Location: Crop Improvement and Protection Research
2024 Annual Report
Objectives
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.
Approach
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 2038-22430-003-000D, titled, “Methyl Bromide Alternative Treatments for Perishable and Stored Products”, which started in October 2020.
In support of Sub-objective 1C, ARS researchers in Salinas, California, conducted research on sulfur dioxide (SO2) fumigation for control of spotted wing drosophila (SWD) on blueberries and this research is continuing. SWD flies were very susceptible to SO2 fumigation and 30-minute fumigations with 0.2% SO2 achieved 100% mortality of adult fruit flies. However, 3 h fumigations with 2% SO2 were needed to achieve >95% mortality for eggs and larvae in infested blueberries. The treatments with high levels of SO2 resulted in discoloration of blueberries.
The following progress was also achieved on Sub-objective 1D. ARS scientists in Salinas, California, continued to evaluate new alternative fumigants for postharvest pest control. Chlorobenzene was identified to be an effective fumigant and its efficacy was demonstrated against six insect species including confused flour beetle, rice weevil, navel orangeworm, western flower thrips, spotted wing drosophila, and eastern subterranean termite works. Complete control of western flower thrips with fresh fruit was achieved in 3 h fumigation at 5 degrees C. Evaluation of its effects on postharvest quality of fresh produce is in progress. The discovery of chlorobenzene has been approved for U.S. patent application.
As well, preliminary research was conducted by ARS scientists in Salinas, California, to evaluate potential of ultralow oxygen (ULO) atmosphere treatment for control of spotted wing drosophila in blueberries and cherries. Positive results have been achieved and the research will continue in FY25.
Research was also conducted by ARS scientists in Salinas, California, on control of Verticillium pathogen in spinach seeds using sulfur dioxide fumigation in collaboration with another ARS scientist at Salinas, California.
Accomplishments
1. Sulfur dioxide fumigation for control of confused flour beetle and rice weevil. Confused flour beetle and rice weevil are two major stored product insects. ARS researchers in Salinas, California, evaluated sulfur dioxide (SO2) fumigation as an alternative treatment to control two insects. All life stages of confused flour beetle and rice weevil were treated in SO2 fumigations. Effective control of all life stages of both species was achieved in 3-h SO2 fumigation treatments. Confused flour beetle was more susceptible to SO2 fumigation than rice weevil, and complete control of adults and all life stages of confused flour beetle were achieved in 3-h fumigations with 0.5 and 2.0% SO2, respectively. For rice weevil, 3-h fumigations with 1.5% SO2 resulted in 96.5% adult mortality, and the fumigation with 2.0% SO2 resulted in 99.27% mortality of adults and 87.5% mortality of immature stages. Three-hour fumigations with 1% SO2 resulted in less than 5% egg survival to adults. The study demonstrated high efficacy of SO2 fumigation against the insects and suggested that SO2 fumigation has good potential for postharvest pest control on stored products.
2. Effects of sulfur dioxide fumigation on mortality of western flower thrips and postharvest quality of select fresh produce. Although sulfur dioxide (SO2) has a long history of being used in pest control, it is rarely used to control postharvest pests presently and there is also a lack of studies of SO2 fumigation for postharvest pest control. In this study, ARS researchers in Salinas, California, evaluated SO2 fumigation for efficacy against western flower thrips (Frankliniella occidentalis) and phytotoxicity to four select fresh fruits and vegetables and found the process to be very effective against western flower thrips. Fumigations with 0.3 and 0.5% SO2 for 60 and 30 minutes respectively at a low temperature of 5 degrees C achieved 100% thrips mortality. Broccoli, bell peppers, apples, and navel oranges along with thrips were also subjected to 30-minute fumigations with 0.3-0.5% SO2 to verify efficacy and determine potential phytotoxicity. The fumigation resulted in complete control of thrips and no negative impact on postharvest visual quality of bell peppers and oranges. However, fumigation did cause severe discoloration of broccoli and minor impact as darkened lenticels on apples. The results of the study suggest that SO2 fumigation has excellent potential to be used safely and effectively against sensitive pests on select fresh fruit and vegetables including peppers and citrus fruits.
3. Evaluation of fumigant toxicity of cyclohexanone to five species of insect pests. Cyclohexanone is a major precursor for nylon production and is also used as a pesticide solvent. In this study, ARS researchers in Salinas, California, evaluated cyclohexanone as a fumigant against rice weevil adults, confused flour beetle adults, western flower thrips larvae and adults, spotted wing drosophila adults, and subterranean termite workers. Cyclohexanone fumigation was found to be effective against all five insects. Complete control of spotted wing drosophila adults and eastern subterranean termite workers was achieved in 1 and 3 h respectively. Stored product insects confused flour beetle and rice weevil adults were more tolerant to cyclohexanone fumigation. Fumigations of 24 h caused 100% mortality of rice weevil adults and 98% mortality of confused flower beetle adults. At 5 degrees C, complete control of western flower thrips was achieved in 3 and 6 h fumigations depending on doses of cyclohexanone. The results of effective control of all five insect species suggest that cyclohexanone has the potential to be used as a fumigant for postharvest pest control.
4. Streptomyces bacteria produce compounds that inhibit soilborne plant pathogens of lettuce and strawberry. Soilborne fusarium wilt diseases caused by the fungus Fusarium oxysporum are a major problem in strawberry and lettuce production. Use of microbial biological control agents is a potential approach for management of fusarium wilt of lettuce and strawberry. In this research, ARS scientists in Salinas, California, showed Streptomyces bacteria from soil produce unidentified compounds that significantly suppress the growth of F. oxysporum. This research suggests Streptomyces bacteria or the antifungal compounds they produce can be used to reduce fusarium wilt of lettuce and strawberry.
Review Publications
LeBlanc, N.R., Harrigian, F.C. 2024. Green waste compost impacts microbial functions related to carbohydrate use and active dispersal in plant pathogen-infested soil. Microbial Ecology. 87. Article 44. https://doi.org/10.1007/s00248-024-02361-8.
Liu, Y. 2024. Effects of sulfur dioxide fumigation on mortality of confused flour beetle (Coleoptera: Tenebrionidae) and rice weevil (Coleoptera: Curculionidae). Journal of Economic Entomology. Article toae156. https://doi.org/10.1093/jee/toae156.
Liu, Y.-B. 2024. Evaluation of fumigant toxicity of cyclohexanone to 5 species of insect pests. Journal of Economic Entomology. 117(2):494–499. https://doi.org/10.1093/jee/toae010.
Liu, Y.-B. 2024. Efficacy and phytotoxicity of sulfur dioxide fumigation for postharvest control of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), on select fresh fruit and vegetables. Agriculture. 14(2). Article 305. https://doi.org/10.3390/agriculture14020305.