Location: Crop Improvement and Protection Research
2025 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 is the final report for project 2038-22430-003-000D, Methyl Bromide Alternative Treatments for Perishable and Stored Products, which will be replaced by new project 2038-30400-001-000D, Alternative Treatments for Control of Pre-Plant Diseases and Postharvest Pests on Perishable and Stored Products.
In support of Sub-objective 1A, research was conducted to determine effects of nitrogen dioxide (NO2) fumigation on microbes on stored almonds and peanuts. Unpasteurized almonds were subjected to 1- and 3-day fumigations with 0.1%, 0.3%, and 1.0% NO2 at 25° degrees C. Microbes on fumigated almonds and untreated control were sampled after fumigation and microbial loads were determined using a rapid enumeration test system. All treatments were effective in control both bacteria and fungi and 1% NO2 had complete control of both bacteria and fungi on almonds. Peanuts were fumigated with 0.3%, 1.0%, and 3.0% NO2 for three days at 25° degrees C. Wash-off microbial samples were collected from intact and cracked open peanut samples to determine microbial loads on the samples. All three NO2 fumigation treatments showed significant antibacterial and antifungal effects on intact peanuts as well as on cracked peanuts with complete inhibition with 3.0% NO2. Fumigation did not have obvious effects on appearance of skinned peanut kernels. The results of these studies show that nitrogen dioxide fumigation has potential for microbial management on stored products.
In support of Sub-objective 1B, research was conducted to determine effective nitric oxide (NO) fumigation treatments against light brown apple moth (LBAM) and ham mites. Nitric oxide fumigation was tested against different life stages of LBAM in laboratory under ultralow oxygen conditions at 2°C. Complete control of larvae and pupae was achieved in 8 h fumigation with 2.0% NO. Eggs were successfully controlled in 6-, 12-, and 24-h fumigations with 5.0, 3.0, and 2.0% NO respectively. Ham mites at different life stages on artificial media were fumigated with 0.5 to 2.0% NO under ultralow oxygen conditions for 8- to 48-h to determine effective treatments. Complete control of eggs, mobile immatures, and adults was achieved, and eggs were more tolerant to NO than other life stages. Effective control of all life stages of ham mites on hams was also confirmed in 48- and 24-h fumigations with 0.5 and 1.0% NO, respectively. These studies demonstrated that NO fumigation has potential to be an alternative treatment to methyl bromide fumigation for control of LBAM on fresh products and ham mites on cured-ham products.
In support of Sub-objective 1C, sulfur dioxide (SO2) fumigation was evaluated for controlling western flower thrips and safety to four select fresh fruits and vegetables including broccoli, peppers, apples, and navel oranges. Complete control of thrips was achieved in 30- and 60-minute fumigations with 0.5% and 0.3% SO2 at 5 degrees C. The 30-minute fumigations with 0.3-0.5% SO2 of fresh products resulted in complete control of thrips and no injuries to peppers and navel oranges. However, the treatment caused severe injuries to broccoli and minor injuries in form of darkened lenticles on green apples. This study demonstrated that SO2 fumigation has potential to be a safe and effective treatment to control western flower thrips and other susceptible pests on certain fresh fruit and vegetables.
In support of Sub-objective 1C, SO2 fumigation was evaluated as an alternative treatment for postharvest control of navel orangeworm (NOW) on stored pistachios. Sorption of SO2 on pistachios were measured at different temperatures, and pistachios were found to have high sorption of SO2 over time. SO2 fumigations of 3 h were tested against eggs, larvae, and pupae to develop an effective SO2 fumigation treatment against NOW. Complete controls of eggs, larvae, and pupae were achieved in 3-h fumigations with 0.2, 2.0, and 1.0% SO2, respectively, and large-scale 3-h fumigations of pistachios with 1.6-1.8% SO2 had complete control of 6th instar larvae in infested pistachios. The results showed that SO2 fumigation has potential to control NOW on stored pistachios as well as to control other postharvest pests on stored products.
In additional support of Sub-objective 1C, SO2 fumigation was also evaluated for controlling confused flour beetle and rice weevil, two major stored product insects. Three-hour fumigations with 0.1 to 2% SO2 were conducted against all life stages of the two insects. Effective control of both species was achieved. However, there were considerable differences between the two species and among different life stages in susceptibility to SO2 fumigation. Confused flour beetle was more susceptible to SO2 fumigation than rice weevil. For confused flour beetle, complete controls of adults and all immature life stages were achieved in 3-h fumigations with 0.5 and 2% SO2 respectively. For rice weevil, 3-h fumigations with 2% SO2 resulted in 99.27% adult mortality and 87.5% mortality of immature life stages. This is the first study showing effective control of confused flour beetle and rice weevil with SO2 fumigation. Because SO2 is a generally recognized as safe compound (GRAS), SO2 has potential to be a safer alternative than most other fumigants for postharvest pest control on stored products.
In support of Sub-objective 1D, research was conducted to discover and evaluate new potential fumigants from volatile essential oil compounds. Anisole (methoxybenzene), a major essential oil compound from Pimpinella anisum seeds was found to be effective as a fumigant for controlling four insect species. Adults of granary weevil, rice weevil, and confused flour beetle were fumigated at 25° degrees C and western flower thrips were fumigated at 2° degrees C to determine effective treatments. Complete control of all species was achieved. Complete control of rice weevil adults at different depths in corn was also achieved. This study demonstrated that anisole has potential as an environmentally friendly fumigant for postharvest pest control.
In additional support of Sub-objective 1D, two more volatile compounds, cyclohexanone and chlorobenzene, were discovered to be effective as fumigants against different pests. Cyclohexanone, a major precursor for nylon production, was effective against five pests including rice weevil adults, confused flour beetle adults, western flower thrips larvae and adults, spotted wing drosophila adults, and subterranean termite workers in laboratory tests. Complete control of spotted wing drosophila adults was achieved in 1-h fumigation with 25 l/l of cyclohexanone while rice weevil and confused flour beetle adults were completely controlled in 24-h fumigations with 100 l/l of cyclohexanone. Three-hour fumigation resulted in 100% mortality of western flower thrips and eastern subterranean termites.
Chlorobenzene, the major precursor for pesticide dichlorodiphenyltrichloroethane (DDT) synthesis, was discovered to be an effective fumigant for pest control. Six insect species were tested, and effective control of all insects was achieved. The six insects represent diverse groups of pests, and they differed in susceptibility to chlorobenzene fumigation. Treatment times ranged from 1-h to 24-h depending on species and life stages. Its efficacy against confused flour beetle and rice weevil was also demonstrated in large-scale fumigations of corn. A United States patent application has been filed for the new fumigant. Research is continuing to develop chlorobenzene fumigation treatments against different pests.
Also in support of Sub-objective 1D, fresh produce including broccoli, bell pepper, apples, navel oranges, and strawberries were subjected to fumigation treatments with chlorobenzene for control of western flower thrips. Complete control of western flower thrips was achieved in 6- and 24-h fumigations at 2° degrees C. Chlorobenzene fumigation of 6-h for control of the thrips did not have significant effects on color parameters of green pepper, green apples, and navel oranges at 14 days after fumigation. Broccoli and strawberries showed significant difference in color between treatment and control. The fumigation treatment also caused discoloration of calyx of strawberries. The mixed results of this study indicate that chlorobenzene fumigation for control of western flower thrips is safe to postharvest quality of some fresh produces but may also cause injuries to susceptible fresh products. This research is still in progress.
Additionally, research was conducted to determine potential of long-term low oxygen (O2) storage for controlling stored product insects. Low oxygen storage treatments of 45 days with 3 to 8% O2 were studied for efficacy in controlling survival and development of rice weevil and confused flour beetle and different life stages were also subjected to a 14-day 5% low oxygen treatment to determine susceptibility of different life stages to the low oxygen treatment. There were considerable differences between the two species. Rice weevil eggs and adults were more susceptible to low oxygen treatment than larvae and pupae. For confused flour beetle, eggs were most susceptible and adults were most tolerant to the 14-day 5% low oxygen treatment. Results of the study indicated that long-term storage treatments with =5% and =6.5 O2 are expected to be effective to control rice weevil and confused flour beetle, respectively and long-term low oxygen storage treatment has potential to control rice weevil and confused flour beetle on stored products.
Additionally, research was conducted in collaboration with a plant pathologist at ARS in Salinas, California, to evaluate effects of nitrogen dioxide fumigation on survival of seed borne disease Verticillium on spinach seeds. Effective control of the disease was achieved with 3% nitrogen dioxide fumigation. The treatment did not have negative impact of seed germination as well as growth.
Accomplishments
1. Chlorobenzene is effective as a new alternative fumigant for control of stored product insects. The United States has phased out use of methyl bromide, once widely used as a fumigant for postharvest pest control. Unfortunately, there is a severe shortage of alternative fumigants that are similarly effective. ARS researchers at Salinas, California, tested chlorobenzene, the major precursor of the pesticide DDT (dichlorodiphenyltrichloroethane), for its efficacy in controlling two stored product insects, confused flour beetle and rice weevil. Chlorobenzene fumigation has high efficacy against the two stored product insects with an effective treatment time of 24 h and a lethal concentration for 95% mortality (LC95) of about 1100 ppm for adults of both species. In larger scale tests with corn, complete control of all life stages of confused flour beetle was achieved. Complete control of adults and 97.8% mortality of immature life stages were achieved against rice weevil. Chlorobenzene has low toxicity to mammals and is available commercially at a low cost and, therefore, has good potential as an alternative fumigant for postharvest control of stored product insects.
2. Ultralow low oxygen is an effective non-chemical alternative treatment to control spotted wing drosophila in small fruits. Spotted wing drosophila is a major fruit fly pest on soft fruits and affects exports of U.S. small fruits to international markets. Research was conducted to evaluate ultralow oxygen (ULO) treatments against this pest when coupled with a low storage temperature. ULO treatments of 3-4 days with 50-500 ppm O2 were effective against eggs and larvae of the pest in blueberries and cherries. Complete control of larvae was achieved in blueberries in a 3-day treatment. Four-day treatments resulted in over 90% of eggs in blueberries and 95% and >99% mortalities of eggs and larvae in cherries. Even though no complete control of both eggs and larvae was achieved, these results suggest good potential of ultralow oxygen treatments against spotted wing drosophila as well as other fruit fly pests and the impact may be further enhanced when used in combination with other treatments.
3. Beneficial microbes increase lettuce yield in plant pathogen infested fields. Soilborne plant diseases, like Verticillium and Fusarium wilt, are a significant constraint on lettuce production in the United States. Identifying practices that improve lettuce production in fields where these diseases are present will provide growers new tools to increase yields and profits. ARS scientists in Salinas, California, showed the application of the pathogen-antagonistic and plant growth promoting microbe Trichoderma harzianum as a soil drench increased lettuce yield in a field heavily infested with pathogens that cause Verticillium and Fusarium wilt diseases. Outcomes of this research demonstrate that beneficial microbes can improve lettuce health at the field scale, even when multiple soilborne diseases are present. Growers who want to increase yields will benefit from applying Trichoderma harzianum in lettuce.