BANNED in the USA
Methyl bromide will soon be gone. What are the alternatives? Methyl bromide has long been the pre-eminent chemical used for preplant fumigation. But it will be banned completely in 2005 and a phase-out period is currently in place. While no alternatives compare to the effectiveness of methyl bromide, their use will become widespread once the methyl bromide phase-out period ends. Site conditions (soil texture, moisture and temperature) and knowledge of pests that have historically been present at the site are key elements that will determine which alternative will work best. Knowing more about methyl bromide and the existing alternatives that will be used once the phase-out period is complete will help you make the right choice.
Methyl bromide (MeBr) is the predominant preplant soil fumigant used on more than 100 crops, including turfgrass. Although first reported as a soil fumigant in 1940, MeBr use in turf applications probably dates back to 1958 when it was used during the renovation of putting greens at the Greensboro, N.C., Country Club. Today, MeBr is commonly used as a "soil disinfectant" in golf course and athletic field construction and renovation, and on sod farms, especially those where warmseason turfgrasses such as hybrid bermudagrass, seashore paspalum, zoysiagrass and St. Augustinegrass are grown.
In turf applications, two methods of fumigation are employed: hot gas and solid tarp. Hot gas is typically used on small areas such as putting greens, while solid-tarp fumigation is used for large-scale applications such as sod fields, large putting greens, fairways and athletic fields. In solid-tarp application, MeBr is injected as a liquid, 8 to 12 inches into the soil, prior to planting. In a simultaneous process, a polyethylene tarpaulin cover is laid over the treated soil to retard dissipation of MeBr from the soil and to enhance its efficacy. In hot gas applications, a thin polyethylene drip tape is laid under a plastic tarpaulin and liquid MeBr is heated to produce a gas, which then diffuses through the drip tape under the tarpaulin and into the soil. Once MeBr is applied, it rapidly permeates the open soil pore spaces where it acts as the most effective material - capable of eliminating nearly all soil-borne pathogens including troublesome nematodes. MeBr is also extremely effective at killing plant propagules such as bermudagrass stolons and rhizomes, nutsedge tubers and most broadleaf and grassy weed seeds.
Fumigation is important for long-term success Fumigation is important because having weed-free sod and sprigs is paramount to a successful landscape, athletic field or golf course. This has been especially true in the bermudagrass market where off-type contamination is prevalent, and lawsuits over contaminated sod and sprigs are common. Further, as a result of these contaminants, many state sod and seed certification agencies are now requiring fumigation and inspection of sod fields before granting the growers a "certified" label. This is the result of an effort to limit legal skirmishes between the grower and the end-user.
Furthermore, many of the troublesome weeds found in turf do not have adequate control methods using standard pre- and postemergence herbicides. Likewise, only fenamiphos (Bayer's Nemacur) and ethoprop (Aventis' Chipco Mocap) remain labeled for golf course turf and fenamiphos is the only nematicide labeled for industrial grounds and cemetaries. There are no nematicides labeled for landscape or athletic turf. Therefore, control of these damaging pests before they are brought into the landscape is extremely important.
Methyl bromide banned - January 1, 2005 Although MeBr is the most effective fumigant, this odorless, colorless gas is being banned because of environmental concerns. Specifically, MeBr has been designated an ozone-depleting substance and, under the Montreal Protocol (an international treaty developed to protect the earth from the detrimental effects of ozone depletion), it must be banned. Ozone (O subscript 3) is an unstable, pale-blue gas that forms a layer within the stratosphere, extending to a height of 18 miles above the earth's surface. This layer absorbs much ultraviolet radiation and prevents some heat loss from the earth. The breakdown of ozone, however, allows more ultraviolet radiation to reach the earth's surface, thus increasing the risk of skin cancer and cataracts.
In 1992, the parties (representing over 160 countries) of the Montreal Protocol reviewed the environmental science on MeBr and listed it as an ozone-depleting substance. As a result, in 1995 the parties agreed to limit production at levels produced in 1991. At a subsequent meeting in 1995, the parties agreed to phase out production of MeBr in industrial nations, including the United States. The phase-out will commence with a 25 percent reduction in 1999, a 50 percent reduction in 2001 and a 70 percent reduction in 2003, followed by a complete ban in 2005. Restrictions in developing countries were less stringent, with a complete phase-out not occurring until 2015. Aggravating many in the United States, the more stringent U.S. Clean Air Act required an accelerated phase-out requiring a total ban by Jan. 1, 2001. In 1998, however, the first exception ever made to the Clean Air Act was passed by congress, delaying the phase-out until 2005.
Inconsistencies and uncertainties The MeBr issue has become the subject of debate and international controversy. The debate centers around the fact that scientists do not agree on how much MeBr actually contributes to ozone depletion. In a 1992 Science Assessment Report to the Montreal Protocol, it was reported that agricultural use of MeBr accounts for less than 3 percent of the threat to the ozone layer. In a similar report issued in 1994, it was indicated that the earth's ozone layer would return to normal by the middle of the next century, even if methyl bromide remains available to farmers. Since then, these estimates have been lowered even more; some say MeBr only accounts for 0.4 percent of the threat to ozone. The question of, "Where does the other 97 percent come from?" begs an answer when one considers the gravity of this ban. Scientists agree that most comes from less controllable sources like the oceans, forest fires and automobile emissions.
As MeBr prepares to take its place alongside some of the first banned ozone-depleting compounds such as Freon, and halons, a class of brominated organic compounds that were used as fire retardants, turfgrass managers are in a quandary about what to do. No equally effective, affordable fumigant replacement has been identified.
What makes a good soil fumigant? Because of the impending ban on MeBr, scientists have conducted research to identify alternatives for this highly effective, broad-spectrum soil fumigant. In looking for a replacement, realize that, unlike vegetable crops (which utilize most of the MeBr), turf systems are perennial. In turf, even with fumigation, nematodes, soil-borne fungi and insects will re-infest; therefore, fumigation for the control of these pests is not the primary concern (as it is with vegetables). Weeds (specifically common bermudagrass, off-type bermudagrass contaminates and nutsedge) are the primary focus of fumigation in turfgrass systems. Because of the perennial nature of turf, these perennial weeds are difficult to effectively control, thus necessitating an effective fumigant.
Research - how did the alternatives fare? In our research trials conducted at three locations in the Southeast United States, we identified no single material that performed as well as MeBr. Some combinations did provide a good level of control, but the spectrum of control was not equivalent to MeBr. The only exception was methyl iodide (MeI) which performed well against the weedy grasses, nutsedge species and broadleaf weeds.
MeI is not EPA registered; however, Tomen Agro of San Francisco, Calif. is currently seeking registration for use as a soil fumigant. They are researching various fumigant uses of mehtyl iodide with the hopes of receiving registrations by 2005.
Although dazomet (BASF's Basamid) and combination treatments with 1,3-dichloropropene (Dow AgroScience's Telone II) and chloropicrin (various trade names and manufacturers) provided a good level of control of weedy grass species, control of nutsedge species was less impressive. Additionally, sporadic control was observed in the tractor tire ruts and at the point where the rototiller overlapped between successive passes. Because this material requires thorough mixing with the soil, it is important for applicators to pay particularly close attention. Any failure to uniformly incorporate these products may produce undesirable results.
Metham sodium (UCB's Metam CLR, AmVac's Vapam and Wilbur Ellis' Soil Prep) and the various combination treatments (same as above) provided partial control of the weeds being evaluated. Specifically, the metham sodium co-applied with chloropicrin under a tarpaulin provided the best results. The costs associated with this treatment, however, are greater than that for MeBr. As with dazomet, sporadic control was noted and there was some variation between research trial locations that could be attributed to differences in soil texture. In addition, worker protection issues and personal protective equipment requirements for metham sodium application may make this use of the product impractical in extremely hot climates such as Florida.
Where does this leave us? Although no single alternative for all of the MeBr uses presently exist, a number of options are available. These include both chemical and non-chemical alternatives. However, because the fumigant market is small, it may be difficult for manufacturers to justify further research to find MeBr replacements that are equally effective.
Turf, due to its perennial nature, is being hit the hard by the ban. Even if an equally effective alternative were found today, registration would not produce a legal, usable product by the 2005 phase-out deadline. Fortunately, there are alternatives, although less effective, that the turfgrass industry can utilize for preplant fumigation.
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