Published January 15, 2011

Over the past 25 years, 130,000 acres of orchards have been replanted in Washington State, requiring a total investment of $1.7 billion, estimates Tim Smith, Washington State University Extension educator in north central Washington.

Sometimes, the trees grew well and recouped the investment, but occasionally they didn’t because of replant disease. This disease can affect any tree fruit that is planted in ground where tree fruits have been grown before. It results in poor tree growth and productivity because of a build-up of microorganisms in the soil. Recommended treatment is fumigation of the ground before planting.

Smith said nowadays 60 percent of replanted orchards are fumigated, but he feels it should be 100 percent. Smith tracked production in a Gala orchard in north central Washington from when it was planted in 1985 until it was removed in 2002 and said greater yields in the fumigated parts of the orchard generated additional income of $67,000 per acre over the life of the orchard.

“I use this argument when people say, ‘I don’t fumigate because it costs too much,’” he said. “The first two to three bins are going to pay for the fumigation.”

Smith said it is not possible to overcome the effects of fumigation by planting at higher densities. And, rootstocks that are tolerant of replant disease aren’t totally immune and also perform better in fumigated ground. However, more restrictive rules being introduced by the U.S. Environmental Protection Agency will make fumigation more difficult and will probably rule out growers doing their own fumigation.

New rules

Some of the EPA’s new regulations went into effect in December 2010 and others will be on fumigant labels by late 2011.

The following rules are now in effect or soon will be for all registered fumigants.

Worker protections: Existing labels required handlers to use respirators when air concentrations reach certain levels. New labels require handlers to stop work or put on respirators if they experience sensory irritation. Respirators must be tested and handlers trained how to use them. The minimum interval between application and removal of the tarp covering is five days, and the minimum worker reentry period is five days or until after the tarps are perforated or removed.

Applicator training: Registrants must provide safety information for fumigant handlers about practices that can reduce exposure to fumigants and improve safety for workers and bystanders.

Good Agricultural Practices: Practices to reduce off-gassing and improve the safety and effectiveness of applications that were previously only recommended on labels are now required. Good Agricultural Practices include proper soil preparation and tilling, applying fumigants during optimal soil moisture and weather conditions, use of sealing techniques, and equipment calibration.

Application methods and rates: Untarped applications of some fumigants are restricted, and maximum application rates have been reduced to reflect rates needed for effective use.

Classification: All fumigants are classified as restricted use pesticides. Previously metam sodium/potassium and dazomet were not.

Fumigant management plans: Fumigant users must prepare a written, site-specific fumigant management plan before fumigation begins. The plan must be kept for two years and be available upon request to federal, state, and local officials.

The following measures are scheduled to go into effect at the end of this year.

Buffer zones: Buffer zones around treated fields will be required to reduce risks to bystanders. The size of buffer zones will depend on the application rate, field size, application equipment and measures, and emission-control measures, such as tarps. Buffer zone distances will be shown in look-up tables on ­product labels.

Posting requirements: Buffer zones must be posted at usual points of entry and along likely routes taken by neighbors unless a physical barrier prevents access to the buffer.

Emergency preparedness: In areas where bystanders may be close to the buffer zones, fumigators may either monitor the buffer perimeter for fumigant or provide emergency response information directly to neighbors.

For more details check the Web site