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California almonds: Fumigation rules affect new plantings

Apr 1, 2008 10:28 AM, By Marni Katz
Contributing Writer

New state restrictions on the use of soil fumigants are expected to hit Ventura County strawberry growers hard, but these new rules will also have an immediate impact on the ability of San Joaquin Valley growers to fumigate ground for planting permanent crops like almonds and other tree and vineyard crops.

The new regulations will apply to the use of all seven fumigants with the potential to release volatile organic compounds (VOCs) during the months of May through October. These include methyl bromide, 1,3-Dichloropropene (Telone), chloropicrin, metam-sodium, metam-potassium, dazomet, and sodium tetrathiocarbonate.

Almond growers rely on soil fumigation to prevent orchard replant disorder when they pull out aging orchards to replant new trees. Soil fumigation is the best way to destroy microorganisms that can otherwise jeopardize the growth and yield potential of young new orchards, said Roger Duncan, a University of California Cooperative Extension farm advisor in Stanislaus County.

Duncan said that while there is still a lot unknown about the orchard replant problem, researchers and growers agree it is likely a combination of nematodes and other biological organisms that cause the soil to reject newly planted trees.

“Fumigation alleviates that, especially methyl bromide because it is a wide-spectrum biocide,” Duncan said.

Chloropicrin, which helps target biological agents, and Telone, a nematicide, are also commonly used in almonds.

The problem is particularly acute in sandier soils but can impact growth across all soil types, Duncan said.

“With sandier soils we know we need a fumigant, but we guess growers would also see a growth response in heavier soils as well,” he said.

The California Department of Pesticide Regulation in January enacted the long-discussed new regulations on soil fumigants for regions of the state with the dirtiest air — the San Joaquin Valley, Southeast Desert and Ventura County. They are part of DPR’s effort to curb emissions of smog-forming volatile organic compounds (VOCs) during the peak ozone period from May 1 to Oct. 31.

These restrictions are intended to reduce pesticide VOC emissions by 20 percent compared to 1991 levels, as required by a 2006 court order. Emissions reductions through changes in timing and application method are the focus for 2008. Starting in 2009, caps on soil fumigant use will go into place for those remaining non-attainment air quality areas. This allocation plan will significantly impact the availability of preplant soil fumigants to almond growers in the San Joaquin Valley in 2009.

“If an almond grower wants to do any kind of soil fumigant application between May 1 and Oct. 31 for the 2008 growing season, he needs to be aware that methods of application will be limited to so called lower emission methods,” said Gabriele Ludwig, senior manager of global technical and regulatory affairs for the Almond Board of California.

Ludwig said almond growers looking to use soil fumigants on orchard replants must now rely on lower emission application methods or alter their timing outside of the peak ozone period from May 1 to Oct. 31.

Under terms of the new rules, methyl bromide and chloropicrin applications during that period are limited to deep shank broadcast applications and must be tarped, which more than doubles the application cost, Duncan said.

Telone applications must meet more stringent soil moisture requirements. But Telone tends to bind in water, reducing its efficacy in higher soil moisture conditions. For a full list of requirements, check the DPR Web site under VOCs.

To get around these application requirements, growers have the option of moving their fumigations outside the ozone window. But timing applications during cooler months from November to April could reduce their performance, as fumigants work best under dry, warm soil conditions.

If DPR does not hit its VOC reduction target through changes in application rates and timing, then beginning in 2009, growers will be required to petition their county agricultural commissioner for the use of a soil fumigant to early in the calendar year. Based on those applications, DPR may cut the requested fumigant amounts if they exceed the VOC estimated emissions targets for the ozone season.

Filing petitions with county ag commissioners early in the season can also be challenging, because growers often don’t know at that time what their fumigation plans will be.

“A lot of times a grower doesn’t know if he’s going to take an orchard out and fumigate during this period,” Duncan said.

In addition, in 2009, PCAs statewide who do soil fumigations will be required to meet special training and licensing requirements. Despite the challenges, the new regulations are now here and growers will have to learn to work around them. Industry input has helped create a more workable set of rules in contrast to earlier drafts of the regulation. Still, experts say it’s now up to almond growers to seek guidance on how to integrate those rules into their operation, especially if they are planning to replant an orchard.

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