs during nutrient deficiency can provide insight into the significance of that element predisposing plants to other stress. Therefore, this study was conducted to investigate the impact of nutrient deficiency on plant growth. Pelargonium plants were grown hydroponically in a glass greenhouse. The treatment consisted of a complete modified Hoagland's millimolar concentrations of macronutrients (15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S) and micromolar concentrations of micronutrients (72 Fe, 9.0 Mn, 1.5 Cu, 1.5 Zn, 45.0 B, and 0.1 Mo) and 10 additional solutions each devoid of one essential nutrient (N, P, Ca, Mg, S, Fe, Mn, Cu, Zn, or B). The plants were photographed and divided into young, maturing, and old leaves, the respective petioles, young and old stems, flowers, buds, and roots at “hidden hunger,” incipient, mid- and advanced-stages of nutrient stress. Unique visual deficiency symptoms of interveinal red pigmentation were noted on the matured leaves of P- and Mg-deficient plants, while N-deficient plants developed chlorotic leaf margins. Tissue N concentration greatly influenced bioenergetic construction costs, probably due to differences in protein content. This information will provide an additional tool in producing premium geraniums for the greenhouse industry.

There are several commercial materials available that have remarkable hydrating properties and many claim them to be ideal for use in horticulture and deliver water to the roots better than other soilless media. These are often referred to as “hydrogels.” There is general agreement in the literature that the physical characteristics of hydrogels are altered in the presence of divalent cations such as Ca and Mg. Tap water can reduce the water holding capacity by 70% or more. Unfortunately, the literature agrees on little else in terms of the performance of hydrogels. Some of the confusion is caused in part by comparing one type of hydrogel to another but treating all as equal. There has been no mathematical performance evaluation of hydrogel and what affect the environment may play in that performance to predict potential irrigation savings or shelf life extension. In a series of greenhouse and laboratory studies, we have evaluated the physical characteristics of several types of hydrogels and characterized bedding plant performance throughout a typical growth cycle. We measured leaf expansion, water content of the media, root growth, flowering, and fresh and dry masses. We have found little to no differences in the rate of leaf expansion when using hydrogels, but enhanced root growth early in production with the hydrogels. Our results indicated that plant growth was enhanced early in production, but any advantage they may have was lost by the end of production. Plants grown in hydrogels needed irrigation less frequently than those without hydrogel, but the effect was diminished over time. Since the use of the material can add about 15% to the cost of potting media, this data is designed to assist growers in hydrogel use and to determine any benefits of the added costs.

The antifungal properties of a hydrophobic neem (Azadirachta indica A. Juss.) seed extract (clarified neem oil) were tested against three postharvest apple (Malus domestica Borkh.) pathogens— Botrytis cinerea (pers.) ex Fr. (gray mold), Penicillium expansum Thom. (blue mold rot), and Glomerella cingulata (Ston.) Spauld. & Schrenk. (bitter rot). The antifungal activity of neem seed oil also was compared to that of CaCl 2. A 2% aqueous emulsion of the clarified neem seed oil was moderately fungicidal to B. cinerea and G. cingulata in inoculated fruit, but bad little activity against P. expansum. Ethylene production was reduced 80% in fruit dipped in 2% neem seed oil compared to wounded, inoculated controls. Neem seed oil was as effective an antifungal agent as CaCl 2, but the effects of the two combined were not additive. Recently, using fungicides to control post- harvest decay of fruit and vegetables has been restricted severely. Many compounds are be- ing removed from use, rather than undergoing the stringent tests required for re-registration. The challenge to reduce postharvest losses by means other than synthetic fungicides led us to investigate the use of a natural material re- ported to have antimicrobial activity (Kher and Chaurasia, 1977; Locke, 1986, 1990).

The repellency and toxicity of a petroleum-based proprietary horticultural oil, Sunspray 6E Plus, was tested against the greenhouse whitefly, Trialeurodes vapor-ariorum (Westwood), on greenhouse-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura cv. Iceberg]. A 2% (v/v) aqueous spray repelled adult whiteflies for at least 11 days after spraying and it was toxic to newly hatched and third stage larval whiteflies. No phytotoxicity was observed when four weekly sprays of 1%, 2%, and 4% oil were applied.