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  • Author or Editor: Frank Louws x
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Grafting could potentially become an important part of integrated pest management programs in vegetable crops in the United States due to increased pathogen densities, reliance on pathogen susceptible varieties, increased use of organic and high tunnel production systems, limited land or input resources, value-added benefits, and the loss of, or regulatory restrictions on, soil fumigants. Adoption of this technology imposes additional costs on growers due to significantly higher grafted transplant prices, but associated yield improvements are potentially more than sufficient to offset the higher transplant costs. Therefore, the economic impact of the technology adoption depends highly on the specific circumstances of each grower. In this study, we propose a decision tool for growers to facilitate grafting technology adoption. We demonstrate an application of the proposed tool to a scenario based on real-life data for the open-field production of tomato (Solanum lycopersicum). The results show that based on a 30% loss in marketable yields due to disease pressure in nongrafted systems, yield improvements in the grafted system with resistant rootstock were sufficient to offset higher transplant and harvesting costs and resulted in higher net revenues. Net revenue estimates were $7126/acre in the nongrafted system and $8374/acre in the grafted system. The sensitivity analysis resulted in positive net revenues in the grafted system ranging from $108 to $12,328 per acre. Estimated marketable yield required in the grafted system to breakeven with the nongrafted system was 73,880 or 19,980 lb/acre more than marketable yield in the nongrafted system.

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Strawberry (Fragaria × ananassa) `Chandler' plants from three sources were grown in the annual hill plasticulture system during two growing seasons (1996-97 and 1997-98). These trials evaluated the yield and vegetative performance of bareroot plants from Prince Edward Island and Ontario, Canada, and plug plant tips that were rooted in North Carolina but obtained from Ontario Canada. At the end of the season, total and marketable yields and fruit weight were not different among the plant sources. In addition, plants from all three plant sources produced equivalent yields on a weekly basis. Monthly whole plant harvests revealed that plant source did not affect leaf area, root, crown, leaf, flower or fruit dry weight during most of the growing season. In addition, plant growth parameters (specific leaf area, leaf area ratio, leaf weight ratio, and root to shoot ratio) in general did not differ among plant source in any 1 month. Plant growth did show shifts in dry weight allocation and leaf area as the season progressed that were uniform among plant sources, with the majority of the growth occurring in the spring in the two months prior to harvest. This uniformity among plant sources will allow future research to emphasize plant production practices that may reduce the risk of pest and disease problems or optimize production practices favored by growers.

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At its most basic, grafting is the replacement of one root system with another containing more desirable traits. Grafting of tomato (Solanum lycopersicum) onto disease-resistant rootstocks is an increasingly popular alternative for managing economically damaging soilborne diseases. Although certain rootstocks have demonstrated ancillary benefits in the form of improved tolerance to edaphic abiotic stress, the mechanisms behind the enhanced stress tolerance are not well understood. Specific traits within root system morphology (RSM), in both field crops and vegetables, can improve growth in conditions under abiotic stress. A greenhouse study was conducted to compare the RSM of 17 commercially available tomato rootstocks and one commercial field cultivar (Florida-47). Plants were grown in containers filled with a mixture of clay-based soil conditioner and pool filter sand (2:1 v/v) and harvested at 2, 3, or 4 weeks after emergence. At harvest, roots were cleaned, scanned, and analyzed with an image analysis system. Data collected included total root length (TRL), average root diameter, specific root length (SRL), and relative diameter class. The main effect of cultivar was significant (P ≤ 0.05) for all response variables and the main effect of harvest date was only significant (P ≤ 0.01) for TRL. ‘RST-106’ rootstock had the longest TRL, whereas ‘Beaufort’ had the shortest. ‘BHN-1088’ had the thickest average root diameter, which was 32% thicker than the thinnest, observed in ‘Beaufort’. SRL in ‘Beaufort’ was 60% larger than ‘BHN-1088’. This study demonstrated that gross differences exist in RSM of tomato rootstocks and that, when grown in a solid porous medium, these differences can be determined using an image analysis system.

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Interest and use of grafted tomato (Solanum lycopersicum) in the United States continues to grow. Pioneered in Asia, herbaceous grafting is a commonly used cultural practice to manage many soilborne pathogens. Bacterial wilt (BW), caused by the pathogen Ralstonia solanacearum, is an aggressive soilborne pathogen that affects tomato grown in the southeastern United States. Traditional fumigation methods have limited effectiveness in the management of this pathogen. The present study was conducted to compare the bacterial wilt resistance of three commercially available tomato rootstocks, which are purported to be resistant to bacterial wilt: ‘Cheong Gang’, ‘RST-04-106-T’, and ‘Shield’. The determinate hybrid tomato ‘Red Mountain’, which is susceptible to bacterial wilt, was used as the scion and nongrafted control. Three locations were used over 2 years in North Carolina: an on-farm site with a history of bacterial wilt and two North Carolina Department of Agriculture Research Stations with no recent history of bacterial wilt. No disease symptoms were observed in any of the three grafted treatments, whereas the nongrafted controls showed between 30% and 80% disease incidence at the on-farm location. The resultant rootstock-imparted resistance improved marketable yields by between 88% and 125% compared with the nongrafted plants. When grown in locations lacking BW there were no yield benefits to grafting with any of the three rootstocks.

Open Access

In this study, we investigate the economic viability and environmental impact of three different soil management systems used for strawberry (Fragaria ×ananassa) production in the southeastern United States: 1) a conventional production system that is based on the current production practices implemented by growers, 2) a nonfumigated compost system with summer cover crop rotations and beneficial soil inoculants, and 3) an organic production system that includes practices approved for use under the National Organic Program (NOP). Under our assumptions, all three systems resulted in positive net returns estimated at $14,979, $11,100, and $19,394 per acre, respectively. The nonfumigated compost system and organic system also both resulted in considerable reductions in negative environmental and human health impacts measured by a set of selected indicators. For example, the total number of lethal doses (LD50) applied per acre from all chemicals used in each system and measuring acute human risk associated with each system declined from 118,000 doses/acre in the conventional system to 6649 doses/acre in the compost system and to 0 doses/acre in the organic system. Chronic human health risk, groundwater pollution risk, and fertilizer use declined as well in the compost and organic systems as compared with the conventional system.

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The following study was conducted to address water use efficiency in grafted tomato (Solanum lycopersicum) in an on-farm environment. The commercial rootstock cultivars Beaufort (BE) and Shield (S) were chosen as these two have different root system morphologies that may benefit water use efficiency. The heirloom cultivar Cherokee Purple (CP) was grafted onto both rootstocks and used as the nongrafted control. The study was conducted in 2016 and 2017 on a 5-acre vegetable and cut flower farm in North Carolina’s Piedmont region. Plants were grown under protected, high-tunnel culture where they received either 100% (3 hours every other day) or 50% (1.5 hours every other day) of the grower’s normal irrigation regime. At 50% irrigation, ‘Beaufort’-grafted plants yielded significantly more than nongrafted ‘Cherokee Purple’ and ‘Shield’-grafted plants. Furthermore, ‘Beaufort’-grafted plants at 50% irrigation yielded more than nongrafted ‘Cherokee Purple’ receiving the 100% irrigation treatment. The ‘Beaufort’-grafted plants significantly improved irrigation water use efficiency (iWUE) at the 50% irrigation treatment compared with the other graft treatments. Yield and iWUE of ‘Shield’-grafted plants were comparable with the nongrafted ‘Cherokee Purple’ at both irrigation treatments. Regardless of irrigation treatment, grafting onto ‘Beaufort’ improved the quality of total fruit harvested. An economic assessment was conducted to determine the feasibility of using grafted plants in conditions lacking significant disease pressure. Purchasing grafted transplants would increase the initial investment by $5227.2 per acre. However, the increased yield obtained when using ‘Beaufort’ rootstock at 50% irrigation increased net revenue by $35,900.41 per acre compared with nongrafted ‘Cherokee Purple’ receiving 100% irrigation, amounting to a 44.6% increase in net revenue while saving ≈383,242 gal/acre of water per growing season. These results indicate that growers can select rootstocks to better manage water use in an environmentally friendly manner without limiting economic gains.

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The grafting of herbaceous vegetables is an emerging development in the United States. This report provides an estimate of the variable costs of grafting within U.S. tomato (Solanum lycopersicum) transplant production systems. Grafted and nongrafted plants were propagated at two commercial farming operations in Ivanhoe, NC (NC) and Strasburg, PA (PA) and the farm in NC produced certified organic transplants. Detailed economic production sequences were generated for each site, and grafted and nongrafted transplant production costs were $0.59 and $0.13 in NC, and $1.25 and $0.51 in PA, respectively. Direct costs associated with grafting (e.g., grafting labor, clips, chamber, etc.) accounted for 37% to 38% of the added cost of grafting, and grafting labor was 11.1% to 14.4% of the cost of grafted transplant production. Seed costs represented 52% and 33% of the added cost of grafting at the two sites, and indirect costs (e.g., soil, trays, and heating) accounted for 10% and 30% of the added cost of grafting. Our findings suggest that under current seed prices and with similar production practices, the feasibility of grafting in the United States is not disproportionately affected by domestic labor costs. Additionally, the economic models presented in this report identify the cost of production at various transplant stages, and provide a valuable tool for growers interested in grafted tomato transplant production and utilization.

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In this study, we conducted an economic analysis of high tunnel and open-field production systems of heirloom tomato (Solanum lycopersicum) based on a two-year study at the Center for Environmental Farming Systems (CEFS) located in Goldsboro, eastern North Carolina. The research site was transitional organic using organically certified inputs and practices on land not yet certified. Production costs and returns were documented in each system and provide a useful decision tool for growers. Climatic conditions varied dramatically in 2007 compared with 2008 and differentially affected total and marketable yields in each system. Profits were higher in the open-field system and the high tunnels in 2007 and 2008, respectively. Sensitivity analysis was conducted using a range of market prices from $1.60/lb to $3.60/lb and a range of fruit marketability levels from 35% to 80%. Both systems were profitable except at the lowest price point and the lowest percent marketability level in high tunnel in 2007. At $2.60/lb, seasonal average sale price reported by growers for this region, and depending on percent marketability levels, the payback period for high tunnels ranged from two to five years. Presented sensitivity tables will enable decision makers to knowledgably estimate economic potential of open-field and high tunnel systems based on expected local prices and fruit quality parameters.

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Grafting watermelon (Citrullus lanatus) is a common practice in many parts of the world and has recently received increased interest in the United States. The present study was designed to evaluate early season growth, yield, and fruit quality of watermelon in response to grafting and in the absence of known disease pressure in a fumigated system. Field experiments were conducted using standard and mini watermelons (cv. Exclamation and Extazy, respectively) grafted onto 20 commercially available cucurbit rootstocks representing four species: giant pumpkin (Cucurbita maxima), summer squash (Cucurbita pepo), bottle gourd (Lagenaria siceraria), and interspecific hybrid squash [ISH (C. maxima × Cucurbita moschata)]. Nongrafted ‘Exclamation’ and ‘Extazy’ were included as controls. To determine early season growth, leaf area was measured at 1, 2, and 3 weeks after transplant (WAT). At 1 WAT, nongrafted ‘Exclamation’ produced the smallest leaf area; however, at 3 WAT, nongrafted ‘Exclamation’ produced the largest leaf area in 2015, and no differences were observed in 2016. Leaf area was very similar among rootstocks in the ‘Extazy’ study, with minimal differences observed. Marketable yield included fruit weighing ≥9 and ≥3 lb for ‘Exclamation’ and ‘Extazy’, respectively. In the ‘Exclamation’ study, highest marketable yields were observed in nongrafted ‘Exclamation’, and ‘Exclamation’ grafted to ‘Pelops’, ‘TZ148’, and ‘Coloso’, and lowest marketable yields were observed when using ‘Marvel’ and ‘Kazako’ rootstocks, which produced 47% and 32% of nongrafted ‘Exclamation’ yield, respectively. In the ‘Extazy’ study, the highest marketable yield was observed in nongrafted ‘Extazy’, and ‘Kazako’ produced the lowest yields (48% of nongrafted ‘Extazy’). Fruit quality was determined by measuring fruit acidity (pH), soluble solids concentration (SSC), lycopene content, and flesh firmness from a sample of two fruit from each plot from the initial two harvests of each year. Across both studies, rootstock had no effect on SSC or lycopene content. As reported in previous studies, flesh firmness was increased as a result of grafting, and nongrafted ‘Exclamation’ and ‘Extazy’ had the lowest flesh firmness among standard and mini watermelons, respectively. The present study evaluated two scions with a selection of 20 cucurbit rootstocks and observed no benefits in early season growth, yield, or phytonutrient content. Only three of 20 rootstocks in each study produced marketable yields similar to the nongrafted treatments, and no grafted treatment produced higher yields than nongrafted ‘Exclamation’ or ‘Extazy’. Because grafted seedlings have an associated increase in cost and do not produce increased yields, grafting in these optimized farming systems and using fumigated soils does not offer an advantage in the absence of soilborne pathogens or other stressors that interfere with watermelon production.

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Grafting of watermelon (Citrullus lanatus) is an established production practice that provides resistance to soilborne diseases or tolerance to abiotic stresses. Watermelon may be grafted on several cucurbit species (interspecific grafting); however, little research exists to describe root systems of these diverse rootstocks. A greenhouse study was conducted to compare root system morphology of nine commercially available cucurbit rootstocks, representing four species: pumpkin (Cucurbita maxima), squash (Cucurbita pepo), bottle gourd (Lagenaria siceraria), and an interspecific hybrid squash (C. maxima × C. moschata). Rootstocks were grafted with a triploid watermelon scion (‘Exclamation’), and root systems were compared with nongrafted (NG) and self-grafted (SG) ‘Exclamation’. Plants were harvested destructively at 1, 2, and 3 weeks after transplant (WAT), and data were collected on scion dry weight, total root length (TRL), average root diameter, root surface area, root:shoot dry-weight ratio, root diameter class proportions, and specific root length. For all response variables, the main effect of rootstock and rootstock species was significant (P < 0.05). The main effect of harvest was significant (P < 0.05) for all response variables, with the exception of TRL proportion in diameter class 2. ‘Ferro’ rootstock produced the largest TRL and root surface area, with observed values 122% and 120% greater than the smallest root system (‘Exclamation’ SG), respectively. Among rootstock species, pumpkin produced the largest TRL and root surface area, with observed values 100% and 82% greater than those of watermelon, respectively. These results demonstrate that substantial differences exist during the initial 3 WAT in root system morphology of rootstocks and rootstock species available for watermelon grafting and that morphologic differences of root systems can be characterized using image analysis.

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