Organic heirloom tomato production is limited in the southeastern United States by foliar and soilborne diseases, thermal stress, and weathered soil structure. Heirloom cultivars command a premium market, but tolerance to disease and abiotic stress is often poor. Organic growers need research that supports the advantages of market niches afforded by heirloom tomatoes through the development of integrated systems to manage pests and reduce risks of associated crop losses or low yields. Two major soilborne diseases common in the southeast, bacterial wilt (caused by Ralstonia solanacearum) and fusarium wilt (caused by Fusarium oxysporum f.sp. lycopersici), were effectively managed using susceptible heirloom scions grafted onto resistant rootstock. In naturally infested soil, bacterial wilt incidence for nongrafted ‘German Johnson’ was 79% and 75% in 2005 and 2006, respectively. ‘German Johnson’ showed no symptoms of bacterial wilt in either year when grafted onto the resistant genotypes CRA 66 or Hawaii 7996. Fusarium wilt incidence was 46% and 50%, respectively, in nongrafted and self-grafted ‘German Johnson’ controls. When ‘Maxifort’ rootstock was grafted with ‘German Johnson’, no symptoms of fusarium wilt were seen, and plants with ‘Robusta’ rootstock had an intermediate level of disease (29%). An evaluation of commercially available rootstock was carried out in three separate experiments in diverse organic production systems to determine yield impacts with low disease pressure. ‘Maxifort’ rootstock significantly increased yield in one location (P = 0.05), but ‘Maxifort’ and ‘Robusta’ rootstock did not consistently impact yield at the other two locations. Grafting is an effective management tool for organic growers in the southeast United States to reduce risk of crop loss resulting from soilborne diseases and will be a valuable component in an integrated pest management program.
Cary L. Rivard and Frank J. Louws
Sarah A. Masterson, Megan M. Kennelly, Rhonda R. Janke and Cary L. Rivard
The utilization of grafted tomato (Solanum lycopersicum) plants in the United States shows significant promise, particularly as intensively managed production systems like high tunnels and greenhouses become more popular. However, the availability of grafted plants in the United States is currently a major barrier and a large portion of farmers who would like to use grafted plants would prefer to propagate their own. The objectives of this study were to determine how healing chamber design affects graft survival and microclimate, and to investigate how scion leaf and shoot removal affects graft survival in various healing chambers. Similar experiments were repeated at two locations in Kansas and a split-plot, randomized complete block design (RCBD) was used in each, with three and four replications being conducted over time at each of the locations. Five chamber treatments were tested including a negative control (none) as well as shadecloth alone, white vinyl mesh, polyethylene film and shadecloth, and polyethylene film with shadecloth and a cool-mist humidifier. No statistically significant effects of chamber design were seen on grafted plant success. However, microclimate data from the various healing chambers offer valuable data toward determining the best management practices for grafted plants. Shadecloth alone showed significant promise as this covering provided cooler temperatures during the afternoon when the healing chambers were prone to excessive heat buildup. Three tube-grafting methods were tested, including standard tube-grafted plants (no leaves removed), leaf removal (LR) plants (≈75% of the leaf surface area was removed from the scion), and shoot removal (SR) plants (the apical meristem and all true leaves were removed). The SR method did not affect graft survival, but the LR method increased grafting success from 78% to 84% and was significant as compared with the other methods (P < 0.05). The long-term goals of this work are to develop successful propagation systems that can be used by small-acreage growers with limited greenhouse facilities. The data presented here indicate that high-humidity healing chambers (>85% relative humidity) may not be necessary for tomato, and LR can increase the grafting success rate.
Kelly Gude, Cary L. Rivard, Sara E. Gragg, Kimberly Oxley, Petros Xanthopoulos and Eleni D. Pliakoni
Specialty crop production in high tunnel systems has greatly expanded in the central United States. Strawberry (Fragaria ×ananassa) may be a viable high-value crop for high tunnel growers, but fall-planted production systems have a high opportunity cost in regard to winter production space. This study investigates the feasibility of spring-planted day-neutral strawberry cultivars in a high tunnel production system in Kansas. Furthermore, the goals of this report are to identify day-neutral cultivars that are successful in this production system and investigate the utility of evaporative cooling (EC), as they relate to fruit yield and marketability as well as incidence of gray mold (caused by Botrytis cinerea). High tunnel trials were conducted at the Kansas State University Olathe Horticulture Research and Extension Center during 2014 and 2015. Six commercially available cultivars were evaluated: Albion, Evie 2, Monterey, Portola, San Andreas, and Seascape in both years. Mature fruit (90% to 100% red) were harvested twice weekly for total and marketable (fruit with no defects) fruit yield. The results indicate that ‘Portola’ had the highest total fruit weight in both years at 0.60 and 0.51 kg/plant, respectively, and was significantly higher than ‘Monterey’, ‘Albion’, and ‘San Andreas’ in both years (P < 0.05). In 2014, ‘Portola’, ‘San Andreas’, and ‘Albion’ produced the largest total fruit average weight (grams/fruit) and were significantly larger than ‘Seascape’ and ‘Evie 2’ (P < 0.05). In 2015, ‘Portola’ had significantly larger fruit than all the other cultivars except San Andreas (P < 0.05). Marketability percent by weight ranged from 76.5% to 88.6% across both years and the highest marketability was observed with ‘Albion’ (89% and 83%) and ‘Monterey’ (85% and 84%) in 2014 and 2015, respectively. An examination of fruit production during the early, mid-, and late seasons was used to determine seasonal dynamics of each cultivar and the high tunnel system. The overall trend was that total fruit weight was highest during the midseason and total average fruit weight was largest in the early season. However, ‘San Andreas’ and ‘Seascape’ had similar levels of production between the early and midseason and had the lowest level of production in the midseason, particularly in the 2015 trial. In our trials, the use of EC did not affect fruit weight or gray mold incidence on strawberry fruit. Based on the crop productivity observed in our study, this production system has the potential to extend the season for strawberry growers in the central United States or provide a high-value rotational crop for existing high tunnel growers that does not require winter production space.
Zachary N. Hoppenstedt, Jason J. Griffin, Eleni D. Pliakoni and Cary L. Rivard
Sweetpotatoes (Ipomoea batatas) are nutritious, easily stored, and well adapted to a variety of organic farming operations. This widely consumed root crop is propagated through the use of cuttings, known as slips. Slips are commercially grown primarily in the southeastern United States, and growers in the central United States still have limited access to sweetpotato planting material. Production of organic slips in high tunnels (HTs) could be a profitable enterprise for growers in the central United States given the season extension afforded by controlled-environment agriculture, which could allow growers to diversify their operations and facilitate crop rotation. In trials conducted in 2016 and 2017 at two research stations in northeast and south central Kansas, a systems comparison was used to evaluate the yield and performance of organic sweetpotato slips grown in HT as compared with the open field (OF), with four to six replications at each location. Propagation beds planted with ‘Beauregard’ seed roots in 2016 and ‘Orleans’ in 2017 were established in HT and OF under similar cultural methods and planting schedules. Slips were harvested from both treatment groups and transplanted to field plots to investigate the impact of production system on transplant establishment and storage root production. Slip yield from HT was greater than OF at both locations in 2016 (P ≤ 0.001), but this trend was inconsistent in 2017. Slips grown in HT were on average 12% less compact (slip dry weight per centimeter length) with fewer nodes than their OF counterparts in 2016. Nonetheless, mean comparisons for vine length, stem diameter, and total marketable storage root yield were not significant between HT and OF treatments (1.7 and 2.1 lb/plant, respectively). Similarly, the number of marketable storage roots for HT and OF groups was comparable (3.4 and 3.8 storage roots/plant, respectively). Although more research is needed to evaluate the feasibility of slips grown in HT and to determine recommendations for seed root planting densities, results from this study suggest that HT organic sweetpotato slip production could be a viable alternative to OF production as it relates to slip performance. According to this study, HT production could be a useful mechanism for growing sweetpotato slips, which could provide regional growers more control over planting material. Furthermore, HT slip production could promote the adoption of an underused vegetable crop that can be grown throughout many parts of the United States.
Sarah A. Masterson, Megan M. Kennelly, Rhonda R. Janke and Cary L. Rivard
Grafting with interspecific hybrid rootstock is effective for tomato (Solanum lycopersicum) growers looking to reduce soilborne disease in the southeastern United States. However, production with grafted tomato has not been tested in the central United States, where soilborne disease pressure is low. Small-acreage growers would like to produce grafted plants themselves, but many have difficulty with propagation due to water stress in the scion postgrafting and/or high temperatures. Removing the upper portion of the scion to reduce leaf area during the grafting procedure [shoot removal (SR)] could help to reduce water stress postgrafting, but there are no data available that indicate what effect this practice has on tomato yield. Five high tunnel trials and one open-field trial were conducted in 2011 and 2012 to investigate potential yield effects related to the use of two rootstocks and SR during the grafting procedure. The implementation of grafting with rootstocks significantly increased fruit yield in five of the six trials (P < 0.05). The average yield increases by ‘Maxifort’ and ‘Trooper Lite’ tomato rootstocks were 53% and 51%, respectively, across all trials. SR during the grafting process may penalize tomato yield and our results suggest that rootstock vigor plays a role. Plants grafted with ‘Maxifort’ across all of the trials consistently increased shoot biomass in four of five of the high tunnel trials compared with nongrafted plants (P < 0.05), whereas plants grafted with ‘Trooper Lite’ rootstock increased shoot biomass in one trial. Similarly, the SR method penalized the total fruit yield of plants grafted with ‘Trooper Lite’ more often than those that were grafted with ‘Maxifort’. Our results suggest that plant growth and ultimately tomato fruit yield is affected negatively by using the SR grafting technique, particularly when less vigorous rootstock is used.
Cary L. Rivard, Olha Sydorovych, Suzanne O'Connell, Mary M. Peet and Frank J. Louws
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.
Olha Sydorovych, Cary L. Rivard, Suzanne O’Connell, Chris D. Harlow, Mary M. Peet and Frank J. Louws
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.