A new soil fumigant was recently registered—the first new registration since methyl bromide was classified as an ozone-depleting substance and phased out. On the postharvest side, scientists are still working on the commercial feasibility of an alternative for pest quarantine treatments.
The new fumigant methyl iodide or iodomethane—the first to be approved in 20 years by the U.S. Environmental Protection Agency—holds promise for growers looking to replace the broad-spectrum methyl bromide fumigant that was phased out on January 1, 2005. The EPA did allow some exemptions as part of the phaseout agreement—preshipment uses to eliminate quarantine pests and critical use exemptions designed for agricultural users with no technically or economically feasible alternatives for soil fumigation.
Methyl iodide, originally patented by scientists at the University of California, Riverside, sells under the trademark name MIDAS by registrant Arysta LifeScience. The EPA granted a one-year registration in October for use on tree fruits, strawberries, tomatoes, peppers, ornamentals, nut crops, vine crops (including wine and table grapes), turf, and nursery crops. The agency also required buffer zones as part of the registration based on fumigant rate and the number of acres treated to further ensure safety.
Large-scale commercial trials of methyl iodide were conducted under the EPA’s experimental use permit program, which allowed up to 1,000 acres to be treated since 2006 in Florida, Georgia, Michigan, North Carolina, South Carolina, Tennessee, and Virginia. The EPA added test acreage in California in 2007.
According to Arysta LifeScience, more than half of the growers who participated in side-by-side trials with methyl bromide saw a 19 percent increase in yields with the MIDAS-treated acreage. The remaining growers saw yields on par with the methyl-bromide-treated acreage.
The chemical is considered a "drop-in" replacement for methyl bromide, as it provides the same broad spectrum of nematode, weed, insect, and pathogen control. Since the phaseout, some growers have used a combination of fumigants to achieve the same broad spectrum of control that methyl bromide provided.
The new preplant fumigant, though it shares many of the same chemical properties as methyl bromide, is effective at lower rates than methyl bromide and breaks down rapidly under ultraviolet light.
For more than a decade, U.S. Department of Agriculture scientists have studied using controlled atmosphere and temperature to kill quarantine pests of tree fruit as an alternative treatment to methyl bromide fumigation.
Dr. Lisa Neven, research entomologist with the USDA near Yakima, Washington, devised the controlled –atmosphere and temperature treatment system, known as CATTS. Fruit placed inside a computer-controlled chamber are heated to around 111°F to 115°F. At the same time, oxygen levels are reduced to around 1 percent, and carbon dioxide levels are raised to 15 percent.
Neven said that her part of the research on apples and cherries is "about done." She has proven that quarantine pests like codling moth, Western cherry fruit fly, and Oriental fruit moth are killed by the treatment. She has also collected data on apple maggot and plum curculio.
"The hurdle is now on commercialization," Neven said. "Once we get commercial units up, I will help run efficacy trials. Then I’ll be looking for other work."
Another researcher involved with CATTS is Dr. David Obenland, postharvest physiologist at USDA in Parlier, California. Obenland has answered the question of –treatment efficacy on stone fruit. He is now working to expand the treatment from bins to packed boxes of peaches, nectarines, and apricots.
In the beginning, Obenland conducted stone fruit trials in USDA’s small research chamber and a commercial prototype unit located in George, Washington. The commercial prototype chamber, which holds up to four bins at a time, was built a few years ago by Harold Ostenson and Dan Black of TechniSystems LLC in Chelan, Washington. At the time, Ostenson was owner of PAC Organic in George. He’s now manager of the organics program at Stemilt Growers, Inc., Wenatchee, Washington.
Obenland began using a larger chamber built at the Parlier station earlier this year with funds from a USDA grant. The chamber accommodates two pallets of fruit or about 160 boxes. Unfortunately, it was installed too late in the season to collect much data. But Obenland knows the challenge before him is daunting.
"It’s not going to be easy," he said. "They