Proper soil fumigant application critical for producer, crops

Though soil fumigants have been around for many years, some growers may need to use these gas pesticides for the first time in 2006, and may not be familiar with the dangers of these soil-applied products.

Growers producing high dollar per acre crops, most prominently vegetable crops, have been the traditional users of Telone and other popular fumigants. With the decrease in tobacco acreage in the upper Southeast, many growers have turned to niche crops, including vegetables, which often require soil fumigants for controlling weeds, disease and nematodes.

Increase in popularity of zone sampling and other precision agriculture techniques has allowed growers to determine high risk areas in a field. Whereas large acreages are not likely candidates for soil fumigants, small pockets within these fields often are feasible, even for traditional row crops.

Combined, the potential is good for an increase in fumigant use in 2006. “Failure to use fumigants properly can cause harm to the crop, to humans and to the environment,” notes Jim Burnette, administrator for the North Carolina Department of Agriculture's Pesticide Section. Burnette adds that fumigants are safely used everyday, but stresses that special precautions must be used to protect everyone involved in or near application of these products.

Fumigants are volatile substances and change into gases upon injection into the soil as liquids. Fumigant vapors can only move through continuous air space in the soil. Fumigants move through soil air, dissolve in soil water and kill targeted pest in the soil water.

Applying proper amounts of fumigants is tricky, but critical to achieve maximum control for minimum cost, and with the least possible degradation to the environment — and harm to human applicators. The objective of soil fumigants is to establish a lethal concentration and maintain it for a sufficient amount of time to kill the target organism as it makes its way through the soil.

The ability of a fumigant to move through the soil varies with soil type. It is more difficult for fumigants to move through heavier clay soils than through lighter sandy soils. Therefore, a clay or silty loam soil should be dry when fumigants are applied, while sandy soils can be wet and still achieve good results.

Restrictions and requirements for proper fumigant application include additional training for personnel involved in applying these gas pesticides. Additional soap and water should be on hand for a quick and thorough wash, if a user is subjected to vapors from the release of a fumigant. Growers are also required to post signs in fields in which fumigants are applied.

Burnette stresses the importance of growers being familiar with specific restrictions for various fumigants. Growers are responsible for knowing the safety requirements of all pesticides they use, and Burnette says, “growers should always contact the fumigant manufacturer for information and training.”

The North Carolina administrator notes the labels for fumigants, and other pesticides, change frequently and safety requirements are often updated with these changes.

“People who don't follow requirements and restrictions on pesticide labels can be in violation of North Carolina's pesticide laws,” Burnette stresses.

Because pesticide fumigants are applied as liquids and convert to gas in the soil, and usually before planting, changes in environmental conditions can significantly affect how these products work. Improper application or timing of fumigants can cause personal or environmental damage, but is more likely to result in these expensive materials not working properly.

Each fumigant label addresses soil temperature or moisture conditions for optimum performance and safety,” Burnette says. Reduced soil moisture content during dry periods decreases the soil's ability to seal and keep the fumigant in the ground, he adds. Low soil temperatures that are typical in the upper Southeast in April and May also decrease the effectiveness of some fumigants, he explains.

When using fumigants, producers should pay careful attention to crops and people in adjacent areas, especially low-lying areas near the application site. Burnette explains that calm wind conditions and atmospheric inversions, occurring when air in the upper atmosphere is warmer than air below, can cause fumigants to linger in low lying spots and settle over adjacent areas.

The use of cover crops may serve as an alternative to fumigation as well as mitigating degradation to soil and environmental quality. Soil erosion continues to be a threat to agricultural productivity worldwide, with soil losses in the United States alone exceeding three billion tons annually.

Despite the inherent physical and financial risk involve in using soil fumigants and possible replacement by cover crops, these products can be effective tools, and in some situations the last option to protect a crop from soil-borne pests.

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