Location: Crop Improvement and Protection Research
2019 Annual Report
Objectives
The long-term goal of this project is to develop alternative postharvest pest control treatments that are effective and safe for control of quarantine pests on a wide range of perishable agricultural commodities. This project builds upon our previous success with nitric oxide (NO) and oxygenated phoshine (PH3) fumigations as potential alternatives to methyl bromide fumigation for postharvest pest control on fresh fruits and vegetables. Nitric oxide was found to have higher efficacy than regular PH3 and may also enhance postharvest quality of fresh products. Oxygenated PH3 fumigation was found to control external pests with greater efficacy than regular PH3 fumigation. Successful completion of the project will result in specific NO fumigation and oxygenated PH3 fumigation treatments against four insect species on fresh fruit and vegetables including western flower thrips, light brown apple moth, codling moth, and the fruit fly spotted wing drosophila. Specific objectives are listed below:
Objective 1. Develop nitric oxide fumigation treatments for postharvest pest control.
Sub-objective 1.A. Develop an effective nitric oxide fumigation treatment to control western flower thrips on fresh fruit and vegetables.
Sub-objective 1.B. Develop an effective nitric oxide fumigation treatment to control light brown apple moth on fruit.
Sub-objective 1.C. Develop an effective nitric oxide fumigation treatment to control codling moth in apples.
Sub-objective 1.D. Develop an effective nitric oxide fumigation treatment to control spotted wing drosophila in sweet cherries and strawberries.
Objective 2. Develop oxygenated phosphine fumigation treatments for postharvest pest control.
Sub-objective 2.A. Determine feasibility of oxygenated phosphine fumigation to control codling moth in apples.
Sub-objective 2.B. Determine feasibility of oxygenated phosphine fumigation to control spotted wing drosophila in strawberries.
Approach
Objective 1. Nitric oxide fumigation under ultralow oxygen conditions will be studied for controlling insect pests including western flower thrips, light brown apple moth, codling moth, and spotted wing drosophila on harvested fresh commodities for their exports. Small scale laboratory fumigations will be conducted to determine effective treatments (concentration, time, and temperature) for different insects. Selected treatments will then be tested on specific fresh products to evaluate the impact of the treatments on postharvest quality.
Objective 2. Oxygenated phosphine fumigation under high oxygen conditions will be studied for controlling codling moth larvae in apples and spotted wing drosophila in sweet cherries and strawberries. Small scale laboratory fumigations will be conducted to determine effective treatments to control the most tolerant life stages of the pests in the fruits. Selected effective treatments will then be tested on fresh products to verify their efficacies and impact of postharvest quality of the fresh products.
Progress Report
Researchers in Salinas, California, expanded Objective 1 research to determine potential of nitric oxide (NO) fumigation in controlling fungi and bacteria on stored products. After successfully demonstrating the effectiveness of NO and nitrogen dioxide (NO2) against Aspergillus flavus spores and bacteria on stored almonds, a study was initiated to determine their effects on fungi and bacteria on stored, unshelled peanuts. Fungal infection is a serious concern on safety of stored products, such as peanuts, due to mycotoxin production by fungi. NO fumigation must be conducted under ultralow oxygen conditions and can be regulated to have desired levels of NO and NO2 and, therefore, has potential to control insects, fungi and bacteria in a single NO fumigation treatment. In this study, unshelled peanuts were fumigated with 0.3%, 1.0%, and 3.0% NO2 for three days at 25 degrees Celsius (C). After fumigation, wash-off microbial samples were taken before and after peanuts were crushed in order to sample microbes on exterior and interior surfaces of peanut shells. Preliminary results showed that all NO2 levels were effective in controlling fungi and bacteria, and that complete control occurred in the 3% NO2 fumigation treatment.
Research related to Objective 1 continued to evaluate methyl benzoate for its potential as an alternative fumigant for control of postharvest pests, including western flower thrips, lettuce aphid, rice weevil, and bulb mites. Complete control of all four pests was achieved in 8 to 72 hours, depending on pest species, with no adverse effect on apple quality. Additional fumigation tests are being conducted to demonstrate effectiveness of methyl benzoate as an alternative fumigant for postharvest pest control.
Accomplishments
1. Nitric oxide fumigation-controlled Aspergillus flavus spores on stored products. Aspergillus flavus infection is a serious problem for many stored products because the fungus produces carcinogenic aflatoxin. Nitric oxide (NO) fumigation containing NO and Nitrogen dioxide (NO2) controls insects and microbes on stored products. A researcher at Salinas, California, evaluated NO2 fumigation for its potential to inactivate Aspergillus flavus spores. Three-hour fumigation treatments at 0.1% NO2 or 1.0% NO at 15 degrees Celsius completely inactivated A. flavus spores. The study indicated that NO fumigation for pest control also has potential to control fungus spores on stored products.
2. Nitrogen dioxide fumigation-controlled microbes on stored almonds. Postharvest control of microbes is critical for preventing spoilage of stored products such as almonds. Nitric oxide (NO) fumigation containing NO and Nitrogen dioxide (NO2) controls insects and microbes on stored products. A researcher at Salinas, California, evaluated NO2 fumigation for its potential to control bacteria and fungi on stored almonds. Unpasteurized almonds were subjected to one- and three-day fumigations with 0.1%, 0.3%, and 1.0% NO2 at 25 degrees Celsius. All treatments were effective in controlling bacteria and fungi, and they were completely controlled at 1% NO2. The study adds further evidence on the potential of NO fumigation for control of both pests and pathogens on stored products.
3. Nitric oxide fumigation residues on stored products minimized to insignificant levels by nitrogen flush. Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control and understanding its residues on fumigated products is important for its potential applications in the future. A researcher at Salinas, California, measured residues of NO fumigation including nitrate, nitrite, and nitrogen dioxide on nine stored products including almond, barley, garbanzo bean, pecan, pinto bean, pistachio, rice, walnut, and wheat at different times after fumigation. NO fumigation must be conducted under ultralow oxygen conditions and terminated with nitrogen gas (N2) flush to prevent its reaction with oxygen to form nitrogen dioxide. When terminated properly with N2 flush, nitric oxide fumigation did not significantly increase levels of nitrate or nitrite on fumigated products and there was also no significant difference in nitrogen dioxide dissipation rate between the treatment and the control at 21 days after fumigation. Fumigation treatments that were terminated with air flush, however, resulted in significantly higher residue levels as compared with controls. The study provided residue data which are important if NO is to be registered as a pesticide and demonstrated that termination with N2 flush is important to prevent increases of residues and that properly conducted nitric oxide fumigation does not leave significant levels of residues in fumigated stored products.
Review Publications
Liu, Y. 2019. Sulfur dioxide fumigation for postharvest control of mealybugs on harvested table grapes. Journal of Economic Entomology. 112:597-602. https://doi.org/10.1093/jee/toy373.
Liu, Y., Oh, S., Jurick II, W.M. 2019. Response of Aspergillus flavus spores to nitric oxide fumigations in atmospheres with different oxygen concentrations. Journal of Stored Products Research. 83:78-83. https://doi.org/10.1016/j.jspr.2019.06.001.
