Container-grown Ornamental Plants Research Articles

Ornamental Plant and Weed Response to Oxyfluorfen Plus Prodiamine

Ornamental plant and weed response to oxyfluorfen + prodiamine herbicide was evaluated in Connecticut and Tennessee, USA, in 2017 and 2018. Preemergence application of oxyfluorfen + prodiamine was made at 0 lb/acre, 2 + 0.75 lb/acre, 4 + 1.5 lb/acre, and 8 + 3 lb/acre to container-grown ornamental plants on an outdoor gravel pad and weeds in greenhouse experiments. Ornamental plants were treated first within a week after transplanting and again 6 weeks after the first treatment. Asiatic jasmine (Trachelospermum asiaticum), candlestick plant (Senna alata), and English ivy (Hedera helix) in Tennessee, USA; and ‘Blue Flag’ iris (Iris sp.), ‘Firecracker’ gladiolus (Gladiolus sp.), and ‘Green Carpet’ Japanese pachysandra (Pachysandra terminalis) in Connecticut, USA, were not injured with oxyfluorfen + prodiamine regardless of rate applied. Lily-of-the-Nile (Agapanthus africanus) in Tennessee, USA, and ‘Bowles’ periwinkle (Vinca minor) in Connecticut, USA, showed minor but commercially acceptable growth reduction with oxyfluorfen + prodiamine up to 4 + 1.5 lb/acre. Shasta daisy (Leucanthemum ×superbum) in Connecticut, USA, was the most sensitive ornamental plant. After the first application, average necrotic injury to Shasta daisy varied from 24% with 2 + 0.75 lb/acre to 31% with 8 + 3 lb/acre of oxyfluorfen + prodiamine. After the second application, necrotic injury was ≤ 5% with all oxyfluorfen + prodiamine rates tested and was commercially acceptable (≤ 20%). Oxyfluorfen + prodiamine reduced densities of creeping woodsorrel (Oxalis corniculata), hairy bittercress (Cardamine hirsuta), giant foxtail (Setaria faberi), and large crabgrass (Digitaria sanguinalis) ≥ 80% by 4 weeks after treatment. The fresh weed biomass 6 weeks after treatment indicated an 88% to 99% reduction compared with the untreated control.

Nutrient availability and plant phenological stage influence the substrate microbiome in container-grown Impatiens walleriana ‘Xtreme Red’

BackgroundThe microbiome plays a fundamental role in plant health and performance. Soil serves as a reservoir of microbial diversity where plants attract microorganisms via root exudates. The soil has an important impact on the composition of the rhizosphere microbiome, but greenhouse ornamental plants are commonly grown in soilless substrates. While soil microbiomes have been extensively studied in traditional agriculture to improve plant performance, health, and sustainability, information about the microbiomes of soilless substrates is still limited. Thus, we conducted an experiment to explore the microbiome of a peat-based substrate used in container production of Impatiens walleriana, a popular greenhouse ornamental plant. We investigated the effects of plant phenological stage and fertilization level on the substrate microbiome.ResultsImpatiens plants grown under low fertilization rates were smaller and produced more flowers than plants grown under optimum and high fertilization. The top five bacterial phyla present in the substrate were Proteobacteria, Actinobacteria, Bacteriodota, Verrucomicrobiota, and Planctomycetota. We found a total of 2,535 amplicon sequence variants (ASV) grouped into 299 genera. The substrate core microbiome was represented by only 1.8% (48) of the identified ASV. The microbiome community composition was influenced by plant phenological stage and fertilizer levels. Phenological stage exhibited a stronger influence on microbiome composition than fertilizer levels. Differential abundance analysis using DESeq2 identified more ASVs significantly affected (enriched or depleted) in the high fertilizer levels at flowering. As observed for community composition, the effect of plant phenological stage on microbial community function was stronger than fertilizer level. Phenological stage and fertilizer treatments did not affect alpha-diversity in the substrate.ConclusionsIn container-grown ornamental plants, the substrate serves as the main microbial reservoir for the plant, and the plant and agricultural inputs (fertilization) modulate the microbial community structure and function of the substrate. The differences observed in substrate microbiome composition across plant phenological stage were explained by pH, total organic carbon (TOC) and fluoride, and across fertilizer levels by pH and phosphate (PO4). Our project provides an initial diversity profile of the bacteria occurring in soilless substrates, an underexplored source of microbial diversity.

Weed Control Efficacy and Ornamental Plant Tolerance to Dimethenamid–p + Pendimethalin Granular Herbicide

Abstract Weed control efficacy and ornamental plants tolerance to dimethenamid–p (0.75%) + pendimethalin (1%) granular herbicide was evaluated in flat tray-grown weeds and container-grown ornamental plants. Dimethenamid – p + pendimethalin at 2.94 kg ai.ha–1 (2.62 lb ai.A–1) controlled the tested broadleaf and grassy weeds >80% for up to 8 wk following herbicide application. The higher dimethenamid–p + pendimethalin rates of ≥5.88 kg ai.ha–1 (≥5.25 lb ai.A–1) provided 94% to 99% control of the tested weed species but caused commercially unacceptable injury to pygmyweed [Crassula radicans (Haw.) D. Dietr. ‘Red carpet']. Chocolate flower (Berlandiara lyrata Benth.) tolerated dimethenamid–p + pendimethalin at 2.94 kg ai.ha–1 (2.62 lb ai.A–1) and 5.88 kg ai.ha–1 (5.25 lb ai.A–1) but the 11.77 kg ai .ha–1 (10.5 lb ai.A–1) rate was injurious in one of the two study years. Leucothoe [Leucothe fontanesiana (Steudel) Sleumer ‘Rainbow'] showed excellent tolerance to dimethenamid–p + pendimethalin at rates up to 11.77 kg ai.ha–1 (10.5 lb ai .A–1). Herbicides used in this study: 0.75% Dimethenamid–p + 1% pendimethalin (Freehand 1.75 G), (S) 2-chloro-N-(2,4-dimethylthiophen-3-yl)-N-[(2S)-1-methoxypropan-2-yl]acetamide] + N-(1-ethylpropyl)-3,4-dimethyl-2,6- dinitrobenzenamine]. Ornamental plant species used in this study: chocolate flower (Berlandiara lyrata Benth.), leucothoe [Leucothe fontanesiana (Steudel) Sleumer ‘Rainbow'], and pygmyweed [Crassula radicans (Haw.) D. Dietr. ‘Red Carpet']. Weed species used in this study: barnyardgrass [Echinochloa crus-galli (L.) Beauv.], fringed willowherb (Epilobium ciliatum Raf. ssp. ciliatum), giant foxtail (Setaria faberi Hermm.), goosegrass [Elusine indica (L.) Gaertn.], hairy bittercress (Cardamine hirsuta L.), large crabgrass [Digitaria sangunalis (L.) Scop.], redroot pigweed (Amaranthus retroflexus L.), and yellow woodsorrel (Oxalis stricta L.).

Fertilizer placement effects on eclipta (Eclipta prostrata) growth and competition with container-grown ornamentals

AbstractThe objective of this study was to determine the effect of fertilizer placement on the growth of eclipta [Eclipta prostrata (L.) L.] and evaluate its interference with container-grown ornamental plants, including Japanese boxwood (Buxus microphylla Siebold & Zucc.) and ligustrum (Ligustrum lucidum W.T. Aiton). Results indicated that subdressing reduced E. prostrata shoot weight by 28%, 42%, and 46% at depths of 2.5, 5.0, and 7.5 cm, respectively, in comparison with a topdressed fertilizer treatment (a standard industry practice). Presence of E. prostrata reduced the growth of both ornamental species. Ligustrum shoot weight decreased as subdressing depth increased, while boxwood growth was most notably reduced at the 7.5-cm depth in comparison with topdressed containers. Overall, results indicated that subdressing may be an effective weed management strategy, but subdressing depth needs to be based on initial liner size to prevent possibly delays in production time.

Plant Growth and Leachate Electrical Conductivity and pH as Influenced by Controlled-release Fertilizer Blends and Coating Technologies

Although controlled-release fertilizers (CRFs) have been used in container-grown ornamental plants for decades, new coating technologies and blends of fertilizers coated for specific release rates are being employed to customize fertility for specific environments and crops. A study was conducted in the transitional climate of Kentucky to determine the nutrient release rates of three controlled-release blends of 8- to 9-month release and growth response of ‘Double Play Pink’ japanese spirea (Spiraea japonica) and ‘Smaragd’ arbovitae (Thuja occidentalis). Fertilizer 1 (16N–3.5P–8.3K–1.8Mg + trace elements) and Fertilizer 2 (18N–3.1P–8.3K–1.8Mg + trace elements) were prototype blends with different experimental polymer coatings. Fertilizer 3 was a blend of 18N–2.2P–6.6K–1.1Ca–1.4Mg–5.8S + trace elements, which combined 100% resin-coated prills with a polymer coating. Fertilizer 4 was commercially available 15N–3.9P–10K–1.3Mg–6S + trace elements. Fertilizer 3 released its nutrients earlier in the 12-week study than the other three fertilizers and resulted in lower shoot dry weight in both species. The new polymer coating technologies show promise for delivering a predicted release rate and are appropriate for container production of these woody shrubs in Kentucky. An interesting side note of this experiment was that leachate pH measurements across treatments averaged 1.2 units lower for arbovitae (6.3) than for japanese spirea (7.5) at week 12. It was assumed that chemical and/or biological reactions at the root/substrate interface in arbovitae moderated pH increases over the study.

Capture of Sprinkler Irrigation Water by Container-grown Ornamental Plants

The capacity for container-grown plants to capture sprinkler irrigation water plays a critical role in adjusting irrigation rates to deliver required amounts of water to the container substrate. The capture factor (CF) used to describe this capacity was defined as the amount of water captured with a plant relative to the amount captured without a plant. A wind-sheltered, irrigation test area was established to measure CF as affected by plant species, plant size, container size, container spacing, and sprinkler type. CF values for 11 marketable-sized, commonly grown plant species ranged from 1 to 4 with highest values exhibited by plant species with an upright, spreading growth habit. CF values increased as plant size increased. Close container spacings (less than one container diameter between adjacent containers) reduced CF when the allotted area outside the container limited the potential amount of water that could be captured. Compared with impact sprinklers, wobbler sprinklers increased irrigation capture 7% for Ligustrum japonicum grown in 27-cm-diameter containers but not in 16-cm-diameter containers. Results showed that CF is a dynamic parameter that depends on canopy size, container size, container spacing, and sprinkler type. A working knowledge of CF is crucial for determining irrigation requirements to maximize sprinkler irrigation efficiency in container nurseries.

Effects of Fertilization on the Growth and Quality of Container-grown Areca Palm and Chinese Hibiscus during Establishment in the Landscape

The roots of container-grown ornamental plants primarily are concentrated within the original container substrate root ball during the establishment period following transplanting into the landscape. Plants growing in container substrates containing pine bark or peatmoss have higher nitrogen (N) requirements than in most landscape soils due to microbial immobilization of N by these organic components. However, use of high-N fertilizers, such as those used in container production of ornamentals, can cause imbalances with potassium (K) and magnesium (Mg) when used on palms in sandy landscape soils. Areca palm (Dypsis lutescens) and chinese hibiscus (Hibiscus rosa-sinensis ‘President’) that had been growing in containers were transplanted into a landscape soil to determine if high N fertilization during the establishment period could accelerate the rate of establishment without exacerbating K and Mg deficiencies. Although plants of both species had the darkest green color and largest size when continuously fertilized with high N fertilizer, this treatment did induce Mg deficiency in both species. Plant size and color for both species were highly correlated with cumulative N application rates, but also with initial N application rates, suggesting that high N fertilization during the first 6 months affected plant quality at 12 and 24 months after planting, even if high N fertilization was discontinued. However, continued use of a moderate N landscape palm maintenance fertilizer ultimately produced areca palm plants as good as those receiving high N during the establishment period.

Root Zone Sensors for Irrigation Management in Intensive Agriculture

Crop irrigation uses more than 70% of the world’s water, and thus, improving irrigation efficiency is decisive to sustain the food demand from a fast-growing world population. This objective may be accomplished by cultivating more water-efficient crop species and/or through the application of efficient irrigation systems, which includes the implementation of a suitable method for precise scheduling. At the farm level, irrigation is generally scheduled based on the grower’s experience or on the determination of soil water balance (weather-based method). An alternative approach entails the measurement of soil water status. Expensive and sophisticated root zone sensors (RZS), such as neutron probes, are available for the use of soil and plant scientists, while cheap and practical devices are needed for irrigation management in commercial crops. The paper illustrates the main features of RZS’ (for both soil moisture and salinity) marketed for the irrigation industry and discusses how such sensors may be integrated in a wireless network for computer-controlled irrigation and used for innovative irrigation strategies, such as deficit or dual-water irrigation. The paper also consider the main results of recent or current research works conducted by the authors in Tuscany (Italy) on the irrigation management of container-grown ornamental plants, which is an important agricultural sector in Italy.

Effectiveness of Pasteurized Poultry Litter as a Partial Substitute for Controlled-release Fertilizers in the Production of Container-grown Ornamental Plants

In two experiments, pasteurized poultry litter (PPL) was evaluated as a potential substitute for controlled-release fertilizers in the production of container-grown downy jasmine (Jasminum multiflorum), chinese hibiscus (Hibiscus rosa-sinensis), and areca palm (Dypsis lutescens). Downy jasmine and chinese hibiscus generally grew better when provided with PPL as a micronutrient source than with no micronutrients or with an inorganic micronutrient blend (MN). However, areca palm grew poorly with PPL as a fertilizer supplement compared with MN-fertilized areca palm. PPL provided high levels of ammonium nitrogen, phosphorus, and potassium during the first few weeks, but soil solution levels of these elements dropped off rapidly in subsequent weeks. The large amount of phosphorus leached from the containers fertilized with PPL is an environmental concern.

Leaf-Waste Pellets as a Herbicide Carrier for Container-Grown Ornamental Plants

An organic herbicide carrier could help reduce misapplication and environmental pollution associated with spray application of herbicides. Pellets prepared from landscape leaves that were dried, ground, and pelletized were evaluated as a preemergence herbicide carrier for container-grown ornamental plants. Isoxaben, pendimethalin, and prodiamine at rates of 1.12, 2.25, and 2.25 kg ai/ha, respectively, with either water or landscape leaf-waste pellets as a carrier were applied to chrysanthemum ‘Lisa’, spirea ‘Neon Flash’, and wintercreeper ‘Coloratus’. Common groundsel, common purslane, and giant foxtail were seeded following herbicide application. Leaf-waste pellets as a carrier produced equivalent efficacy and phytotoxicity ratings to conventional spray application of pendimethalin and prodiamine on both chrysanthemum and wintercreeper. The leaf-waste pellets were not an effective carrier for the application of isoxaben alone. The pellets had inconsistent effects on spirea phytotoxicity and growth.

(82) Determining Effects of a Uniconazole Drench on Celosia, Petunia, Salvia, and Tagetes

Uniconazole is a plant growth regulator used to inhibit internode elongation on container-grown ornamental plants. Uniconazole is effective on a wide range of plants, but is not commonly used on bedding plants because of concerns about stunting and flowering delay. Our objective was to determine the effectiveness of uniconazole when used as a drench, eliminating the variability inherent in a spray application. Seedlings of Celosia argentea L. var. plumosa L. `Fresh Look Red', Petunia ×hybrida Vilm.-Andr. `Prostrate Wave Rose', Salvia splendens Sell ex Roem. & Schult. `Vista Red', and Tagetes erecta L. `Inca II Gold' in 288-cell plug trays were transplanted 2 days after arrival into 10-cm pots filled with a soilless medium containing no bark. Plants were placed in a greenhouse with a setpoint of 20 °C and under a 16-h photoperiod provided by high-pressure sodium lamps. A single drench application of 0, 0.04, 0.07, 0.15, or 0.30 mg active ingredient/pot was made 11 days after transplant. The uniconazole drench inhibited internode elongation in these species and higher rates provided a greater degree of response. At time of flowering, the 0.30-mg uniconazole drench inhibited shoot length in Celosia, Petunia, Salvia, and Tagetes by 36%, 23% 26%, and 13%, respectively. Drenches of 0.04 or 0.07 mg provided a desirable degree of height control for Celosia and Salvia. For vigorous species like Petunia or Tagetes, 0.15 to 0.30 mg may be more appropriate. We observed a 1- or 2-day delay in flowering of Salvia and Tagetes plants drenched with 0.30 mg, but no delays in Petunia flowering.

Chemical and physical properties of pruning waste compost and their seasonal variability

Selected chemical and physical properties of 12 different pruning waste compost (PWC) samples were evaluated to assess their suitability as substrates for ornamental plants. Samples were taken periodically from the same composting facility over 18 months in order to determine if there was any seasonal variability. In addition to the PWC samples, a Canadian Sphagnum peat and a commercial growing medium (CGM) were used as standard materials. With respect to PWC properties, pH values were above 8, significantly higher than the pH of peat and the commercial substrate. All samples showed adequate levels of organic matter and correspondingly high cation-exchange capacity (CEC) values. The C/N ratio varied between 22 and 48, significantly higher than the optimal values of 15–20. Although composts were sampled from piles established in different seasons, no significant differences were found in their chemical properties. However, water retention characteristics were affected by seasonal changes in components entering the facility. Comparing the properties of PWC to those of peat and commercial growing medium, this material appears to be an acceptable component of a substrate for container-grown ornamental plants.

Choice of Adjuvant with Halosulfuron Affects Purple Nutsedge Control and Nursery Crop Tolerance

One-half (18 g·ha-1 a.i.) and three-fourths (27 g·ha-1 a.i.) rates of halosulfuron (Manage®, MON 12051) were combined with adjuvants and evaluated for effectiveness in controlling purple nutsedge (Cyperus rotundus L.) and for phytotoxic responses exhibited by two kinds of container-grown ornamental plants. Adjuvants included X-77®, Scoil®, Sun-It II®, Action “99”®, and Agri-Dex®. By 8 weeks after treatment (WAT), halosulfuron combined with X-77®, Agri-Dex®, or Action “99”® at the lower halosulfuron rate provided <90% purple nutsedge suppression. In contrast, Sun-It II® provided 100% control when combined with the higher halosulfuron rate. Nutsedge control persisted into the following growing season and halosulfuron combined with either Scoil® or Sun-It II® provided >97% suppression of nutsedge tuber production. Growth of liriope [Liriope muscari (Decne.) Bailey `Big Blue'] was not inhibited by Scoil® or Sun-It II® adjuvants in combination with the low rate of halosulfuron. However, regardless of the rate of halosulfuron or adjuvant used, initial foliar chlorosis was observed in both daylily (Hemerocallis sp. L. `Stella d'Oro') and liriope. All liriope receiving halosulfuron with X-77®, Scoil®, or Sun-It II® adjuvants recovered normal foliage by 8 WAT. By contrast, at 8 WAT some daylily still maintained a degree of foliar discoloration. In addition to chlorosis, all treatments reduced flower number in daylilies. The number of flower scapes produced by liriope was not affected by halosulfuron when in combination with either Sun-It II® or Scoil®. The high rate of halosulfuron combined with X-77® or Action “99”® improved control of purple nutsedge. However, this rate inhibited growth of both species, daylily flower numbers, and scape numbers of liriope, regardless of adjuvant. Chemical names used: halosulfuron (Manage®, MON 12051, methyl 5-{[(4,6-dimethyl-2-pyrimidinyl) amino] carbonyl-aminosulfonyl}-3-chloro-1-methyl-1-H-pyrozole-4-carboxylate); proprietary blends of 100% methylated seed oil (Scoil® and Sun-It II®); proprietary blend of 99% polyalkyleneoxide modified heptamethyl trisiloxane and nonionic surfactants (Action “99”®); alkylarylpolyoxyethylene, alkylpolyoxyethelene, fatty acids, glycols, dimethylpolysiloxane, and isopropanol (X-77®); proprietary blend of 83% paraffin-based petroleum oil, with 17% polyoxyethylate polyol fatty acid ester and polyol fatty ester as nonionic surfactants (Agri-Dex®)

380 Differential Responses of Container-grown Ornamental Foliage Plants to Silicon Application

Silicon (Si) is the second most-abundant element in soils, and its concentration in soil solution ranges from 0.1 to 0.6 mm, which is the same concentration range as some of the major nutrient elements such as calcium, magnesium, phosphorus, and sulfur. Increasing evidence has recently suggested that Si plays important roles in improving plant growth. However, little information is available on Si effects on container-grown ornamental plants, particularly since most are grown in soilless media where Si sources are greatly limited. The objectives of this research were to evaluate Si absorption and translocation in diverse container-grown ornamental plants and to determine whether Si absorption could improve plant growth. Liners from 39 plant species were potted in peat and pine bark-based soilless media and grown in a shaded greenhouse. Plants were fertigated with a Peter's 24–8–16 water-soluble fertilizer containing 0, 50, and 100 mg·L–1 of Si. Once marketable sizes were reached, plants were harvested and fresh and dry weights determined; Si and other nutrient elements in roots and shoots were measured. Results indicated that 32 of the 39 evaluated species were able to absorb Si, with large quantities further transported to shoots. Of the 32 Si-responsive species, 17 showed significant dry weight increases, whereas the other 15 only exhibited Si absorption and translocation with no apparent growth responses. The seven non-responsive plant species showed no significant increases in neither Si absorption and translocation, nor dry weight.

SOIL MOISTURE TENSION-BASED IRRIGATION OF CONTAINER-GROWN PLANTS UNDER COMMERCIAL CONDITIONS.

An irrigation system was developed to water container-grown ornamental plants so that soil moisture tensions could be continuously monitored and controlled. Operation of such a system has been shown to significantly reduce the amount of water which must be applied to produce high-quality potted chrysanthemums. This presentation will focus on modification of drip irrigation systems in commercial production environments to irrigate based on soil moisture tension. High-quality plants were produced in commercial trials with such systems. In all cases significant economic savings due to reduced fertilizer and water application were observed. Furthermore, the amounts of irrigation water run-off were significantly lower than in systems where irrigation was controlled manually or with timers.

Evaluation of oxadiazon and simazine for weed control and phytotoxicity in container-grown ornamental plants

Granular formulations of oxadiazon alone and oxadiazon plus simazine were applied at three rates to 16 species of Australian native and exotic ornamental plants. Oxadiazon alone (2, 4 or 8 kg ha −1) produced no symptoms of phytotoxicity or reduced shoot dry weight (SDW) in any species. The combination of oxadiazon and simazine (4.0 + 1.0 or 8.0 + 2.0 kg ha −1, respectively) produced leaf-burn in half of the species and depressed SDW in Dampiera, Grevillea ‘Boongala Spinebill’, G. hookerana, G. ‘Pink Lady’, G. ‘Royal Mantle’, Helichrysum and Westringia. Even the lowest rate of oxadiazon and simazine (2.0 + 0.5 kg ha −1, respectively) reduced the SDW of Grevillea ‘Royal Mantle’, G. ‘Boongala Spinebill’ and Helichrysum. All herbicides provided >90% control of summer grass ( Digitaria sanguinalis), bittercress ( Cardamine hirsuta) and willow herb ( Epilobium sp.). None of the herbicide treatments significantly reduced the number of weeds of chickweed ( Stellaria media). There were no significant differences between herbicide types in the control of mouse-eared chickweed ( Cerastium glomeratum), but there was a significant herbicide-rate effect. The middle and highest rates provided 40 and 92% control, respectively.

An evaluation of pre-emergent herbicides for container-grown ornamental plants

Two applications of 5 herbicides were evaluated during spring and summer for weed control and phytotoxicity on 25 species of trees, shrubs and herbaceous perennials. Weed control was considered to be effective if herbicide-treated pots contained at most 20% of the weeds in untreated pots. Oxyfluorfen applied at 1.25, 2.5 and 5.0 kg ha −1 provided effective control of grass and broad-leaved weeds for 8 weeks after the first application, and the 2 higher rates effectively controlled all weeds for 12 weeks after the second application. Oxadiazon at 2.0, 4.0 and 8.0 kg ha −1 effectively controlled all weeds for 8 weeks after the first application, but only the highest rate was effective 12 weeks after the second application. Napropamide at 5.0, 10.0 and 20.0 kg ha −1 effectively controlled grasses for up to 12 weeks, but only effectively controlled broad-leaved weeds at the 2 higher rates for 8 weeks after the first application and failed to control them after the second application. Alachlor at 4.0, 8.0 and 16.0 kg ha −1 and oryzalin + trifluralin at 0.5, 1.0 and 2.0 kg ha −1 provided effective control of grasses for 8 weeks after the first application. These herbicides at the highest rate also controlled broad-leaved weeds for 8 weeks after the first application. However alachlor and oryzalin + trifluralin failed to provide effective control of any weeds after the second application. Competition from weeds reduced the shoot dry weight (SDW) of unweeded control pots by 20% compared with hand-weeded control pots. None of the herbicides produced visible clamage in any plants. The SDW of 8 species treated with some of the herbicides was significantly lower than the corresponding hand-weeded control plants, and for 6 of these species some herbicide treatments were identified as being possibly phytotoxic. Oxyfluorfen appeared to inhibit the growth of Photinia and Coleonema, and alachlor inhibited the growth of Photinia, Eriostemon, Azalea ‘Splendens’, Lavendula and Coleonema. Oryzalin + trifluralin appeared to inhibit the growth of Bauhinia, and napropamide and oxadiazon inhibited the growth of Coleonema.

Relative Water Demand in Container-grown Ornamental Plants

Abstract Relative water use patterns for 12 species of container-grown ornamental plants, areca palm (Chrysalidocarpus lutescens Wendl.), ficus (Ficus benjamina L.), gumbo-limbo [Bursera simaruba (L.) Sarg.], parlor palm (Chamaedorea elegans Mart.), paurotis palm [Acoelorrhaphe wrightii (Griseb. + Wendl.) Wendl. ex Becc.], philodendron (Philodendron selloum Koch), pigeon plum (Coccoloba diversifolia Jacq.), schefflera (Brassaia actinophylla Endl.), seagrape [Coccoloba uvifera (L.) L.], silver buttonwood (Conocarpus erectus var. sericeus Fors, ex DC.), silver palm [Coccothrinax argentata (Jacq.) Bailey], and West Indian mahogany [Swietenia mahagoni (L.) Jacq.] were measured by comparison of actual water consumption with growth rates and predicted potential evapotranspiration rates. Growth rates as determined by the change in size index over time were used to characterize species as slow, moderate, or fast-growing. The lowest relative water demand was seen in the slow-growing species. Highest relative water demand occurred in the moderate and fast-growing species. Certain moderate and fast-growing plants such as West Indian mahogany, philodendron, and pigeon plum exhibited relative water demand rates not significantly different from the slow-growing species. Monthly potential evapotranspiration rates were closely related to actual irrigation demand levels in all 12 species.