Clematis (Clematis ×hybrida) is among the flowering plants well-recognized by the retail consumer; however, production has not traditionally fit into standard greenhouse production systems. One reason is the relatively long 2-year production cycle from propagation to flowering. Four experiments were conducted with clematis ‘H.F. Young’ to understand the factors that influence shoot development and flowering of clematis so that strategies could be developed for bulking, providing a cold treatment, and flowering the plants with a shortened production time. The first experiment showed an increase in shoot and flower numbers and a decrease in time to flower as the duration of cold treatment increased from 0 to 9 weeks and the photoperiod increased from 9 to 16 hours. The second experiment resulted in greater shoot and flower numbers when plants were forced at 21 °C as compared with 27 °C. The third experiment showed that the application of ethephon (500 or 1000 mg·L−1) during bulking increased shoot formation (branching) as compared with the control or 500 mg·L−1 benzylaminopurine treatments. The fourth experiment showed that applications of 500 mg·L−1 ethephon along with a 16-hour photoperiod during the bulking period improved shoot number and flowering of the finished crop. The combined results provide guidelines for producing a well-branched, flowering clematis crop within 1 year from the start of propagation to the time of the first open flower.
Uttara C. Samarakoon and James E. Faust
Julieta Trevino Sherk, Wenyan Fu, and Joseph C. Neal
Compared with traditional roofing, green roofs (GRs) have quantifiable environmental and economic benefits, yet limited research exists on GR plant survival, maintenance practices, and costs related to plant performance. The objective of this study was to assess plant cover, site conditions, and maintenance practices on 10 extensive GRs in the Research Triangle Area of North Carolina. Green roof maintenance professionals were surveyed to assess plant performance, maintenance practices, and maintenance costs. Vegetation cover on each site was characterized. Relationships among plant performance and environmental and physical site characteristics, and maintenance practices were evaluated. Survey respondents ranked weed control as the most problematic maintenance task, followed by irrigation, pruning, and debris removal. No single design or maintenance factor was highly correlated with increased plant cover. Green roof age, substrate organic matter, and modular planting methods were not correlated with greater plant cover. Results showed a trend that irrigation increased plant cover. Plants persisting on GRs included several species of stonecrop (Sedum sp.), but flame flower (Talium calycinum) and ice plant (Delosperma basuticum) were also present in high populations on at least one roof each. Green roof maintenance costs ranged from $0.13/ft2 to $3.45/ft2 per year, and were greater on sites with more weeds and frequent hand watering.
Hunter A. Hammock, Dean A. Kopsell, and Carl E. Sams
Light emitting diodes (LEDs) can produce a wide range of narrowband wavelengths with varying intensities. Previous studies have demonstrated that supplemental blue (B) and red (R) wavelengths from LEDs impact plant development, physiology, and morphology. High-pressure sodium (HPS) lighting systems are commonly used in greenhouse production, but LEDs have gained popularity in recent years because of their improved energy efficiency and spectral control. Research is needed to determine the efficacy of supplementary B and R LED narrowband wavelengths compared with traditional lighting systems like HPS in terms of yield, quality, and energy consumption for a variety of greenhouse-grown high-value specialty crops. The objective of this study was to determine the impact of LED and HPS lighting on greenhouse hydroponic basil (Ocimum basilicum var. ‘Genovese’) biomass production and edible tissue nutrient concentrations across different growing seasons. Basil was chosen because of its high demand and value among restaurants and professional chefs. A total of eight treatments were used: one nonsupplemented natural light (NL) control; one HPS treatment; and six LED treatments (peaked at 447 nm/627 nm, ±20 nm) with progressive B/R ratios (10B/90R; 20B/80R; 30B/70R; 40B/60R; 50B/50R; and 60B/40R). Each supplemented light (SL) treatment provided 8.64 mol·m−2·d−1 (100 µmol·m−2·s−1, 24 h·d−1). The daily light integral (DLI) of the NL control averaged 9.5 mol·m−2·d−1 across all growing seasons (ranging from 4 to 18 mol·m−2·d−1). Relative humidity averaged 50%, with day/night temperatures averaging 27.4 °C/21.8 °C, respectively. LED treatments had the greatest total fresh biomass (FM) and dry biomass (DM) accumulation; biomass for LED treatments were 1.3 times greater on average than HPS, and 2 times greater than the NL control. Biomass partitioning revealed that the LED treatments had more FM and DM for the individual main stem, shoots, and leaves of each plant at varying levels. LED treatments resulted in greater height and main stem diameter. Some essential nutrient concentrations were impacted by SL treatments and growing season. An energy analysis revealed that on average, narrowband B/R LED treatments were 3 times more energy efficient at increasing biomass over HPS. LED treatments reduced SL energy cost per gram FM increase by 95% to 98% when compared with HPS. In addition, the rate of electricity consumption to biomass increase varied across LED treatments, which demonstrates that basil uses different B/R narrowband ratios at varying efficiencies. This experiment shows that spectral quality of both supplemental sources and natural sunlight impacts primary metabolic resource partitioning of basil. The application of LED lighting systems to supplement natural DLI and spectra during unfavorable growing seasons has the potential to increase overall biomass accumulation and nutrient concentrations in a variety of high-value specialty crops.
Arthur Villordon, Jeffrey C. Gregorie, and Don LaBonte
The primary objective of this work was to generate species-specific information about root architectural responses to variations in inorganic phosphate (Pi) availability at the onset of storage root formation among six sweetpotato (Ipomoea batatas) cultivars. Three Pi levels were used: 0 (low Pi); 0.17 (medium Pi); and 0.34 (high Pi) g/pot triple super phosphate (0N–46P–0K). The check cultivar ‘Bayou Belle’ (BB) consistently showed evidence of storage root formation at 15 days in adventitious roots (ARs) grown across three Pi levels and two planting dates (PDs). Storage root formation was also detected in ‘Orleans’ (OR) and ‘Beauregard’ (BX), but it was less consistent relative to BB. In general, BB had the lowest adventitious root (AR) number relative to the other cultivars, but the magnitudes of difference varied with Pi availability and PD. With the first PD, BX had a 45% higher AR number compared with BB in low Pi conditions; however, there were no differences in the second PD. Within cultivars, BX and Okinawa grown in low Pi showed combined 17% and 24% reductions in primary root length (PRL) relative to roots grown in high Pi. BB had a higher lateral root number (LRN) and lateral root density (LRD) across Pi levels, corroborating prior data regarding the association of these root architectural attributes with the onset of storage root formation. The experimental data support the hypothesis regarding the existence of genetic variation for Pi efficiency in sweetpotato and that some well-documented Pi-efficient root traits like high LRN and LRD are indirectly selected for in-breeding programs that focus on early storage root formation and stable yields across environments.
Richard P. Marini, Tara Auxt Baugher, Megan Muehlbauer, Sherif Sherif, Robert Crassweller, and James R. Schupp
‘Honeycrisp’ (Malus ×domestica) apples were harvested from a total of 17 mid-Atlantic orchards during 2018 and 2019 to verify a previously published bitter pit prediction model. As in the previous study, bitter pit incidence was associated with low calcium (Ca) levels and high ratios of nitrogen (N), potassium (K), and/or magnesium (Mg) to Ca in the fruit peel and excessive terminal shoot growth. The best two-variable model for predicting bitter pit developed with the 2018–19 data set contained boron (B) and the ratio of Mg to Ca (R 2 = 0.83), which is different from previous models developed with data from three individual years (2015–17). When used to predict the bitter pit incidence of the 2018–19 data, our previous best model containing the average shoot length (SL) and the ratio of N to Ca underestimated the incidence of bitter pit. The model is probably biased because one or more important variables related to bitter pit have not yet been identified. However, the model is accurate enough to identify orchards with a low incidence of bitter pit.
Jing Wu, Qi He, Caihong Zhang, and Gui Wang
Eric T. Stafne
Since late Mar. 2020, many universities halted normal operations due to the Coronavirus Disease 2019 (COVID-19) pandemic. Although extension uses many different techniques to educate consumers, it has been slow to grasp the power of social media. Faced with a dilemma of using digital methods instead of in-person field days, short courses, and workshops, Twitter was a viable alternative, especially for broad audience engagement. Tweet threads were posted on Twitter every Monday morning from 6 Apr. to 8 June 2020. Each thread consisted of 10 tweets. A hashtag #YardFruits was used to start the thread and for later reference. For the first nine threads only one fruit species was discussed per thread. The final thread consisted of single tweets of several species. Engagement percentage did not differ over time but did differ among the crop species. Tweets that did not include a photo received less engagement (2.7%) than those that did include a photo (4.7%). My Twitter account saw a 6.5% increase in followers during the series. Grape (Vitis sp.), passion fruit (Passiflora sp.), fig (Ficus carica), and pear (Pyrus communis) threads had the least engagement and were different from the Other Fruits thread. All other threads were similar. Extension educators can grow their influence by using well-targeted, focused tweets and tweet threads, especially those that use hashtags and photos.
Ricardo Goenaga, Angel Marrero, and Delvis Pérez
Dragon fruit (Hylocereus sp. and Selenicereus sp.), also referred to as pitahaya or pitaya, is a member of the Cactaceae family and native to the tropical forest regions of southern Mexico, Central America, and northern South America. Its fruit is becoming increasingly popular as consumers seek healthy and more diverse food products. The crop adapts to different ecological conditions ranging from very dry regions to wet ones receiving more than 3500 mm of rainfall per year. U.S. commercial production of dragon fruit occurs mainly in Florida, southern California, and Hawaii. As growers learn more about this crop and how productive it can be, the acreage planted is likely to increase. Twelve dragon fruit cultivars grown on an Oxisol soil were evaluated for 5 years under intensive management at Isabela, PR. There were significant differences in number and weight of fruit per hectare among years. Cultivars exhibited an increase in fruit number and yield from 2010 to 2013 and then leveled off or declined. There were significant differences among cultivars for number of fruit and yield per hectare. Cultivars N97-17 and N97-15 produced significantly more fruit averaging 74,908 fruit/ha. Significantly higher fruit yield was obtained by cultivars N97-17, N97-20, N97-22, and NOI-13 averaging 17,002 kg·ha−1. Cultivar Cosmic Charlie had the lowest fruit yield, averaging only 25.1 kg·ha−1. Individual fruit weight was significantly higher in cultivars N97-20 and NOI-13 with fruit weight averaging 346.3 g. Cultivars NOI-16, N97-18, and Cosmic Charlie had significantly higher fruit soluble solids than others, averaging 17.4%. Some of the cultivars used in this study have shown horticultural potential and may serve as new planting material for growers.
Subhankar Mandal and Christopher S. Cramer
Fusarium basal rot (FBR) of onion, which is caused by Fusarium oxysporum f.sp. cepae (Hanzawa) Snyder & Hansen (FOC) results in a substantial loss of marketable bulbs worldwide. One of the main reasons for the lack of FBR-resistant short-day cultivars is the unreliable screening methods available for the mature bulb stage when significant economic damage occurs. The objective of this study was to develop an artificial inoculation method with better quantification of inoculum for an effective selection of FBR-resistant mature onion bulbs. Mature bulbs of seven New Mexican short-day onion cultivars, along with susceptible and tolerant controls, were selected and evaluated for FBR resistance using mycelial and conidial inoculation methods, respectively. Transversely cut basal plates of mature bulbs were inoculated artificially with mycelia or conidia (12 × 105 spores/mL in 2014 and 3 × 105 spores/mL in 2015 embedded in potato dextrose agar plug) of a virulent FOC isolate ‘CSC-515’. Mature bulb evaluation using a visual rating scale (1 = no disease; 9 = >70% basal plate infected) revealed a high degree of FBR severity and incidence irrespective of the genetic background of the cultivars, minimizing the chance of disease escape, which is a significant problem in field inoculation. An attempt to inoculate intact basal plates postharvest resulted in minimal disease development, suggesting that mechanical resistance was conferred by the dry outer layer of the basal plate. The high selection pressure conferred by the conidial inoculation method developed in this study can effectively screen FBR-resistant onion bulbs to replace an unreliable field screening. Concentrations of the conidia lower than 3 × 105 spores/mL are recommended to detect subtle genetic differences in FBR resistance among the onion cultivars and their selected population.
Larissa Larocca de Souza and Marcelo L. Moretti
Hazelnut (Corylus avellana L.) basal sprouts, or suckers, are removed to train trees as a single trunk, facilitating mechanization. Suckers are routinely controlled with herbicides, often by using nozzles that generate fine droplets and spray volumes as high as 934 L·ha−1, making spray drift a concern. Spray nozzle type and carrier volume can impact herbicide efficacy and drift. Field studies compared the efficacy of 2,4-D and glufosinate in controlling suckers when applied with a flat-fan nozzle, producing fine droplets, to a TeeJet air-induction nozzle, producing ultra-coarse droplets. These nozzles were evaluated at 187 and 374 L·ha−1. Nozzle and carrier volume did not affect the efficacy of 2,4-D based on control, sucker height, or dry weight. The efficacy of glufosinate was unaffected by nozzle type or spray volume in most evaluations. These results indicate that hazelnut suckers can be effectively controlled using drift-reduction nozzles with lower carrier volumes (187 L·ha−1). Drift-reduction nozzles, coupled with lower spray volume, can maintain herbicide efficacy, minimize drift risk, and reduce cost.