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DOWNSIZING
FALLOWING
BIOCHEMISTRY
Despite its well-known toxicity, methyl bromide is still used widely before vineyard planting for a variety of reasons. Grower anxiety, the demands of bankers and meager industry research and education are behind the continued reliance on the deadly chemical.
What is driving methyl bromide use in wine country has less to do with soil science than with the perceptions of financial institutions. Worried about their investments in extremely expensive Sonoma and Napa vineyard land, bankers often demand that growers use methyl bromide as a form of insurance.
This allows bankers, not soil scientists, to set pest-control policy. And it ignores a good-sized menu of promising alternatives to methyl bromide, ignorance fostered by a dearth of industry-sponsored research and grower education.
An effort to compile available information and report on alternatives has been undertaken by the Methyl Bromide Technical Options Committee (MBTOC), which is sponsored by the United Nations for the 144-nation treaty governing chemicals that deplete the ozone layer. This international committee of experts has researched and reported on alternatives to methyl bromide since 1993 -- soon after it was recognized as destructive to the earth's protective ozone layer.
MBTOC reports that fully 75% of global methyl bromide use could be eliminated as soon as the year 2001 and replaced with a balanced blend of strategies. These include minimizing or not using methyl bromide at all, and applying integrated pest management strategies which include fallowing and some promising biochemical alternatives. MBTOC most recent report is available on the internet at http://www.teap.org. A U.S. EPA web site for alternatives to methyl bromide can be reached at http://www.epa.gov/spdpublc/mbr/infclear.html.
DOWNSIZING
The simplest and perhaps best alternative for wine grape country is to not use methyl bromide unless recourse to it is justified by the severity of the problem. Unfortunately, the need for methyl bromide is usually not adequately investigated in advance of its use. The presence of pests should be thoroughly monitored through tests of soil samples, but very often careful study is not exercised.
"More widespread use of such monitoring methods will pinpoint more precisely if and when pest populations are at levels requiring treatment, reduce unnecessary treatments of any type, and increase use of spot treatments rather than broad-scale applications over entire crops," stated MBTOC in its 1994 report.
Some viticulturalists who no longer fumigate with methyl bromide cite several factors that led to their decision -- such as its expense and their unwillingness to contribute to ozone depletion or endanger the health of themselves, workers and neighbors. Most important to their bottom line, however, may be that its economic benefits are marginal at best. Methyl bromide simply is not effective enough in many areas of Sonoma and Napa wine country to justify its cost of $1200 to $1400 per acre. For this report CATs interviewed several viticulturalists and found some who have given up methyl bromide and others who still use it because it is demanded of them and not because they believe it is beneficial. What's more, we learned that conditions in Sonoma and Napa seem to actually inhibit the effectiveness of methyl bromide soil fumigations.
Although famous for its ability to penetrate through matter and reach pests at lethal doses, methyl bromide does not penetrate far in heavy soils -- and in many areas of Sonoma and Napa wine country soils range from heavy to heavier. Nor does methyl bromide penetrate well into green woody matter such as the roots of trees and vines infested with oak root fungus -- the main target of its use in Sonoma and Napa wine country.
Research has shown that oak root fungus and another destructive vineyard soil pest -- tiny, almost invisible nematodes -- can rebound rapidly after fumigation, making any advantage gained actually very short-lived. Most growers who turn away from methyl bromide say their own experience has shown that its supposed benefits are largely hype.
In neighboring Mendocino County, Agricultural Commissioner Dave Bengsten, who has observed vineyard and orchard fumigations for years, says: "A large part of oak and vine roots reach down deep in the soil beyond the penetration of methyl bromide and roots which are within the fumigation zone aren't killed for the most part because methyl bromide doesn't effectively penetrate woody matter or damp soil around the roots."
"Oak root fungus is killed where the methyl bromide can reach, but too often the fungus grows back up the root again later, wiping out any positive effects of the fumigation," according to Bengsten. Barry Sloane, vineyard consultant to the Benzinger Family Vineyard, concurs. After years of observing his own and other methyl bromide fumigations, Sloane decided it isn't worth the effort or expense. Today the Benzingers do not fumigate any of their vineyards with methyl bromide, although they once thought it was necessary.
"Over time and with careful observation, we decided that methyl bromide was not accomplishing anything especially valuable. It doesn't seem to reach far enough into the soil to kill the most important pests. We've stopped using methyl bromide and will continue to plant -- and grow successfully -- without fumigating our soil" says Sloane. Several growers who asked not to be identified "because of the controversy" told us that it's smarter not to fumigate and risk losing a few plants since they can be replaced without great expense.
"It doesn't make sense to use such a destructive chemical when all you're really going to do is break even at best," said one vineyard manager.
Rather than using a biocide such as methyl bromide which kills soil organisms indiscriminately, growers can achieve greater long term success by building soil health and carefully developing integrated pest management strategies which combine several methods of pest control to reduce the impact of soil pests on newly planted vines to a level that doesn't impact future harvests.
FALLOWING
Fallowing -- or leaving fields uncultivated -- can be effective, although it can be costly for growers who need grape harvests to quickly start paying back expensive loans.
One or two years of fallowing could effectively reduce high pest populations if combined with soil amendments such as biologically active compost or the addition of various nutrients. Growing and plowing under speciality cover crops which will not support pest populations or which are antagonistic to pests could also be incorporated into an integrated strategy which involves limited fallowing. Although fallowing for several years running may not be affordable for most growers, it also may not be necessary except in extreme cases involving land that is only marginally useful for vineyard production.
"There is a change taking place as many 'fumigators' are now having second thoughts about this practice," says Domain Chandon vineyard manager Zack Berkowitz. "On our vineyards we have taken the approach of leaving blocks fallow for at least a year and up to 5 years rather than fumigate. Fumigation is expensive, not that effective and can be damaging to the soil."
BIOCHEMISTRY
Even if it did provide successful pest control, methyl bromide also kills beneficial soil organisms which are important to plant vigor or are in some cases hostile to soil pests. For example, when mycorrhizal fungi essential to the development of vigorous root systems -- that is, 'good' organisms -- are destroyed by methyl bromide, plants can be stunted. And there is evidence that some helpful soil fungi may be able to overcome and kill the problematic oak root fungus if encouraged to thrive rather than destroyed during fumigation.
In research where methyl bromide fumigation was observed to weaken but not kill oak root fungus, naturally occurring soil borne fungi in the genus Trichoderma eventually completed the job. Various species of Trichoderma are commercially available for agricultural use. According to William Quarles of the Bio-Integral Research Center in Berkeley, Trichoderma would be most effective in moist, slightly acidic clay loam soils containing adequate amounts of iron -- the soil profile of much of Sonoma and Napa. Quarles believes it would be worth investigating how to harness this natural biological enemy of oak root fungus.
Growers say they would be less inclined toward the take-no-prisoners approach of methyl bromide fumigations if they knew just where oak root fungus and nematodes were hidden in their soil. While tests are available to identify the extent of nematode populations, a sure and easy test for the presence of oak root fungus has yet to be developed. For oak root fungus the most important step is careful and thorough removal of roots left in the soil.
For nematodes -- and perhaps for fungi -- one promising new control has been mentioned as a replacement for methyl bromide. John Slaughter of Fowler, California, chose the soil amendment Oxycom-AG (manufactured by Soil Basics) which contains an organic peroxygen compound called ethaneperoxoic acid when tests of a field that had supported a vineyard for 70 years revealed advanced populations of root knot nematodes.
Although Oxycom-AG eliminates beneficial organisms along with the pests in a manner similar to methyl bromide, its negative effects can be offset through use of a specially designed soil innoculent. This, unlike after methyl bromide use, can be applied within days of treatment, and the innoculent quickly repopulates the soil with carefully chosen organisms.
Initial tests of Slaughter's vineyard showed that it was teeming with root knot nematodes, but he disdained the use of methyl bromide, instead removing the old vines, installing a drip system and using it to irrigate the soil with Oxycom-AG.
The result? In 40 post-application soil samples no root knot nematodes were found. Although there are no easy answers to replacing methyl bromide for pre-plant soil fumigations, carefully planning and well-designed and executed strategies could eliminate the need for methyl bromide.
Most important, growers need to join together to support research and education for alternatives to this chemical. When it comes to replacing dangerous pesticides such as methyl bromide, the reluctance to work together must be overcome and a spirit of cooperation defined as the new standard in Sonoma and Napa wine country.
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