Optimal Storage Temperature and Duration of Edible Flowers
Edible flowers are usually sold in the refrigerated section of the produce department in grocery and specialty food stores. Researchers at Pennsylvania State University and Michigan State University acknowledged that temperature is usually the limiting environmental factor of fruit, vegetable and herb shelf life; however, with no previous research on edible flowers, they observed 5 species for cold storage shelf life and possible sensitivity to chilling injury.
Viola, pansy, borage, nasturtium and scarlet runner bean were harvested with fully expanded blooms. Experimental storage containers were 50- m thick, low-density polyethylene film bags, heat-sealed with four 0.4 mm holes to allow O2/CO2 gas exchange. Only flowers with no visible damage were used and the number of flowers placed in each bag was dependent on bloom size. Packages were placed in the dark at temperatures of 20, 10, 5, 2.5, 0, and –2.5 C (68, 50, 41, 36.5, 32, -36.5 F). Visual ratings on a 5-point scale were recorded daily for 14 days. A rating of 5 indicated no defects, while 1 indicated flower wilt, browning, or water soaking. Only flowers rated 3 to 5 were considered marketable.
Viola, pansy and nasturtium showed no visual quality loss after 2 weeks of storage at temperature 0 and 2.5 C (32 and 36.5 F). However, they remained marketable after 1 week of storage at temperatures between –2.5 and 10 C (-36.5 and 50 F). Borage flower quality declined rapidly as temperature increased. After 2 weeks, only borage flowers stored at –2.5 C (-36.5 F) were still marketable. The scarlet runner bean flowers were unmarketable at all temperatures after 2 weeks. On-plant flower longevity may be an indicator of storage life. In a 16 C (60.8 F) greenhouse, pansies, violas and nasturtium lasted 8 to 10 days, borage lasted 6 days and scarlet runner bean flowers lasted only 4 days.
The mean temperatures of refrigerated cases in grocery stores are 7.6 C (45.7 F) in winter and 8.4 C (47.1 F) in summer. Based on the observations in this study, all flowers except borage can be stored at these temperatures for 1 week without becoming unmarketable.
Kelley, K.M., A.C. Cameron, J.A. Beirnbaum and K.L. Poff. 2003. Effect of storage temperature on the quality of edible flowers. Postharvest Biology and Technology. 27, pp. 341-344.
Methyl Bromide Alternatives
With the eminent phaseout of methyl bromide by 2005, the United State Department of Agriculture—Agricultural Research Service is involved in a diversified research effort to develop alternative solutions for pre-plant management of soil-borne pests and pathogens. Since 1995 the research efforts have focused on strawberry, pepper, tomato, perennial and nursery cropping systems. However, recently the program was expanded to include ornamental and cut flower cropping systems.
The impending ban has scientists scrambling for alternative control methods. Methyl bromide can be used against a broad spectrum of soil pests and is effective on numerous soil types under a range of temperature and moisture conditions. So far, no other single control method offers the same flexibility and control seen in methyl bromide. If no broad-spectrum alternative can be found, greater field management will be necessary. First the grower will have to identify the problem in a given field and develop a control strategy that is 1) effective against the identified pest/pathogen, 2) effective under the field’s soil conditions, 3) economically feasible, and 4) environmentally acceptable. ARS also sees a need to educate growers so that they understand the pathogens and soil factors limiting crop production. The knowledge of biological, chemical and physical soil factors will allow them to develop a long-term, integrated approach including cultural, genetic, biological and chemical management strategies.
The level of pest and pathogen control seen with methyl bromide use on annual crop fields is often a cumulative result of years of fumigation. It is possible that unexpected pests and pathogens previously controlled—albeit unknowingly—by methyl bromide will appear. Because the ornamentals industry is composed of hundreds of species of crops and thousands of varieties, finding alternatives to methyl bromide is especially challenging. Phytotoxicity induced by alternative chemicals is a major concern due to the number of different crops grown concurrently and in succession.
Though the USDA is just beginning research in this area, they propose two alternatives that may be effective in floriculture production. First is the use of botanical extracts and essential oils to control Fusarium wilt. Studies have shown that soils infested with Fusarium oxysporum saw a significant reduction in pathogen population when treated with 10% solutions of clove extract, chili pepper extract and essential oil of mustard, and cassia. Obviously, this would be one aspect of an integrated management system.
Soil solarization has also shown potential as a methyl bromide alternative. Broadcast treatment was initially studied, but was determined to be incompatible with commercial production systems due to costs and accumulation of storm water runoff. Strip solarization on raised beds resulted in higher soil temperatures than broadcast solarization on a flat surface, eliminating the border effect and improving efficacy. The clear plastic used was painted white to terminate the solarization period and serve as a horticultural mulch. Pest control and marketable yield (of tomatoes) of solarized fields were comparable to that of methyl bromide treated fields. Weed control was also comparable except for the control of purslane and Texas panicum. Solarization did not control root-knot nematode unless combined with 1,3-dichloropropene + chloropicrin. Incidence of disease caused by Fusarium oxysporum, Phytophthora capsici and Sclerotium rolfsii were similar in solarized and methyl bromide treated fields.
In addition to research trials, the USDA is conducting large-scale field trials to identify technical problems, develop information on control effectiveness under a range of environmental and cultural practices and analyze costs incurred at the farm level. Applying soil solarization to large-scale trails identified several technical challenges that will need to be addressed. First, when using drip irrigation, the tube must be covered with soil to prevent melting during the solarization process. Also, paint coverage at solarization termination must be uniform and complete to prevent additional heating of the soil to temperatures dangerous to the transplants.
The Montreal Protocol and the US Clean Air Act call for a complete ban of methyl bromide by 2005, with only quarantine use exempt from the ban. The USDA-ARS is working to develop short term alternative technologies and long term solutions for more integrated, sustainable management systems among all agricultural commodities currently using methyl bromide.
Schneider, S.M., E.N. Rosskopt, J.G. Leesch, D.O. Chellemi, C.T. Bull and M. Mazzola. 2003. United States Department of Agriculture—Agricultural Research Service research on alternatives to methyl bromide: pre-plant and post-harvest. Pest Management Science. 59, pp. 814-826.
Prolonging Carnation Vase Life with Nitric Oxide
Postharvest application of silver thiosulphate (STS), 1-Methylcyclopropene (1-MCP) and nitric oxide (NO) has been shown to be effective in extending the postharvest life of a range of flowers, fruits and vegetables. With increasing environmental concerns over the use of silver (a heavy metal salt), 1-MCP and NO appear to be viable, competitive alternatives in the event that STS is banned from commercial application. There are however, limitations to the gaseous nature of 1-MCP and NO. Large scale fumigation requires certain infrastructure and some degree of technical operational expertise. These issues are prohibitive factors for efficient use in geographically isolated areas and developing countries. Researchers at the University of Newcastle, Australia, have conducted experiments to compare fumigant and in vivo delivery of NO on postharvest life of carnations.
Research in mammalian physiology has led to the emergence of NO donor technology. The NO is chemically stored in a solid compound and can be regenerated under the appropriate physical conditions. This study used the donor DETA/NO [2,2’-(hydroxynitrosohydrazino)-besethanamine] for in vivo release of NO by uptake of the compound in solution.
Partially opened flowers were cut to a stem length of 12 cm and placed in the appropriate treatment. Flowers were examined every 12 hours and rated 1 to 5 with 5 indicating fresh without any deterioration, 3 indicating moderate discoloration, mold growth or wilting, and 1 indicating entirely discolored, substantial mold growth and/or wilting. Postharvest life was determined to be time to reach a rating of 3.
The fumigation study looked at optimum concentration and duration. The optimum concentration to extend carnation postharvest life was 1-5 l/l. Compared to the air control, these concentrations resulted in a 30% increase in postharvest life. As duration increased from 0.5 to 2 hours, postharvest life linearly decreased. At the optimum concentration, the 0.5-hour exposure resulted in the longest postharvest life.
The in vivo study found that flower stems stored in DETA/NO solution of 10-100 mg/l produced a 50% extension in postharvest life compared to the control held in water. At 1000 mg/l DETA/NO, the flower petals began browning on the edge suggesting phytotoxicity.
The results of this study suggest the use of NO as an effective postharvest treatment. As a fumigant application, NO requires less exposure time than 1-MCP allowing for greater product movement through a commercial operation. The drawbacks include a need for gas cylinders and regulators that would increase cost and the use of sealed chambers—not always amenable to field operations—for fumigant application. The donor technology utilized by DETA/NO has proven effective at prolonging postharvest life of carnations. Further work is needed to observe its effectiveness on other species; however, as a solid that dissolves in water, the technology might be easily integrated into current handling systems.
Bowyer, M.C., R.B.H. Wills, D. Badiyan, and V.V.V. Ku. 2003. Extending the postharvest life of carnations with nitric oxide—comparison of fumigation and in vivo delivery. Postharvest Biology and Technology. 30, pp. 281-286.