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Soil fumigation, like this broadcast application, now requires that fumigation management plans be developed to include a long list of components.

Soil fumigation, like this broadcast application, now requires that fumigation management plans be developed to include a long list of components.

The soil fumigation landscape has changed ­dramatically in the last few years. Effective postplant nematicides have been lost, use of methyl bromide as a soil fumigant is on the way out, and now, soil fumigation in general will be more restrictive as new U.S. Environmental Protection Agency regulations begin to take hold.

Dr. Inga Zasada, nematologist at the U.S. Department of Agriculture Agricultural Research Service’s Horticultural Crops Research Unit in Corvallis, Oregon, works to develop sustainable plant-parasitic nematode management systems for small fruits. Her research involves developing economic thresholds for plant-parasitic nematodes, developing production systems that promote root health and suppress such nematodes, and providing information on efficacy of management strategies, including nematicides, biologicals, and cover crops.

She recently outlined the changes taking place in the world of soil fumigants.

Postplant control

Since the voluntary cancellation in 2008 by Bayer Corporation of Nemacur (fenamiphos) because of association with bird kills, growers have had few effective postplant chemicals to control nematodes in established orchards and vineyards. “Since Nemacur’s cancellation, postplant control has been very difficult, with very few options,” said Zasada. “All perennial crops suffer from the lack of postplant nematode control options.”

Options include the postplant chemical Enzone (sodium tetrathiocarbonate), registered to control phylloxera, nematodes, and certain fungi in established grapes and tree fruit, she said. There are a few biological nematicides available, but they give inconsistent results.
Brassica and mustard crops, like Braco mustard, arugula, and Caliente mustard, can be effective as bio­fumigants, releasing chemical compounds that may be toxic to soilborne pathogens, nematodes, fungi, and some weeds. However, their effectiveness depends on the target pest, plant species being incorporated, proper timing of soil incorporation, and soil moisture.

Zasada noted that a new postplant nematicide Cordon is seeking registration approval for use in grapes in California. Cordon contains a very low concentration of Telone (1,3-dichloropropene) and is applied through drip irrigation. Trials in Prosser, Washington, showed that fall treatments worked better than spring applications, according to Zasada. This ­product is not currently registered in Washington.

Soil fumigation restrictions

Fumigating the soil before planting has long been recognized as a useful practice to clean up nematodes and combat replant disease. Starting clean is usually more effective in the long run than continually treating fields after vines or trees are established. “It’s always a struggle to deal with nematodes after the fact,” Zasada said.

But preplant fumigation procedures became more restrictive this year because of the U.S. Environmental Protection Agency’s fumigant reregistration eligibility decisions initiated in 2009. As part of the reregistration eligibility process, new labels include fumigation management plans and buffer zones to reduce exposure to users and bystanders. Fumigants included in the reregistration process are chloropicrin (commonly combined with Telone), dazomet (granular Vapam), iodomethane (Midas—registered in California but not Washington), metam sodium (Vapam), and methyl bromide. Methyl bromide is no longer available for use in plantings of grapes or tree fruits.

New labels for the fumigants came out in December 2010, she said. “You now have to have a site-specific fumigation management plan that includes keeping records for two years from the date of application.”

Components of the fumigation management plans include:

  • Applicator information
  • General application information
  • Tarp information (if this applies)
  • Soil conditions (texture, moisture)
  • Weather conditions
  • Personal protective equipment
  • Emergency procedures
  • Posting procedures
  • Communication plan
  • Authorized on-site personnel
  • Air monitoring plan
  • Good Agricultural Practices
  • Description of hazard communication (posting, available labels)
  • Record keeping (applicator and owner/operator must retain records for two years)

Thirty days after fumigation, a postfumigation application summary must be completed that describes any deviations from the fumigation management plan that occurred.

Buffer zones

But the real cumbersome EPA regulations kick in later this year, Zasada said. Buffer zones are expected to be included on the labels in December 2011 or early in 2012. Buffer zones around the application site allow airborne residues to disperse before reaching bystanders.

Growers will have to determine the size of the buffer zone based on application rate, field size, application equipment and method, and credits for emission-reduction measures, like tarps and site conditions, she explained. The perimeter of the buffer zone must be posted, and the buffer zone period starts at the moment when any fumigant is delivered to the soil and lasts for a minimum of 48 hours after the fumigant has stopped being delivered to the soil.

“Moreover, buffer zones may not include inhabited structures unless the occupants provide written agreement that they will voluntarily vacate the buffer zone during the entire buffer zone period,” she said.

Regardless of the 25-feet minimum buffer zone, you can’t fumigate if your field is within 1/8 mile of a difficult-to-evacuate site (for example, school, daycare center, or nursing home), unless the site is not occupied during the application, she added.

Zasada discussed the soil fumigation changes during the Washington Association Wine Grape Growers annual meeting.

Additional information about the EPA reregistration eligibility decisions can be found at www.epa.gov/opp00001/reregistration/soil_fumigants/.