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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

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.

Postharvest alternative

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 [industry] are asking difficult things from us. It’s not like treating fruit in bins. The boxes are tougher by far."

The system works well when fruit are in bins, but in boxes, the airflow must go through four boxes—and the boxes, which only have small vents, were not designed with CATTS in mind. Obenland said the small plastic totes used to pick cherries show promise, but that the standard cartons used by industry may need airflow redesign before they will work.

"We’re hoping that Dave can overcome the problems of heating up the fruit in boxes in a timely and uniform manner," said Gary Van Sickle of the California Tree Fruit Agreement. Stone fruit are more delicate and don’t take to the secondary handling that would be required if bins are the only effective way to use CATTS, he added.

"It may be that the box needs to be redesigned to achieve what we want," Van Sickle said.

The CATTS research has been funded by the Washington Tree Fruit Research Commission and the California Tree Fruit Agreement.

Export markets

Both tree fruit industries in Washington and California are interested in CATTS for its potential to allow tree fruit to be exported without fumigation to countries like Japan.

California’s primary target for CATTS is Japan, Van Sickle said, adding that California’s stone fruit industry (aside from cherries) has not shipped fruit to Japan for the last two years.

"The industry backed off from Japan because methyl bromide fumigation is hard on the fruit, and the protocol calls for a Japanese inspector to come over here, which costs about $600 to $700 a day," Van Sickle said.

Fumigation was once the only way to send fruit to Mexico, he added. But
in recent years, the list of quarantined pests for Mexico has been reduced, and the country has approved a systems approach for quarantine pests.