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Imazapic is an acetolactate synthase-inhibiting herbicide labeled for weed control in pastures, rangeland, and noncrop areas. Field research was conducted in Knoxville, TN, USA, during 2020 and 2021 to evaluate the tolerance of four hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis Burtt Davy) cultivars to applications of imazapic for growth suppression. Separate experiments were conducted on ‘TifTuf’, ‘Tifway’, ‘Tahoma 31’, and ‘Latitude 36’ hybrid bermudagrass. Experiments included plots (1.5 m2) arranged in a randomized complete block design with four replications and were repeated. Treatments were applied 14 Aug 2020 and 6 Aug 2021, and were mixed with methylated seed oil. Imazapic rates were 0, 35, 52.5, 70, or 105 g⋅ha–1. Cultivar tolerance was assessed via visual ratings of turfgrass injury relative to untreated check plots. Normalized differential vegetation index data were collected on each date turfgrass injury was evaluated. Growth suppression was quantified via reductions in dry clipping weight after mowing. Hybrid bermudagrass injury increased with imazapic rate for all cultivars, and peak injury (> 30%) following all imazapic treatments occurred within 14 days. At the lowest imazapic rate (35 g⋅ha–1), injury was transient, with all hybrid bermudagrass cultivars fully recovered by 28 days. All rates of imazapic reduced hybrid bermudagrass dry clipping weight for 21 days for all cultivars. Further research is warranted to explore lower application rates than those tested in our study, in addition to determining tolerance and growth suppression of other turfgrass species commonly managed on golf courses.

Open Access

Warmer temperatures during crop production are not desirable for a cool-season crop such as lettuce (Lactuca sativa L.). Lettuce is among the top 10 most consumed vegetables in the United States. Production of this vegetable is concentrated mostly in temperate areas of California, and during the wintertime in Arizona and Florida as a result of their mild climatic conditions. Heat-tolerant cultivars are needed for the leafy vegetable industry to continue thriving. However, there is very little information on heat-tolerant germplasms of lettuce that can be used as a source to improve heat tolerance in lettuce. This is particularly important in romaine and butterhead lettuce, which are two morphological types with increasing demand in the market. Therefore, research was conducted to identify germplasm that performs acceptably in warmer regions in the western United States. This investigation also aimed to understand the reaction of varieties to different environments, which could help plant breeders select and evaluate lettuce plants during the breeding process. Twenty-three and 25 accessions of romaine and butterhead lettuce, respectively, were planted in five trials near Holtville, CA, USA: Five Points, CA, USA, under warmer temperatures and Salinas, CA, USA, under cooler temperatures. Romaine genotypes Bambi, Blonde Lente a Monter, Medallion MT, and Red Eye Cos; and butterhead genotypes Butter King and Margarita had no bolting, an acceptable head weight, short cores, and acceptable head height. Head weight and related traits (including core length, height, width, etc.) and heat-related disorders were significantly different across multiple experiments, indicating genetic variation. The major component of the phenotypic variation in these experiments was a result of environmental factors. Therefore, plant breeders may still need to evaluate progeny in multiple trials and multiple locations to select heat-tolerant romaine and butterhead lettuce effectively.

Open Access

Humic substances are components of soil organic matter that influence soil structure and fertility. Humic and fulvic acids can be extracted from soil and other organic sources, and are used as biostimulants to promote plant growth and increase nutrient availability and uptake. The goal of this study was to determine whether selected humic and fulvic acid–based commercial products would promote growth and flowering of petunia (Petunia ×hybrida) ‘Picobella Blue’ grown in soilless media with low or optimal fertilizer rates. Plants were grown in 11.4-cm pots filled with peat-based media [80:20 peat:perlite (v/v); pH 5.4]. Three biostimulant products were evaluated at different rates and application frequencies: Huma Pro, a liquid humic acid biostimulant; Fulvi Pro, a liquid fulvic acid biostimulant; and Micromate, a powder containing both humic and fulvic acids. In Expt. 1, Huma Pro and Fulvi Pro were drenched weekly onto the growing media at a rate of 5, 10, or 20 mL⋅L–1; Micromate was drenched weekly at a rate of 5, 10, 20, or 40 g⋅L–1. Plants were fertilized with either 50 mg⋅L–1 nitrogen (N) (low fertility) or 100 mg⋅L–1 N (optimal fertility) from Jack’s Professional 20N–1.3P–15.7K Petunia FeED each irrigation. Control plants received fertilizer but no biostimulant treatments. In Expt. 2, biostimulant treatments were drenched once at transplant, biweekly, or weekly at a rate of 1.25, 2.5, 5, or 10 mL⋅L–1 for Huma Pro and Fulvi Pro; and at 5, 10, 20, or 40 g⋅L–1 for Micromate. All plants received constant liquid feed at the lower fertilizer rate of 50 mg⋅L–1 N. In Expt. 1, plants fertilized with 100 mg⋅L–1 N and treated with 20 g⋅L–1 Micromate had the best performance. The average shoot dry weight was 32% greater than that of the control plants. Micromate (20 g⋅L–1)-treated plants had an average of five more flowers per plant, and they flowered 4 days earlier than untreated control plants. In Expt. 2, plants treated with 40 g⋅L–1 of Micromate weekly had the greatest shoot dry weight compared with the other treatments. Weekly Micromate treatments (40 g⋅L–1) resulted in plants with an average of 13 more flowers per plant, which flowered 7 days earlier than control plants. Plants treated with Fulvi Pro and Huma Pro at 20 mL⋅L–1 had a significantly greater concentration of potassium in shoot tissue, whereas Micromate treatments at 20 and 40 g⋅L–1 resulted in a greater concentration of phosphorous in the shoots. The humic and fulvic acids in Micromate improved petunia crop quality by promoting vegetative growth, increasing flower numbers, and reducing the time to flower.

Open Access

Onions (Allium cepa) are typically planted late fall and harvested in spring in the Vidalia, GA, USA, region. Onions grown here are renowned for their for sweetness and are marketed to consumers as Vidalia onions. High rainfall during the relatively long growing season (4 to 5 months) may result in nitrogen (N) leaching during production. Therefore, fertilizer applications are usually aligned with stages of crop development to ensure nutrient availability for the entire season. Although the impacts of N application rate have been previously investigated for Vidalia onion production, the optimal timing for the final N application of the season has not been determined. The objectives of this study were to determine the optimal timing of the last fertilizer N application (at bulb initiation, during bulb growth, or during bulb maturation) in conjunction with the impact of three N application rates (75, 105, and 135 lb/acre N) on yield and quality in Vidalia onion. Soil N levels were affected by N rate, year, and onion growth stage. In 2020, up to 135 lb/acre N was required to maximize onion yields, and in 2021, onion yields were unchanged among N fertilizer treatments. Final N applications at bulb initiation resulted in greater yields than applications made during bulb growth or bulb maturation. In addition, as the N rate increased and the time of final application occurred later in bulb development, pungency values increased. Incidence of sour skin (Burkholderia cepacia) and center rot (Pantoea sp.) diseases were greater in 2020 compared with 2021 and seemed to be affected by environmental conditions more than N fertilization.

Open Access

Cultural and environmental factors can place creeping bentgrass (Agrostis stolonifera) under extreme stress during the summer months. This stress, coupled with the growth adaptation of creeping bentgrass, can result in shallow, poorly rooted stands of turf. To enhance root zone oxygen and rooting of creeping bentgrass, golf courses use methods such as core and solid-tine aerification, and sand topdressing. An additional method of delivering oxygen to the soil could be irrigation with nanobubble-oxygenated water. The properties of nanobubbles (NBs) allow for high gas dissolution rates in water. Irrigating with NB-oxygenated water sources may promote increased rooting of creeping bentgrass putting greens during high-temperature periods and lead to a more resilient playing surface. The objectives of this study include comparing the effects of irrigation with NB-oxygenated water sources with untreated water sources on creeping bentgrass putting green root zone and plant health characteristics using field and controlled environment experiments. Treatments included NB-oxygenated potable water and irrigation pond water, and untreated potable and irrigation pond water. In the field, NB-oxygenated water did not enhance plant health characteristics of creeping bentgrass. In 1 year, NB-oxygenated water increased the daily mean partial pressure of soil oxygen from 17.48 kPa to 18.21 kPa but soil oxygen was unaffected in the other 2 years of the trial. Subsurface irrigation with NB-oxygenated water did not affect measured plant health characteristics in the greenhouse. NB-oxygenation of irrigation water remains an excellent means of efficiently oxygenating large volumes of water. However, plant health benefits from NB-oxygenated irrigation water were not observed in this research.

Open Access

To align with global trends and the swift pace of technological advancements, it is imperative to consistently update the professional standards and curriculum for horticultural therapists to meet evolving professional demands. This study used the developing a curriculum (DACUM) method to analyze the tasks and duties of Korean horticultural therapists and subsequently tailor a specialized training program for them. First, 11 experts in the horticultural therapy field participated in workshops to develop a DACUM chart that included the definitions, tasks, knowledge, skills, and attitudes of horticultural therapists. A job performance evaluation survey for horticultural therapists was also developed through these workshops. The 300 participants of the online survey were members of the Korea Horticultural Therapy and Welfare Association. The survey consisted of a 5-point Likert scale of the current performance level and future requirement level for each qualification grade. Demographic information and responses to each question were computed using a frequency analysis and percentages, grade-specific task performance evaluations comprised a one-way batch analysis of variance, and statistical significance levels were set to P < 0.05. The horticulture professional curriculum was based on competencies derived from the job analysis and online conferences with 10 professionals who participated in the DACUM workshops. The job analysis results revealed six duties with a total of 32 tasks. The results of the job performance evaluation showed that there was a great demand for the development of their convergence capabilities. Accordingly, in response to these results, new interdisciplinary convergence fields such as horticultural therapy and science (information technology), horticultural therapy, and humanities education were introduced into the specialized training. The results of this study will be valuable for improving the skills and expertise of horticulture therapists to meet social needs.

Open Access

Compared with the ambient Earth carbon dioxide concentration (≈415 μmol⋅mol–1), the International Space Station has superelevated carbon dioxide (≈2800 μmol⋅mol–1), which can be a stressor to certain crops. Far-red light can drive plant photosynthesis and increase extension growth and biomass. However, the effects of far-red light under superelevated carbon dioxide are unclear. We grew hydroponic mustard (Brassica carinata) ‘Amara’ seedlings in four growth chambers using a randomized complete block design with two carbon dioxide concentrations (415 and 2800 μmol⋅mol–1), two lighting treatments, and two blocks at temperature and relative humidity set points of 22 °C and 40%, respectively. Each growth chamber had two lighting treatments at the same total photon flux density of 200 μmol⋅m–2⋅s–1. Under the same blue and green light at 50 μmol⋅m–2⋅s–1 each, plants received either red light at 100 μmol⋅m–2⋅s–1 or red + far-red light at 50 μmol⋅m–2⋅s–1 each. At day 15 after planting, far-red light did not influence shoot fresh or dry mass at 415 μmol⋅mol–1 carbon dioxide, but decreased both parameters by 22% to 23% at 2800 μmol⋅mol–1 carbon dioxide. Increasing the carbon dioxide concentration increased shoot fresh and dry mass 27% to 49%, regardless of the lighting treatment. Far-red light decreased leaf area by 16% at 2800 μmol⋅mol–1 carbon dioxide, but had no effect at 415 μmol⋅mol–1 carbon dioxide. Increasing the carbon dioxide concentration increased leaf area by 21% to 33%, regardless of far-red light. Regardless of the carbon dioxide concentration, far-red light promoted stem elongation and decreased chlorophyll concentrations by 39% to 42%. These responses indicate far-red light elicited a crop-specific shade avoidance response in mustard ‘Amara’, increasing extension growth but decreasing leaf area, thereby reducing light interception and biomass. In addition, carbon dioxide enrichment up to 2800 μmol⋅mol–1 increased the biomass of mustard ‘Amara’ but decreased the biomass of other crops, indicating crop-specific tolerance to superelevated carbon dioxide. In conclusion, mustard ‘Amara’ seedlings benefit from superelevated carbon dioxide, but exhibit growth reduction under far-red light under superelevated carbon dioxide.

Open Access

Various soilless substrate components have been evaluated for many years to identify sustainable resources that do not negatively impact plant growth. Biochar is a carbon-based material that has been evaluated for use as an alternative aggregate in peat-based soilless substrates. In addition, the use of carbon adsorption for compound removal is widely used in groundwater remediation, municipal water filtration, and volatile organic compounds. Experiment one aimed to determine the impact of coarse biochar (<6 mm) on paclobutrazol efficacy when incorporated at 15% or 30% by volume in a peat-based substrate when compared with a perlite-amended substrate at the same incorporation volumes. In Expt. 1, a single paclobutrazol drench application of 0, 0.5, 1.0, 2.0, and 4.0 mg·L−1 was applied to ‘Princettia Red’ and ‘Princettia White’ poinsettias (Euphorbia pulcherrima × Euphorbia cornastra). In Expt. 2, two different biochar particle sizes of coarse (<6 mm) and extra coarse (>6 mm) were examined at the same incorporation volumes as Expt. 1 and compared with a perlite-amended substrate at the same incorporation volumes. However, during Expt. 2, continual drench applications at times of irrigation of 0.0, 6.25, 12.5, 25.0, 50, and 100 μg·L−1 (ppb) paclobutrazol were applied to pansy (Viola ×wittrockiana) ‘Matrix Blue Blotch’ and begonia (Begonia ×hybrida) ‘Big Red Bronze Leaf’. The efficacy of paclobutrazol drenches for controlling growth in all species was unaffected by the substrate composition regarding aggregate type or aggregate incorporation rate. Thus, even though biochar is often used for bioremediation and wastewater treatment, it did not negatively impact the efficacy of paclobutrazol drenches at the concentrations used. This research suggests that when biochar is used as an amendment to peatmoss it will not influence paclobutrazol drench efficacy when incorporated up to 30% by volume for the examined species.

Open Access

Traffic injury caused by foot- or athlete-surface interaction is one of the most critical problems athletic field managers face in maintaining the surface playability and aesthetic quality of athletic fields. Bermudagrass (Cynodon spp.) is the most widely used turfgrass species on athletic fields in the transitional climatic zone. A 2-year field study was conducted to evaluate nine bermudagrass cultivars for their persistence and surface playability under simulated fall cleat traffic. The experiment was conducted in Stillwater, OK, on a natural loam soil. Treatments were arranged as a split-block design with three replications. Traffic was applied for 6 weeks in Fall 2019 and 2020 using a Baldree traffic simulator, which generated 10 traffic events per week; each traffic event resulted in 678 cleat marks/m2. ‘Bimini’ was generally found to be the most persistent grass under traffic for aesthetic properties, and ‘Astro’ and ‘Tifway’ were the least persistent. Surface playability was affected by simulated traffic stress as shear strength (SS) declined and surface hardness (SH) increased, over time. ‘Bimini’ had greater SS than ‘Astro’ and ‘OKC1131’ (Tahoma 31®) by 1.9 and 1.4 N·m, respectively. SS of ‘DT-1’ (TifTuf®) and Tahoma 31 and SH of ‘OKC1134’ (NorthBridge®) were least affected by simulated traffic stress. Overall, surface playability characteristics of NorthBridge, ‘Bimini’, ‘OKC1119’ (Latitude 36®), TifTuf, Tahoma 31, and ‘Riley Riley’s Super Sport’ (Celebration®) were least affected by traffic. Findings illustrate bermudagrass cultivars can vary in visual persistence and surface playability.

Open Access