"Fifteen years ago, the Netherlands was one of Europe's major users of methyl bromide for soil fumigation," says Joop A. Van Haasteren. "But we no longer use it. In 1967, mechanically injecting methyl bromide in greenhouse soil became controversial. Consequently, our government imposed more stringent requirements on the use of this and other fumigants, and eliminated the use of methyl bromide for soil fumigation in 1991."

However, methyl bromide is still used in the Netherlands to fumigate stored products, structures, furniture, and as a quarantine treatment, according to Van Haasteren. He is with the Netherlands Ministry of Housing, Planning, and Environment.

Prior to the phaseout, Dutch growers used about 3,000 tons of methyl bromide annually to control soilborne pests on greenhouse-grown crops such as tomatoes, lettuce, strawberries, cucumbers, sweet peppers, as well as nursery crops and cut flowers. However, only small amounts were used to fumigate soil for field crops.

Instead, growers in the Netherlands now use soil-less mixtures of artificial and natural-growth compounds, steam sterilization, and chemical and nonchemical alternatives.

"We also rely on crop rotation," Van Haasteren explains. "And, we've had good results with chemical substitutes such as metam sodium, dazomet, and 1, 3-dichloropropene."

During the phaseout period between 1980 and 1991, Dutch growers maintained, and actually increased, production of horticultural crops that were once dependent on methyl bromide.

Successful crop production without methyl bromide in the Netherlands has been achieved "through research, adequate supplies of good-quality water, and available energy," Van Haasteren says. "Just as important has been our growers' ready access to high-priced product markets and their good management and technical skills."

In the Netherlands, about 8,000 growers produce 70 percent of the world's cut flower exports and 51 percent of world plant exports. Also, more than 3,500 nurseries produce 25 percent of the world's tree nursery stock, which includes pot- and container-grown plants, forest trees and shrubs, avenue and park trees, perennials, ornamentals, fruit trees and fruit tree rootstock, and rose culture and rootstock.

To wean themselves from methyl bromide, in the first step of the 10-year phaseout, Dutch growers reduced the amount of the fumigant needed by improving the method of application. They used sheets of gas-tight plastic to cover the soil in greenhouses, thereby decreasing the amount that escaped into the air and cutting the quantity needed.

In most cases, soil replacements such as rockwool, rock, clay and pumice granules, flexible polyurethane foam blocks, and coconut fibers are all being used as basic methods to replace methyl bromide for growing flowers, tomatoes, strawberries, cucumbers, peppers, and eggplants. With these soil replacements, there is no longer a danger of infestation by soilborne pests.

"Our growers report, on average, a 10- to 20-percent increase in cash income with these artificial substrates," Van Haasteren says. "We're primarily using biological controls for pests that don't require soil. But, control of secondary fungal or bacterial diseases that occur during the growing period may be necessary."

For growing strawberries without soil in greenhouses, the Netherlands developed a system of hanging the plants, which grow in peat blocks, to prevent contact with any soilborne diseases. Nutrient-enriched water is pumped to the plants, reducing plant wetness and related foliage pest problems. The wastewater from the roots is recaptured, sterilized, and reused.

"After investing in this system, growers significantly increase production and can harvest up to three crops each year," according to Van Haasteren.

In the Netherlands, a wide range of soilborne pests can be killed by sterilizing the soil with steam. Using natural gas to heat water, Dutch growers treat soil in greenhouses with steam. The high cost of energy and the inability of steam to penetrate deeply into the soil are limiting factors with this alternative to methyl bromide. In the Netherlands, however, industrial customers get volume discount prices. Permeable soil beds use anywhere from 2.5 to 5 cubic meters of natural gas per square meter of greenhouse area per year; less permeable soils can require as much as 8 cubic meters. Steam sterilization cannot be used in low permeable soils or those with a high peat content or a high soil-water table.

Van Haasteren says that the Netherlands has developed a way of surface-injecting steam under plastic sheets, then using negative pressure ventilation to draw the steam into ducts buried 50-70 cm below the soil surface, thus reducing the energy input. Of course, this requires a capital investment in a permanent duct/drain system under the greenhouse.

An economic advantage of steam sterilization in the Netherlands is that growers can replant immediately after the soil cools, in less than 5 days. With methyl bromide, growers had to wait 3 weeks.

Although growers are using metam sodium, dazomet, and 1, 3-dichloropropene, these chemical substitutes are less effective than methyl bromide and often less suitable for some crops and pests. The soil can adapt, pests become resistant to the pesticides, and some chemicals require long waiting periods for planting.

"Since a major economic part of our agriculture is produced in greenhouses, the alternative practices we've discussed were implemented fairly easily by our growers," Van Haasteren says. "We have many small farmers close to residential areas and our climate is cool, with limited sunlight. The increased product quality, easy access to domestic and world markets, high food and flower prices, and skilled growers were all to our advantage."

Dense concentration of independent growers in a small area allows them to share contracted services such as a good infrastructure for getting substrates, pest control advisors, and mobile sterilization equipment for plant beds.

"Although we have found no single alternative to methyl bromide, growing crops with soil-less substrates has proven to be very successful," Van Haasteren concludes.