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Charles E. Barrett, Xin Zhao and Robert McSorley

Organic heirloom tomatoes (Solanum lycopersicum L.) are difficult to grow in Florida as a result of root-knot nematodes (Meloidogyne spp.) (RKN) and hot, humid growing conditions. Although grafting with resistant rootstocks has been shown effective for RKN management in tomato production, little research has been conducted on grafted heirloom tomatoes under Florida conditions. In this 2-year study, two susceptible heirloom tomato scions, ‘Brandywine’ and ‘Flamme’, were grafted onto two hybrid rootstocks, i.e., interspecific tomato hybrid rootstock ‘Multifort’ (S. lycopersicum × S. habrochaites) and tomato hybrid rootstock ‘Survivor’ (S. lycopersicum). Non-grafted and self-grafted scions were used as controls. Three field trials were conducted including the 2010 and 2011 organic field trials as well as a transitional organic field trial in 2011. There was a lack of RKN pressure in the organic field in 2010. In 2011, the RKN population was higher in the transitional field than the organic field, whereas grafting with hybrid rootstocks significantly reduced root galling (P ≤ 0.0001) in both fields. In the organic field, the hybrid rootstocks performed similarly and significantly reduced root galling compared with the non-grafted and self-grafted scions by ≈80.8%. In the transitional field, compared with non-grafted scions, the root galling reduction by ‘Survivor’ (97.1%) was significantly greater than that by ‘Multifort’ (57.6%). In general, tomato plants grafted onto ‘Multifort’ tended to be more vigorous than all other treatments. There was no clear relationship between root galling and tomato yields. Grafting did not significantly affect the total marketable yield for the scion ‘Flamme’ in both years. Total marketable yield was similar among treatments in 2010 but varied in 2011 for the scion ‘Brandywine’. In 2011, the non-grafted ‘Brandywine’ and ‘Brandywine’ grafted to ‘Survivor’ produced significantly higher (P < 0.05) yields than other treatments in the organic field. However, in the transitional field, ‘Brandywine’ grafted to ‘Multifort’ resulted in significantly higher (P < 0.05) yields than the non- and self-grafted ‘Brandywine’ treatments. Grafting with appropriate rootstocks may play an effective role in RKN management during the transition to organic production when high populations of nematodes are present.

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Charles E. Barrett, Xin Zhao and Alan W. Hodges

Growers are looking for sustainable alternatives to methyl bromide as a soil fumigant that are effective and economical. Increased demand for organically produced fruits and vegetables has also contributed to the need for environmentally friendly soil-borne disease control methods. Grafting may be a valuable tool for vegetable growers to cope with pest management challenges in production of cucurbits and solanaceous crops; however, there are concerns regarding the higher costs associated with the use of grafted plants in the United States. The main objective of this 2-year study was to determine if grafting with a resistant rootstock could be cost-effective to overcome root-knot nematodes (RKN) (Meloidogyne sp.) and maintain fruit yield in organic heirloom tomato (Solanum lycopersicum) production in Florida's sandy soils. The heirloom tomato cultivar Brandywine was grafted onto the rootstock ‘Multifort’. Nongrafted and grafted ‘Brandywine’ plants were grown organically in two fields that exhibited different levels of RKN infestations. Grafted and nongrafted transplants were estimated to cost $0.78 and $0.17 per plant, respectively. The cost of rootstock seeds accounted for 36% ($0.28/plant) of the total cost of the grafted transplants and 46% of the cost difference between grafted and nongrafted plants. Sensitivity analyses were conducted using these estimated transplant production costs and crop yield data from the field trials as well as price information for heirloom tomato. Results showed that under severe RKN pressure, grafting may be an economically feasible pest control measure to help maintain a profitable production given that the risk of economic crop losses due to RKN outweighed the higher cost of grafted transplants.

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Charles E. Barrett, Xin Zhao, Charles A. Sims, Jeffrey K. Brecht, Eric Q. Dreyer and Zhifeng Gao

Grafting has many purposes in vegetable production. It is used for control of soilborne pathogens, season extension in protected culture, and improving productivity in cucurbitaceous and solanaceous crops. Consumers desire heirloom tomatoes (Solanum lycopersicum) for their perceived excellent flavor. Heirloom tomatoes are susceptible to many soilborne diseases and may benefit from grafting onto more robust, disease-resistant rootstocks especially under organic production. In this two-year study, heirloom tomato ‘Brandywine’ was grafted onto tomato hybrid ‘Survivor’ and interspecific tomato hybrid ‘Multifort’ rootstocks to determine the effects of grafting on fruit quality attributes such as soluble solids content (SSC), pH, total titratable acidity (TTA), and vitamin C. Nongrafted and self-grafted ‘Brandywine’ tomatoes were included as controls. Consumer sensory tests were also conducted to assess the effects of grafting on overall appearance and acceptability, firmness, tomato flavor, and sweetness. No significant differences in vitamin C, SSC, pH, or TTA were found in fruit from the nongrafted, self-grafted, and ‘Brandywine’ grafted with the two rootstocks either year. The SSC of all tomatoes in 2010 was lower than that of 2011. In 2010, fruit from ‘Brandywine’ grafted onto the rootstock ‘Survivor’ was scored significantly lower in appearance, acceptability, and flavor than the nongrafted ‘Brandywine’ treatment. All grafted treatments resulted in a significant decrease in acceptability ratings in the consumer sensory test. No significant differences were observed between nongrafted and grafted treatments in 2011. Consumers who reported more frequent consumption of fresh tomato tended to give lower ratings for most sensory attributes evaluated. Harvest time and fruit ripeness need to be considered in future research to better understand the influence of grafting with selected rootstocks on fruit composition and sensory attributes of heirloom tomatoes.

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Fernanda Souza Krupek, Christian T. Christensen, Charles E. Barrett and Lincoln Zotarelli

The cost of seed accounts for nearly 10% of the estimated production cost of chipping potato (Solanum tuberosum) production in Florida. Optimizing seed piece spacing can reduce costs without affecting potato yield. This study evaluated the effects of seed piece spacing on yield, quality, and economic revenue of chipping potato production in north Florida. A field experiment was conduct during the spring of 2013, 2014, and 2016 in Hastings, FL, with a split-plot randomized complete block design. In-row seed piece spacings of 10, 15, 20 (industry standard), 25, and 30 cm were assigned as the main plot and S. tuberosum potato cultivars (Atlantic, Harley Blackwell, and Elkton) as the subplots. Marketable tuber yield ranged between 10.8 and 15.2 Mg·ha−1 in 2013, 10.1 and 12.8 Mg·ha−1 in 2014, and 9.9 and 19.7 Mg·ha−1 in 2016. Overall lower yields in 2013 were due to three freeze events early in the season. Widening seed piece spacing resulted in a linear decrease in total and marketable yield in 2013 and 2014. Conversely, seed piece spacings of 10 and 15 cm showed lower marketable yields in 2016. There was no interaction between in-row spacing and cultivar in any year tested. Cultivars performed variably across years for total and marketable yield and specific gravity. Tuber specific gravity was unaffected by seed piece spacing, except in 2013, when 25 and 30 cm resulted in slightly higher values. There was no significant difference in total and marketable yield between the industry standard seed piece spacing 20 and 25 cm in any year. In-row spacing of 25 cm in 2013 and 30 cm seed piece spacing in 2014 and 2016 provided the greatest economic return. Net revenue can be increased by adjusting the in-row seed piece spacing from the commercial standard of 20 to 25 cm, which reduces production cost without negatively impacting yields.

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Trinidad Reyes, Terril A. Nell, James E. Barrett and Charles A. Conover

This experiment was conducted to evaluate the interior performance of Chrysalidocarpus lutescens grown for 8 months under 481, 820, and 1241 μmol·m–2·s–1 and fertilized weekly with a 20N–4.7P–16.6K soluble fertilizer at 440, 880, and 1660 mg/pot. Afterwards, plants were placed indoors and maintained at 20 μmol·m–2·s–1 for 12 h daily at 21±1C and a relative humidity of 50%±5% for 3 months. At the end of the production phase, light compensation point (LCP) varied from 243 μmol·m–2·s–1 at the high irradiance level to 140 μmol·m–2·s–1 at the lowest one. Chlorophyll concentration in the leaves was not affected by irradiance or fertilizer rate. Starch concentration in stems and roots were higher the lower the fertilizer rate applied during production and the higher the irradiance level. After 3 months indoors, LCP declined for all the treatments, but the lowest LCP reached, 126 μmol·m–2·s–1, was still too high if the plant has to survive an interior environment. After the interior holding period, a 45% to 55% reduction was observed on leaf, stem, and root soluble sugar concentrations, and stem and root starch concentrations decreased by 97%, and 62% to 72%, respectively, compared to the concentration at the end of production. The number of fronds increased in all treatments during the postproduction evaluation. However, the drastic carbohydrate concentration depletion during the interior holding period indicates that C. lutescens is not a species for extended use under very low interior light conditions.

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Trinidad Reyes, Terril A. Nell, Charles A. Conover and James E. Barrett

Effects of three light intensities (564, 306 and 162 μmol m-2 s-1) and three fertilizer rates (220, 440 and 880 mg/15 cm pot, weekly) were evaluated on acclimatization potential of Chamaedorea elegans. Treatments were applied during four months under greenhouse conditions after which plants were placed indoors (20 μmol m-2 s-1, 21±2C and 50% RH) for two months. Light compensation point (LCP) was significantly reduced by decreasing light intensity and increasing fertilizer rates. Leaf and root fresh and dry weights increased with irradiance while shoots were not affected. Chlorophyll a levels were higher in plants grown under the lowest light intensity. Carbohydrate content is being analyzed and anatomical examination of leaves studied. Plant performance indoors will be discussed. These studies demonstrate that Chamaedorea, a monocot, acclimatizes similarly to dicots.

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Trinidad Reyes, Terril A. Nell, James E. Barrett and Charles A. Conover

The effect of irradiance and fertilizer level on the acclimatization of Chamaedorea elegans Mart. was studied. Chamaedorea elegans was grown for 4 months in 1.6-liter pots under 162, 306, or 564 μmol·m–2·s–1 and fertilized weekly with 20N–4.7P–16.6K soluble fertilizer at 220, 440, or 880 mg/pot. At the end of the production period, plants were moved to interior rooms and maintained for 2 months at 20 μmol·m–2·s–1 for 12 h daily at 21 ± 1C and a relative humidity of 50% ± 5%. At the end of the production phase, the light compensation point (LCP) and the concentration of nonstructural carbohydrates were lower, and chlorophyll concentration was higher the lower the irradiance level. Increasing fertilizer concentration decreased the number of fronds, LCP, and nonstructural carbohydrates. After 2 months in the interior environment, LCP and number of fronds of C. elegans did not differ among treatments. Chlorophyll concentration of plants grown under 564 μmol·m–2·s–1 had increased 61%, while starch in the stem had decreased 43% relative to the concentration found at the end of the production period. In C. elegans grown under 306 μmol·m–2·s–1, stem starch depletion was only 13% during the interior evaluation period. These results indicated that C. elegans grown under the highest irradiance level used reserved carbohydrates in the interior environment while adjusting to low light and producing new leaves. Chamaedorea elegans was best acclimatized at the intermediate irradiance and medium fertilizer concentration.

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Charles E. Barrett, Lincoln Zotarelli, Lucas G. Paranhos, Peter Dittmar, Clyde W. Fraisse and John VanSickle

Weather has a major influence on cabbage (Brassica oleracea var. capitata L.) production. Variation in yield between years and cropping seasons is common in North America. Cabbage in Florida has historically been cultivated on bare ground with seepage irrigation. The objectives of this study were to compare yield and profit of a bare ground cabbage production system used in Florida with an alternative plasticulture system. Data from various cabbage trials were combined by production system and used to create regression equations that predicted yield based on air temperature and solar radiation that were significantly correlated with yield. The regression equations were then simulated with correlated stochastic air temperature and solar radiation to estimate the yield distributions for both systems. Cabbage price ($/Mg fresh) was stochastically simulated (correlated to yield) to be used in the profit model. The profit model was created by using the product of yield and the price per unit yield minus fixed and variable costs associated with production and marketing. Simulated profit for bare ground and plasticulture was used to estimate their respective distributions to provide a tool for making better management decisions in the presence of risky weather conditions. The plasticulture system was estimated to have a 36% higher cost but a 57% higher profit than the bare ground system. This is, in large part, because the simulated mean yield for the bare ground system was 29.7 Mg·ha−1 compared with 54.4 Mg·ha−1 for plasticulture. These findings confirmed that plasticulture is an economically viable best management practice for cabbage production in Northeast Florida.

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Lucas G. Paranhos, Charles E. Barrett, Lincoln Zotarelli, Tatiana Borisova, Rebecca Darnell and Kati Migliaccio

Seepage is characterized as an inefficient irrigation method with regard to water and nutrient use. There is a need for an economically viable irrigation alternative to seepage, which increases crop productivity and profitability in Florida. The use of plastic mulch and drip irrigation for cabbage (Brassica oleracea var. capitata) production increases plant population per area and reduces the irrigation water requirement. However, plasticulture has a high capital investment and operating cost. The objectives of this study were to compare the profitability of plasticulture cabbage production and traditional seepage bare ground irrigation systems for Florida cabbage production, and to determine the breakeven point for cabbage grown under plasticulture given a range of market prices. The preharvest cost per acre for the plasticulture system was significantly higher than the cost for the seepage system ($4726 and $3035 per acre, respectively). However, for all planting dates considered in this study, the plasticulture system resulted in a significant increase in marketable yields when compared with the seepage system. The resulting increase in potential revenue offset the increase in preharvest costs and assured a positive net return on investment over the whole range market prices. It was also observed that low air temperatures combined with reduced solar radiation can prevent optimum plant development for cabbage transplanted between November and mid-December. Therefore, the return on investment may be reduced during less favorable climatic conditions for cabbage growth, making the plasticulture system less economically desirable for certain planting dates.

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Charles E. Barrett, Lincoln Zotarelli, Lucas G. Paranhos, Brian S. Taylor, Peter Dittmar, Clyde W. Fraisse and John VanSickle

Florida is a major fresh-market cabbage (Brassica oleracea L. var. capitata) producing state in the United States. The current cabbage production system relies on bare ground and subirrigation that requires a large volume of water to irrigate the crop. The bare ground system facilitates a maximum of 48,438 plant/ha, while there is a potential to increase plant population per area using plasticulture and drip irrigation. The objectives of this study were to determine the optimum cabbage plant population and plant arrangement that maximizes marketable yield per area for a high cabbage population plasticulture system. Cabbage was grown on 1.2-m-wide raised beds with black plastic mulch and drip irrigation. Plants were grown in either three or four rows with in-row plant spacings ranging from 15 to 35 cm and plant populations ranging from 41,518 to 129,167 plants/ha. Cabbage marketable yield increased as in-row spacing increased. Yields ranged from 19.7 to 69.7 Mg·ha−1. Marketable yield was not different between 3 and 4 rows for in-row spacings above 25 cm. The 15 and 20 cm in-row spacing produced significantly lower yields in the 4-row configuration as compared with the 3-row configuration in Fall and Winter 2011. Wider in-row spacings produced a greater percentage of heads of marketable size while reducing the percentage of small heads when compared with narrower in-row spacings. Mean head weight increased as in-row spacing increased and a 3- or 4-row configuration with an in-row spacing between 25 and 30 cm had consistently high yields in all three seasons compared with narrower in-row plant spacings. These results indicated that with a high population plasticulture system variable plant populations could be selected. In-row plant spacings between 30 and 35 cm may be beneficial for early plantings while a 25-cm spacing could be more productive for later plantings, especially when weather conditions are favorable.