March/April – 2004
Author: Christine Paul
With the impending worldwide ban on the use of methyl bromide, can hydroponic technology offer acceptable, solutions in temrs of both economic and environmentally friendly alternatives?
Until recently, methyl bromide – a highly effective fumigant used to control insects, nematodes, weeds, and pathogens in more than 100 crops, in forest andornamental nurseries, and in wood products – has been used on a large-scale worldwide for soil fumigation, post-harvest protection, and quarantine treatments.
In the US alone, for example, the Environmental Protection Agency (EPA) estimates that 13.3 million pounds of methyl bromide were used in Florida croplands between 1995 and 1996. In 1995, tomatoes were planted on approximately 40,000 acres of Florida farmland, and an estimated 94% of this acreage was treated with methyl bromide at a rate of 142.5 pounds per acre.
However, under the Montreal Protocol of 1991, methyl bromide has been defined as a chemical that contributes to the depletion of the Earth’s ozone layer. The bromines that it contains are 50 times more destructive to ozone than chlorine (e. g. from CFCs).
Additionally, it has been shown that people risk exposure to methyl bromide used in agriculture, which can result in harmful effects to the lungs, throat, eyes, skin, central nervous system and respiratory system. Fumigation exposure also leads to pain in the chest, nausea, dizziness, numbness, and weakness in the extremities. To date, at least 20 people have died in the US as a direct result of methyl bromide exposure.
Under the Montreal Protocol, the subsequent phase-out of methyl bromide was agreed to by 183 countries. The manufacture and importation of methyl bromide phase-out in developed countries is as follows:25% reduction in 1999, 25% reduction in 2001, 20% reduction in 2003, with complete phase out reached by 1 January 2005. In developing countries, consumption was frozen in 2002 at 1995-98 average levels, followed by a 20% reduction in 2005 and complete phase-out in 2015. Exemptions for both developed and developing countries include quarantine, critical uses, and certain pre-shipment uses.
According to model analysis, the loss of methyl bromide will have significant impacts on producers and consumers of crops that currently rely on it as a soil fumigant. Methyl bromide allows the US to remain competitive with Mexico, which relies upon the labour intensive, but relatively less expensive option, of hiring workers to pull weeds from planting beds.
Unless viable alternatives are found, it is feared US farmers and other users in developed countries will be at a disadvantage when competing with agricultural products produced in developing countries where methyl bromide will continue to be available for several years after the US phase-out.
In search of alternatives
According to the Agricultural Research Service (ARS), the research arm of the US Department of Agriculture (USDA), finding a viable solution for methyl bromide is proving no easy matter. “There is no single alternative fumigant, chemical, or technology that can readily substitute for methyl bromide in efficacy, low cost, ease of use, wide availability, worker safety, and environmental safety below the ozone layer, ” states one finding.
Research by the USDA indicates that multiple alternative control measures will be required to replace the many essential uses of methyl bromide.
Notwithstanding, a groundswell is occurring among many growers as well as scientists and researchers in support of finding workable, safe alternatives.
One such instance is that of Professor Rodrigo Rodriguez-Kabana from the Entomology and Plant Pathology, Auburn University in Alabama, US, who has reformulated a chemical used as the triggering agent in automobile airbags into an environmentally friendly pesticide replacement for methyl bromide. Professor Kabana has indicated that this could be available to the market, for a limited number of crops, as early as the 2004 growing season.
For pre-plant uses, alternative measures include combinations of fungicides, herbicides, and insecticides;other fumigants;and nonchemical alternatives, including changes in cropping systems, resistant crops, and biological control.
The Florida model
With the imminent loss of methyl bromide, overall total Florida tomato production is predicted to decrease 2.4% and total shipping point revenues are predicted to decrease $68.1 million According to a recent USDA report:”Mexican-produced tomatoes are expected to gain significant market share with shipping point revenues increasing by $51.5 million. Total US strawberry production is expected to decrease by 35.3%, with wholesale price increasing by 9.4% and Mexico gaining a minimum of 10% market share. Overall summary of model output indicates that if low impacts are realised (5 to 10% yield loss), then shipping point revenue losses of $179.5 million in Florida and $143.7 million in California can be expected. ” A small group of University of Florida scientists, in 1995, gathered to look at future alternatives to methyl bromide research efforts within the State. Additionally, their aim was to draft a long-term, five-year research project proposal for possible USDA-ARS funding. The USDA provided annual funding from 1996-2001 and this was used to initiate field-scale demonstration/validation studies at multiple sites within the major crop producing regions of Florida as well as to support small-plot field research trials at various locations across the State. In total, 54 projects, involving 21 University of Florida and USDA scientists, were separately funded during the five-year grant period.
Researchers investigated different substances and production systems to control weeds, pests, and diseases, predictably, with varying results. These included alternative fumigants, herbicides, biorationals, application techniques, resistant plants, solarisation, cover cropping, organic amendments, flooding, and crop rotation.
Results from the studies showed that regardless of alternative chemical or application method, pest control efficacy for all the fumigant alternatives is generally a little less than that of methyl bromide and more highly dependent upon uniform delivery and distribution.
Says University of Florida researcher, Joseph Noling:”Unlike methyl bromide, prevailing soil and climactic conditions before and after fumigant application are much more important determinants of efficacy and crop response with alternative chemicals”. It is also apparent that growers can cause significant crop response variability through inappropriate land preparation or substandard application procedures. ” Performance of fumigant and herbicide alternatives to methyl bromide, such as Telone products and chloropicrin, have been identified and studied under USDA/ARS-funded research. “However, the culmination of this research has also demonstrated that satisfactory yield responses probably can’t be consistently achieved in every field or in every season as equivalent to that of methyl bromide,” says Noling. “As a result, growers must learn to expect some disease, some loss, and recognise that some inconsistency is unavoidable. The biggest continuing challenge facing the scientific community in Florida is developing and improving alternatives, which further minimise the 5-10% impacts on yield for each of the methyl bromide-dependent crops.” Clearly, with the cut-off date for use of methyl bromide looming, time is running out, however, at this stage there has been no single technology breakthrough in the hunt for alternatives.
The case for hydroponics
According to a recent EPA report, Hydroponics and Soilless Cultures on Artificial Substrates as an Alternative to Methyl Bromide Soil Fumigation, the use of hydroponic technology can prove a viable alternative to methyl bromide soil fumigation for greenhouse grown tomatoes, strawberries, cucumbers, peppers, eggplants, and some flowers. “Hydroponics allows crop culturing without soil fumigation by providing a system where a majority of plant needs are met by mixing water soluble nutrients with water, and eliminating requirements for soil”. The advantages of hydroponic or soilless cultures on artificial substrates are:
– an absence of competing weeds, soilborne pests and toxic residues;
– water conservation (with recycling systems, hydroponic systems use one-tenth the amount of water used in irrigated agriculture);
– conditions that can be altered quickly to suit specific crops, various growth stages, and environmental/climate conditions.
Other benefits of hydroponics, as noted in the report, include:the system’s ability to bring fresh oxygen to the root zone and to take away “off-gases”;the facilitation of more efficient root systems;the ability to grow plants closer together than normally, thus producing more agricultural product per given area, while avoiding competition for scarce nutrients in the root zone.
Bob Hochmuth, a vegetable expert with the University of Florida’s Institute of Food and Agricultural Sciences, is a strong advocate of the use of hydroponics as a suitable alternative to methyl bromide, especially for high-value crops such as tomatoes, coloured bell peppers, cucumbers, Bibb lettuce, herbs and strawberries. “Soilless agriculture is not the wave of the future, it’s already here, ” he says. “It makes sense to move production of some high-value crops out of the soil altogether. In fact, some growers are desperately looking for alternatives to growing crops outdoors in disease-infested soils, and they’re turning to greenhouse production and soilless growing mediums, commonly known as hydroponics. All plant nutrients are supplied in the irrigation water. ” Currently, it is estimated that there are now more than 70 acres of crops under protective cover while more growers are looking at growing their crops outdoors in hydroponic systems.
According to Hochmuth, although hydroponics is a more expensive way to grow crops, there are many advantages, especially with crops like tomatoes and strawberries. “Growers can sell tomatoes for $2 to $3 per pound, and the cost of producing greenhouse hydroponic vegetables ranges from $2 to $15 per square foot, ” he said. “But those higher costs can be offset by higher production – up to 10 times higher than field-grown produce. ” Extended marketing seasons are another big advantage with greenhouse hydroponic crops. Also, because they are not subjected to the usual insect pests, weather conditions, and other types of damage, greenhouse crops have a better appearance generally, optimising both consumer appeal and higher prices for growers.
Hydroponic strawberry production
Strawberry growers worldwide fumigate the soil with methyl bromide before planting to control soilborne insect pests, diseases, and weeds. This fumigation is seen as essential to obtain high yields and high-quality fruit.
Recently, as reported in PH&G (Issue 69), strawberry plasticulture growers in both Florida and California, as well as the seven-state, south-eastern Strawberry Consortium, have applied to the US Environmental Protection Agency (EPA) for “Critical Use Exemption” to continue to use methyl bromide.
The consortium argues that despite massive amounts of money and time being spent to find a methyl bromide replacement, adequate alternatives have still not been identified for strawberry plasticulture growers in the south-east.
Fumiomi Takeda, an ARS horticulturist at Kearneysville, US, however, is taking a positive approach and investigating the use of hydroponics as a viable alternative to methyl bromide. “With the fast approaching ban on use of this chemical, growers are anxiously looking for alternatives. It is estimated that banning methyl bromide will cut in half the annual production of field-grown strawberries in California and Florida, our major producing states, ” he says. “But growing strawberries hydroponically eliminates the need for methyl bromide on this crop, ” he adds, During research trials of hydroponic production of strawberries, Takeda controlled the few foliage pests with natural agents. “Two-spotted spider mites, thrips, and powdery mildew were the major problems we encountered in our greenhouse production of strawberries. We used beneficial predatory mites to control the thrips and two-spotted mites. The mildew problem can be resolved by moderating the humidity level in the greenhouse and by growing varieties that resist mildew infection, ” he said.
Ripe fruit from hydroponically grown plants were harvested twice a week from December to May, the period when shipments of California strawberries slow down. Both fruit quality and taste were excellent. “Although initial set-up costs for hydroponic farming are high, growers may recoup that cost by producing a higher value product, increasing yields, and spending less money to control pests and diseases, ” says Takeda. “Our research demonstrated that two California strawberry varieties can be grown by soilless means. However, we need more research to measure the performance of other strawberry varieties and to investigate the influence of plant type – plug, fresh-dug, dormant, or single or multiple crown, as well as planting dates. ” In Dover, Hillsborough, US, University of Florida Extension Agent Eric Waldo, together with horticulturist John Duval, is working on a research and demonstration project to examine how well strawberries grow outdoors in bags filled with perlite and other inorganic growing media. “So far, the results have been encouraging, with higher yield from plants in bags of perlite than from regular soil-grown plants, ” says Waldo. “Essentially, what we’re doing is growing strawberries in an outdoor hydroponic system, supplying all the nutrients in irrigation water. The bags of perlite provide an inorganic growing medium for plant roots, but the perlite has no nutrients or any of the harmful organisms that typically infest regular soil. ” Balanced against the higher cost of using perlite bags, is the expense spared to the grower of costs associated with methyl bromide soil fumigation and herbicides for weed control.
In the Netherlands, formerly one of Europe’s largest users of methyl bromide for the fumigation of strawberries and many other crops, growers are successfully using hydroponic production, eliminating risk of infestation by soilborne pests, and at the same time increasing crop yield and quality. There are approximately 2,072 ha of strawberries grown in the Netherlands, with 1993 production of strawberries at roughly 31, 000 tonnes. Almost half of this total was from greenhouse production.
Peat bags are primarily used in the production of greenhouse strawberries and to cultivate new runners. To stimulate bud formation, young plants are exposed to short-day lighting and then placed in greenhouse substrates or outdoors to fruit. Alternatively, they are stored for up to eight months at -2°C in a dormant state awaiting flower development. During warmer weather, mature plants may produce strawberries within 60 days without the use of methyl bromide or any other type of soil fumigant.
The work that has been achieved in the phasing out of methyl bromide in the Netherlands and the alternatives developed, particularly in the hydroponic sphere, has not only allowed the development of a number of economic and environmental advantages, but also provides an important model for other countries to follow.
Economic viability of hydroponics
According to the EPA report, hydroponics is an economically viable alternative to methyl bromide fumigation for a number of crops, including strawberries and cucumbers (See Tables 1a and 1b). The report states the following: “Although materials and total costs are higher for hydroponic systems compared to methyl bromide fumigation, operating costs are generally lower (except for double crops of strawberries), and overall crop yields far exceed those obtained with methyl bromide. “In general, strawberry and cucurbit yields using artificial substrates are double those obtained using soil. In fact, production on one greenhouse acre is equivalent to that on six to ten field acres with long-term production costs being much lower (Rosselle, 1996). Adjusting costs ($/kg yield) to take into account crop yield, renders costs comparable to that of methyl bromide fumigation.
Furthermore, hydroponics costs are expected to decrease as sales continue to increase and these systems become more commercialised (Rossell USDA, 1996). ” Other cost advantages of hydroponics include a potentially fast and flexible hydroponic cropping period, which allows growers to quickly change production to take advantage of market conditions. Because of the short cropping period (four months total) and the development of cold storage techniques, growers can increase or decrease production depending on prices, or select alternative crops if crop prices are not favourable. Findings from the Methyl Bromide Task Force, 1995, indicated that by marketing produce when prices are at a premium, growers can pay off initial capital investments in as little as three years.
The EPA report also makes mention of the fact that Dutch growers have already reported a 10 to 20% increase in cash income with the use of these artificial substrates.
Another important advantage offered by hydroponic technology is that growers have the option of “double cropping” to produce two crops per year from one planting, unlike conventional crops. This effectively halves the cost of crop establishment.
In 1997, Australia imported 1, 031 tonnes of methyl bromide, largely from the US, Europe and Israel. More than half of this quantity (679 tonnes) was used primarily as a soil fumigant in horticultural indus-tries, with small quantities used for structural and durable commodity fumigation. The remaining 352 tonnes was use for quarantine and pre-shipment purposes, as recognised by the Australian Quarantine Inspection Service (AQIS) to prevent the introduction of new pests and diseases between regions within Australia.
Under the Commonwealth Ozone Protection Act 1989, importers of methyl bromide are required to hold a “Controlled Substances Licence”, which restricts the quantities that they can import. Reductions in the quantities of methyl bromide imported are to be implemented in line with the Montreal Protocol phase-out schedule.
Gratifyingly enough, according to the latest issue of the National Methyl Bromide Update, recent studies have shown that bromine levels in the stratosphere are beginning to decline due to international restrictions on methyl bromide and halon use.
These studies, by Dr Paul Fraser of CSIRO Atmospheric Research, have given an Australian perspective to the MB phase-out with results indicating a 25% reduction in the quantity of MB in the Melbourne atmosphere since1998, consistent with the reduction in emissions based on consumption data. This study shows that the effort by Australian industry and researchers to phase out this harmful product is making a difference!
As is the case in many other developed countries, Australia’s horticultural producers are under increasing pressure to supply clean, high quality food at competitive prices. However, unlike its US counterpart, for example, Australian horticulture remains largely characterised by small-scale independent growers. For many of these growers, trying to reconcile the growing demand for their produce with the necessity of phasing out methyl bromide, a chemical on which many have been dependent for almost 20 years, is creating a Catch-22 situation.
Within Australia’s diverse climatic environment, no individual chemical of the current range of alternative fumigants available, has similar, ‘across the board’ efficacy as that of methyl bromide.
In search of suitable alternatives, one Victorian grower, Vince Sorace, Secretary of the Victorian Strawberry Growers’ Association, has been trialling Telone C-35 over the last two years.
Telone C-35, a soil fumigant from Dow AgroSciences that is used against fungal diseases, weeds and nematodes in many horticultural crops, including strawberries, melons, vegetables, and cut flowers, does not deplete ozone. Telone C-35 is made up of two chemicals: telone, a nematicide, and chloropicrin, a fungicide.
In 2001, Mr Sorace first trialled the product on about 5% of his plantings. Results achieved were encouraging. “We trialled it on about 7,000 selva plants, using the label rates of 350 to 700 litres/hectare. It was a fair size trial. . . but I’d also read a lot of the literature – particularly on the Internet from the United States – and all the trials and farmer experiences were positive. “We saw no difference whatsoever between MB treatments in previous years and the Telone C-35,” says Mr Solace. “Production was good, as were weed and disease control – with no plant losses.” Alan Shanks from the Department of Primary Industries, Victoria, says that grower trials like these, together with research projects, have helped to identify both advantages and disadvantages of the main fumigant alternatives. It’s important for growers to at least trial the alternatives they are considering. They are different to methyl bromide, they react differently, and in some cases, are applied differently, so people need to become familiar with them. This will give them the confidence to shift.
The National Methyl Bromide Response Strategy
The past two years, in particular, have witnessed a major acceleration of government funding to research bodies in search of alternatives to methyl bromide.
Recently, the National Methyl Bromide Response Strategy was produced by the Methyl Bromide Consultative Group in consultation with government, chemical companies and industry representatives, to address the impact of the phase-out of methyl bromide on Australian horticulture, which may prove to be significantly more complex than that of other ozone depleting substances (such as CFCs).
In its Executive Summary, the strategy states:”Australian horticulture cannot rely on a ‘drop-in’ replacement to be developed by multi-national chemical companies as occurred during the CFC phase-out. Similarly, it should not be assumed that the current exemptions for quarantine and pre-shipment uses would be indefinite.” At this stage, it is critical that affected horticultural industries apply one of the most important lessons of Australia’s CFC phase-out experience;that a pro-active approach to the phase-out will avoid or minimise potential adverse impacts on crop production. This Strategy seeks to provide a framework to enable users to take a proactive approach to the phase-out of methyl bromide. ” The strategy divides alternative measures into short, mid and long-term approaches. Under the classification of ‘long-term’ are:Integrated Pest and Disease Management; crop rotation; the use of organic amendments and biological controls;plant breeding programs;soil steaming and other methods of soil heating, e.g. Ohmic heating;tissue culture;soilless culture;and hydroponics.
The following excerpt from the Strategy looks at hydroponic production in the light of an alternative to methyl bromide: “Overseas experience indicates that it is technically feasible to produce some crops, such as strawberry runners, tomatoes and cucurbits, using tissue culture techniques and hydroponics instead of soil. The trend overseas is towards protected cultivation/soilless culture as productivity increases and land previously fully utilised becomes available for other high value crops not dependent on methyl bromide. “In Victoria, there are many carnation growers that have switched completely to the use of scoria beds rather than soil, and have no need to use methyl bromide. The production of nuclear, foundation and mother stock runners for the strawberry industry is suited to production in artificial substrates. ”
Summary and conclusion
With the rapidly approaching deadline for the discontinuation of methyl bromide as a soil fumigant, the race is on to find suitable, environmentally friendly and cost-effective alternatives.
There is no one alternative for the uses of methyl bromide, however, there are several effective combinations of control tools, and in some cases, alternatives require some changes to production systems, or a combination of approaches to control pests.
Since no single technology is available, a likely replacement is an Integrated Pest Management approach involving a combination of preventative techniques and alternative control mechanisms. These options also include hydroponics.
Hydroponics technology is out of the soil and brings with it biological control and Integrated Pest Management strategies that efficiently produce high quality, safe food for consumer consumption without the use of harmful chemicals.
In the words of Marvin Brown, president of BBI Produce Inc, Dover, US, one of the country’s largest grower and shipper of fresh strawberries:”-with no viable replacement in sight, soilless alternatives deserve serious attention. Advancements in technology and growing techniques will undoubtedly increase our desire and ability to use alternative production methods that are both economical and ecologically acceptable to all. “