The California Department of Pesticide Regulation’s (DPR) pending decision to approve methyl iodide as a soil fumigant replacement for methyl bromide has received considerable public attention in the media in recent months. The fumigant, already approved federally by EPA in 2007 and used on more than 15,000 acres in the U.S., mostly in strawberries and vegetables in the Southeast, is awaiting final registration at the state level this summer.

IN A REPLANT TRIAL by Dr. Mike McHenry, nematologist and Extension nematology specialist at the UC Kearney Agricultural Center, young almond trees in the foreground were planted in untreated soil while the almonds in the background were planted into fumigated soil. The few options for fumigation that do exist are going to become more costly and complicated to apply, with or without California registration of methyl iodide.

Led largely by a campaign spearheaded by the Pesticide Action Network, a public advocacy group based in San Francisco, DPR received an unprecedented 50,000 comments and e-mails from the public during a recent 60-day public comment period ending June 29.

Much of the controversy surrounds the risk of exposure to applicators, workers and the public. There is no argument that fumigants by their nature carry risks when not handled properly. What is often ignored, however, are the great lengths to which registrants and state and federal agencies go to mitigate those risks. Balancing a compound’s risk against its benefits of use and the ability to mitigate those risks is an important function of the registration process. Years of data and review go into that equation for every pesticide labeled for agricultural use.

DPR’s proposed state label for methyl iodide goes well beyond already onerous restrictions on the use and application of methyl iodide at the federal level. State requirements would set maximum exposure levels for professional applicators at half the federally allowed level and just one-fifth the federal standard for field workers and neighbors. The state is also proposing large buffer zones ranging from 100 feet to a half-mile, along with reduced application rates and application limits on treated acreage to protect ground water. Compare that to Japan and Australia, where methyl iodide is being used with no buffer zones at all.

If methyl iodide is registered for use in California, growers will have to understand the mitigation measures as well as the soil and pest combinations they have present to determine when using it makes sense. For example, the current restrictions allow a maximum of 20 acres to be treated at one time with shank injections along with the use of a VIF tarp. Cost will also be a major factor in deciding which fumigant or combination of fumigants to use.

Almond growers fumigate the soil prior to planting for three distinct reasons: 1) reduce the impact of replant disorder when planting new orchards to ground that have previously been planted to tree or vine crops; 2) combat soilborne pests such as nematodes; and 3) destroy diseases, including Armillaria root rot (oak root fungus), a particularly tough disease that can lay dormant in dead roots under the soil for years, but will ultimately kill off trees within an orchard. Proper analysis of the soil, history of use, and previous problems can help guide the decision of when and which fumigant to use.

Research and experience have shown that there is a startling difference in tree growth and production once an orchard becomes established on ground that is fumigated compared to ground that is not where replant disorder or nematodes are an issue.

The California Almond industry for years has funded research to find alternatives and solutions to these vexing below ground problems, particularly as methyl bromide has been phased out under terms of the 1990 Montreal Protocol. In the case of replant disorder and nematodes, alternatives do exist, although methyl iodide combined with chloropicrin has proved to be an additional option.

Fallowing land for a year prior to replanting to ground where almonds or stone fruits were planted can help with replant disorder. Growers must weigh the benefits against the cost of losing an extra year of production. In research supported by the Almond Board of California, a recent trial looked at the efficacy of methyl iodide used in a premix with chloropicrin under the brand name Midas for replant disorder. The trial found that Midas used as a strip or broadcast treatment provided some of the greatest yield benefits compared to untreated and alternative treatments.

A mixture of Telone and chloropicrin provides good protection against nematodes, but Telone has its own significant use limitations. There again, methyl iodide mixed with chloropicrin has proved to be a viable alternative.

For the estimated 5 percent to 10 percent of the state’s almond acreage that is plagued by oak root fungus, there simply are no good available alternatives to methyl bromide. Research has shown that methyl iodide works similarly to methyl bromide to penetrate deeply into the soil, and thus is likely to become the material of choice to kill the oak root pathogens.

Methyl iodide can also be an important methyl bromide alternative for nurseries to ensure that certified stock is completely free of nematodes and disease.

With or without the registration of methyl iodide, California growers are going to find it even more difficult and expensive to fumigate in coming years. EPA is in the process of developing more stringent label restrictions that will begin showing up on most registered fumigants around the first of the year to protect neighbors and farm workers from risks associated with soil fumigation.

In the end, the costs and requirements for applying all soil fumigants, including methyl iodide, will continue to mount and growers will have to make difficult decisions about how best to protect their crops from below-ground predators in an increasingly complicated and expensive regulatory environment. For information on coping with fumigant regulations, go to AlmondBoard.com/farmpress10.