• Introduction
• Preplant Soil Fumigation Alternatives
• Postharvest Commodity Treatment (Including Structural)

Introduction

This National Program focuses on finding alternatives for methyl bromide, an important soil and postharvest fumigant that is scheduled to be banned in 2005 because of its deleterious effect on the stratospheric ozone layer.  In addition to the $14.7 million provided by Congress in FY 2000 to ARS to conduct this research, USDA provided an additional $800,000 to speed up efficacy and environmental fate testing of propargyl bromide, a promising alternative to methyl bromide.  The FY 2001 budget appropriation contains an additional $620,000 for research on methyl bromide alternatives for the floriculture industry.

Selected Accomplishments (Listed by Component)

Preplant Soil Fumigation Alternatives

Non-chemical control of red stele disease.  Red stele disease is a serious fungal disease of strawberries, which is often controlled by methyl bromide fumigation.  Scientists at Beltsville, Maryland, showed that a cover crop used in combination with several cultural practice changes (raised beds with plastic mulch, greenhouse runner plug plants, and drip irrigation) could eliminate this disease even when environmental conditions were favorable for disease expression.  Even susceptible strawberry varieties showed no disease.

Identification of Pythium species to aid in development of control strategies.  Pythium is an economically important pathogen of many crops including peppers.  Scientists at Ft. Pierce, Florida, working in collaboration with University of Florida scientists, identified 11 Pythium species that colonize pepper root systems on commercial farms in Florida.  It was determined that 4 species can cause significant root rot and reductions in growth of peppers and tomatoes.  This research contributes to a greater understanding of the ecology of this pathogen and provides information useful in developing control strategies after the use of methyl bromide is banned.

Biological treatment for vegetable and strawberry transplants.  Plant growth and yields with alternative fumigants do not yet equal those achieved through the use of methyl bromide.  Working with a commercial company, scientists at Ft. Pierce, Florida, developed biological treatments for vegetable and strawberry transplants that resulted in increased plant growth and yield.  This research has resulted in a new commercial product consisting of a formulation of plant growth and yield-enhancing microorganisms.  This technology provides vegetable and strawberry growers with additional viable technology for use in combination with methyl bromide alternatives to mitigate yield losses.

Barrier film 'Hytibar' decreased the emission rates of 1,3-dichloropropene.  Because of air pollution issues, the use of 1,3-dichloropropene, one of the most effective methyl bromide alternatives is restricted in California and potentially other parts of the country.  Scientists in Gainesville, Florida, in cooperation with University of Florida scientists, showed that use of the barrier film 'Hytibar' decreased the emission rates of 1,3-dichloropropene significantly compared to standard polyethylene row-covers, which resulted in a 2- to 4- fold greater concentration of the substance in the soil over a 24- to 72- hour period.  The greater soil retention not only reduces the risk of air pollution but also increases efficacy of this methyl bromide alternative allowing for reduced application rates.

Identification of two bacterial pathogens that cause disease and affect crucifer production.  Bacterial diseases of crucifers are becoming increasingly important in central California.  Many of these pathogens have not been identified or characterized and are likely to increase in importance with the loss of methyl bromide.  Scientists at Salinas, California, identified two bacterial pathogens that cause disease and affect crucifer production, determined that crop residue in soil may be an important inoculum source, and are determining if these pathogens are affected by cultural practices.  Targeted, non-methyl bromide control strategies will be developed for these pathogens.

Chemical treatments control grape replant disorder.  Effective alternatives to methyl bromide are needed for controlling grape replant disorder when replanting table, wine, or raisin grape vineyards.  Scientists at Fresno, California, along with a scientist from the University of California, Riverside, showed there was no significant difference in control of plant parasitic nematodes 24 to 28 months after treatment with methyl iodide, four different Telone+Vapam treatments, and methyl bromide.  From an efficacy standpoint, these treatments are viable alternatives to methyl bromide for grape replant disorder.

Application of methyl bromide alternatives by drip irrigation.  Scientists at Fresno, California, in cooperation with the California Strawberry Commission and several chemical companies, developed and demonstrated innovative drip application technology as a low risk means of applying alternative fumigants.  Drip irrigation application of alternative fumigants is now being pursued by several chemical companies and fumigant applicators in California.  This technology may provide a practical and environmentally sound fumigation method that will allow continued high productivity of high-value fruit and vegetable crops after methyl bromide is phased out.  

Postharvest Commodity Treatment (Including Structural) 

Hot forced air treatment for grapefruit, navel oranges, and tangerines.  Cooperating with USDA APHIS Plant Protection and Quarantine officials, scientists at Weslaco, Texas, developed and published the treatment requirements for grapefruit, navel oranges, and tangerines using hot forced air to meet United States quarantine requirements against Mexican fruit flies.  Commercial shipments to the United States have started under this protocol.  This treatment was shown to be an effective commercial replacement for methyl bromide fumigation for this quarantined pest. 

 Solbait will kill 50 percent of fruit flies.  Outbreaks of exotic pests result in increased methyl bromide use to fumigate commodities leaving the quarantine zone until eradication is complete.  Better, more environmentally friendly eradication tools would minimize the use of methyl bromide under these emergency conditions.  Scientists at Weslaco, Texas, have shown that a concentration as low as 0.159 parts per million (ppm) in 'Solbait' will kill 50 percent of fruit flies.  When sprayed in a 80 ppm formulation, Spinosad remained active for 21 days, which compares favorably to Malathion, the most common fruit fly bait spray treatment.  An added advantage of the Solbait formulation is that it repels honeybees and other beneficial insects, sparing them from toxic effects of the Spinosad.

Radio frequency energy eliminates insect pests from fruits.  An important use of methyl bromide is for fumigation of export and import commodities to eliminate quarantined pests.  Research conducted at Wapato, Washington, in cooperation with a scientist at Washington State University, showed that radio frequency energy could successfully eliminate insect pests from fruit.  Codling moth larvae in sweet cherries and apples were destroyed without damaging the fruit.  Although this technology is in its infancy, this research provides the possibility for a new strategy to replace methyl bromide fumigation.

Non-fumigation treatment for mangoes exported from Hawaii to the United States Mainland.  Scientists at Hilo, Hawaii, showed that 100 Gy of irradiation could disinfest mangos of mango seed weevils.  Accordingly, USDA has proposed to allow treated Hawaiian mangoes into the Mainland for the first time in 50 years.  This export outlet for Hawaiian mangoes will encourage the further development of Hawaiian mango production. 

Better insect exclusion practices decrease need for prune fumigation.  Prunes are insect free after dehydration.  Preventing their reinfestation would reduce or eliminate the need for chemical fumigants such as methyl bromide.  Scientists at Fresno, California, in collaboration with a scientist from the University of California, Davis, tested the ability of plastic bin liners already used for other purposes by the prune industry to exclude insects from the product.  The bin liners were found to be easily punctured and allowed newly hatched larvae to gain access to the prunes.  Insect resistant liners would greatly reduce insect infestation and reduce the need for additional fumigation of prunes in storage.

Methyl iodide a promising alternative to methyl bromide.  Scientists at Fresno, California, evaluated methyl iodide, sulfuryl fluoride, and carbonyl sulfide, all promising alternatives to methyl bromide for postharvest fumigation, of lemons and nectarines.  Methyl iodide was found to be the most promising when a postharvest aeration of 24 hours was used.  This treatment significantly reduced fruit phytotoxicity and, if registered, would be an effective methyl bromide replacement.