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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Research Project #439337

Research Project: Methyl Bromide Alternative Treatments for Perishable and Stored Products

Location: Crop Improvement and Protection Research

2021 Annual Report

The long-term objective of this project is the development of alternative postharvest treatments that are safe and effective for control of pests and microbes on fresh and stored products. This project builds upon our recent progress in developing nitric oxide (NO) fumigation treatments for control of pests and pathogens, and sulfur dioxide fumigation treatments for control of postharvest pests. Specifically, during the next five years we will focus on the following objective. Objective 1: Determine the effectiveness of nitric oxide and sulfur dioxide fumigation for postharvest control of pests and pathogens and evaluate the effectiveness of essential oils as alternative fumigants for postharvest pest control. Sub-objective 1A: Determine effectiveness of nitric oxide fumigation for control of microbes (pathogens) on stored products. Sub-objective 1B: Evaluate nitric oxide fumigation for control of insects and microbes (pathogens) in large-scale fumigation. Sub-objective 1C: Determine effective sulfur dioxide fumigation treatments against pests on fresh and stored products. Sub-objective 1D: Determine effective fumigation treatments with plant essential oils against postharvest pests.

Sub-objective 1A: Almonds, peanuts, and corn will be fumigated with nitrogen dioxide (NO2) in separate studies to determine microbial loads and effective treatments to control bacteria and fungi. Each product will also be disinfected with NO2 fumigation to kill bacteria and fungi and, then, artificially inoculated with spores of non-aflatoxin producing strain of Aspergillus flavus. Inoculated products will then be cultured and fumigated with NO2 to verify effective control of A. flavus. Sub-objective 1B: Large scale fumigation tests with NO + NO2 will be conducted in a 246 cm tall mini silo filled with corn to evaluate fumigant penetration and efficacy against rice weevil and Aspergillus flavus fungus. Rice weevil adults and A. flavus infected corn will be positioned at different depths in corn in the mini silo. An air pump will be used to circulate air in the mini silo. After injecting NO under specific ultralow oxygen conditions to have expected NO level for insect control and NO2 level for microbial control, NO and NO2 will be monitored at different heights of the mini silo. Efficacy against rice weevil and A. flavus will be evaluated at the end of fumigation treatment. Fumigations will be conducted with different combinations of NO and NO2 concentrations and treatment times to determine effective NO+NO2 fumigation for control rice weevil and the fungus. NO and NO2 levels will also be measured without air circulation to determine fumigant penetration in the mini silo. Sub-objective 1C: Small-scale SO2 fumigation tests will be conducted to determine effective combinations of SO2 concentrations and treatment times at different temperatures for control of rice weevil, confused flour beetle, naval orangeworm, and Pacific spider mite. Different life stages of insects/mites will be fumigated to determine the most tolerant life stages and effective treatments will be developed to control the most tolerant life stage for each pest. Once an effective treatment is identified, large-scale SO2 fumigation treatments will be conducted to control each pest on a selected product. Rice weevil, confused flour beetle, naval orangeworm, and Pacific spider mites will be fumigated together with corn, wheat, pistachio, and table grape, respectively, in large-scale SO2 fumigation treatments. The large-scale SO2 fumigation for controlling rice weevil will be conducted in the mini silo. Large-scale SO2 fumigation against other pests on respective products will be conducted in 26 l chambers modified from 7 gal plastic buckets. Sub-objective 1D: Rice weevil, navel orangeworm, and western flower thrips will be fumigated with plant essential oils (PEO) including anisole and methyl benzoate in glass jars. The pests at different life stages will be exposed to PEO at different doses for different durations at different temperatures to determine effective treatments. For each insect species, once an effective treatment is identified, it will be tested in larger scale fumigation tests with products to verify efficacy. For western flower thrips, effects of PEO fumigation on apple quality will also be evaluated in large-scale fumigation tests.

Progress Report
This report documents progress for project 2038-22430-003-00D, which started in October 2020 and continues research from project 2038-22430-002-00D, "Methyl Bromide Replacement: Post-harvest Treatment of Perishable Commodities." Research was initiated on sulfur dioxide (SO2) fumigation for control of insects in stored products rice weevil and confused flour beetle adults were fumigated with SO2 at different concentrations for 24 hours at temperatures of 5, 15, and 25°C to determine effective treatments and influence of temperature. Preliminary results showed effective control of both species with SO2 at 0.2% concentration. Research on SO2 fumigation for control of navel orangeworm was also initiated. Preliminary tests showed that navel orangeworm eggs were susceptible to SO2 fumigation and complete control of eggs can be achieved in 24 hour fumigation with 0.1% SO2. These studies are directly related to Sub-objective 1C. Additional research was conducted to evaluate effects of long-term storage under controlled atmosphere with low oxygen on development and survival of rice weevil and confused four beetle and the research is still in progress. Preliminary results showed that 45-day storage under low oxygen atmospheres had significant effects on success of development from eggs to adults or later stages and storage under 5% oxygen completely controlled eggs of both insects.

1. Effects of nitrogen dioxide (NO2) fumigation in controlling microbes on unshelled peanuts. Stored products, such as peanuts, face both pest infestation and microbial infection. ARS researchers in Salinas, California, conducted research to expand the fumigant nitric oxide (NO) to control both pests and microbes. Nitric oxide is a newly discovered fumigant for postharvest pest control under ultralow oxygen environment. Nitric oxide fumigation contains nitrogen dioxide, which is a strong antimicrobial agent. In this laboratory study, unshelled peanuts were fumigated with 0.3%, 1.0%, and 3.0% nitrogen dioxide (NO2) for three days at 25°C and microbial loads inside and outside unshelled peanuts were determined. All treatments had significant effects on microbial loads and 100% reduction was achieved for the 1.0% and 3.0% NO2 fumigation treatments. The results suggest that NO fumigation with desired levels of NO and NO2 has potential to control both pests and microbes on unshelled peanuts and will benefit peanut producers and processors.

2. Efficacy of essential oil anisole as a potential fumigant for postharvest pest control. There is a need for environmentally friendly fumigants for postharvest pest control. The plant essential oil, anisole, is insecticidal and has potential as an alternative fumigant due to its smaller molecular size and higher vapor pressure than most other plant essential oils. ARS researchers in Salinas, California, conducted research to evaluate anisole as a potential fumigant for postharvest pest control and tested anisole against four insects. Anisole fumigation was effective against adults of three stored product insects including rice weevil, granary weevil, and confused flour beetle; as well as against larvae and adults of western flower thrips. Complete control of all insect species was achieved in four to 24 hours depending on anisole dose and insect species. These results indicate that anisole has potential as a fumigant for postharvest pest control, which will benefit the fresh and stored product industries.

3. Efficacy of nitric oxide fumigation against different life stages of light brown apple moth. Light brown apple moth has established in California since its earlier detection over 10 years ago. Because this pest has a very broad host range, very limited distribution, and is quarantined in most countries, effective quarantine treatments are needed. ARS researchers in Salinas, California, conducted research to determine the effectiveness of their recently discovered fumigant, nitric oxide (NO), against this pest. Fumigations with NO at different concentrations for different treatment durations at a low temperature of 2°C were conducted against different life stages of light brown apple moth. Complete control of larvae and pupae was achieved in eight-hour fumigation with 2.0% NO and eggs were successfully controlled in six, 12, and 24 hour fumigations with 5.0, 3.0, and 2.0% NO respectively. These results indicate that nitric oxide can be suitable for postharvest control of light brown apple moth and, therefore, has potential to facilitate export of fresh fruit and vegetables.

Review Publications
Oh, S., Singh, R., Liu, Y.-B. 2020. Nitrogen dioxide fumigation for microbial control on unshelled peanuts. Agricultural Sciences. 11(12):1159-1169.
Yang, X., Liu, Y.-B., Simmons, G., Light, D.M., Haff, R.P. 2020. Nitric oxide fumigation for control of navel orangeworm, Amyelois transitella, on walnut. Journal of Applied Entomology. 145(3):270-276.
Yang, X., Liu, Y.-B. 2021. Anisole is an environmentally friendly fumigant for postharvest pest control. Journal of Stored Products Research. 93. Article 101842.