Introduction and Statement of the Issue:
Throughout the agricultural era, the necessity of some type of pest control has become apparent. Current agriculture, especially agribusiness, relies heavily on chemical insecticides, fungicides, and herbicides to increase productivity and decrease disease and natural toxins in food production on a large scale. However, awareness has been raised by such groups as public health officials, environmentalists and concerned parents regarding adverse side effects of these chemicals, including environmental degradation, and human, plant and animal toxicity.
An agricultural subset, organic farming , has developed to voluntarily combat the chemical industry by utilizing natural, non-toxic and environmentally friendly forms of pest control. Unfortunately, very few herbicide alternatives have been developed, and fewer still that provide the same productivity and economic advantages of chemical herbicides, thereby resulting in a competitive disadvantage of organic farmers. The importance of investigation of alternative methods has become apparent, however, and this paper will analyze the benefits of a very innovative proposal, the use of pure steam as a post-emergent herbicide.
Aqua Heat Technology, Inc. has developed a non-specific vegetation control system capable of using pure steam to melt the waxy coating of plant foliage, thereby preventing the plant from retaining moisture and resulting in severe dehydration (Aqua Heat 1994). The system was initially designed for orchards and citrus groves. The most prevalent orchard design consists of a completely weed free strip approximately 6 feet wide under the trees (Marini 1997), with a mowed sod strip approximately 20 feet wide between the rows (Schupp and McCue 1996). The steam-based system would be used in place of chemical herbicides such as paraquat, simazine, diuron, and terbacil to remove weeds in the section under the trees (Marini 1997). The machinery, which is shown on the previous page, consists of a water tank, holding approximately 400 gallons of water, and a diesel-powered heat exchanger. The system is placed on a trailer and pulled by a tractor. The water from the tank, initially unheated, is passed through the heat exchange coils and heated to the boiling point. The water is then sprayed at low pressure, approximately 15 gallons per minute, through a series of nozzles extending to the side of the tractor. The nozzles are at close proximity to the ground, in order to avoid cooling of the steam, and are followed by a heavy, rubberized tarp dragged behind. The tarp is several feet long and is used to retain the heat for several seconds (Burgard 1996).
Other applications of this system have been proposed in the areas of pest and disease control. For instance, using the Aqua Heat machinery at the appropriate times can help break the life cycles of pathogenic fungi and insects that survive the winter in the leaf litter on the orchard floor. For instance, the effect of steaming apple maggot pupae, tentiform leafminer, and apple scab spores are all currently being studied with promising results. In addition, Aqua Heat is effective in killing cover crops, end-of-the-season vegetation, and weeds in row and vegetable crops (Burgard 1996). A smaller system has also been developed that can be used on curbs and roadsides, parks, gardens, golf courses, and athletic fields (Aqua Heat 1994). This analysis will primarily concentrate on using the steam based vegetation control system in orchards due to its increased progress; however, arguments in favor of such applications are also applicable to other usage options.
In order to fully assess the benefits and drawbacks of Aqua Heat, the advantages and disadvantages of current herbicides must first be considered. The use of herbicides for weed control is beneficial for both the farmer and the consumer. Innovations in herbicides and application machinery have allowed the farmer to perform large scale weed control with less intense manual labor. The former method of weeding involved tilling to dislodge and sever weed roots, which in addition to being extremely hard manual labor, also exposes soil, reducing moisture content and inhibiting water and air movement by destroying valuable macro and mircropore spaces. Tilling also increases erosion by removing all vegetation (Wrubel 1994).
Chemical herbicides have also drastically lowered food costs while increasing productivity, availability and abundance of food. In the past 50 years, food cost in the United States has decreased from 24% of the disposable income to 14%, largely due to the development of agricultural chemicals. Concerning production, the elimination of fungicides alone could possibly result in 80% to 100% losses of vegetable crops. The boost of agriculture is also reflected in the employment and the economy, and the elimination of agricultural chemicals could result in a reduction of $14.4 billion in the economy (Clark 1991). In addition, herbicides and other pesticides aid in the prevention of natural toxins and diseases. For instance, microorganisms are responsible for up to 6 million cases of illness and over 9000 deaths in the United States per year, such as Salmonella poisoning and Listeria. Also, plants themselves produce natural toxins, which account for 99.99% of all pesticides that we consume (Brackett 1991). Finally, many stringent state and federal legislation has lowered risks associated with pesticide use, (see EPA Office of Pesticide Programs).
In orchards specifically, herbicides increase tree growth, yield and fruit size as well as eliminate pathogens that can be transferred by nematodes from broad leaf weeds to the trees. In addition, many weeds, such as fescue grasses, are strong competitors for water and nutrients. Weeds also provide shelter for many rodents such as mice that feed on bark and roots, exposing and weakening the trees (Marini 1997). The necessity of weed control has now become apparent; however, the disadvantages of chemical methods and the analysis of the steam alternative still need to be considered.
Risks of Chemical Herbicide
Use
The health and environmental risks of chemical herbicide risk have become all too apparent in recent years. Herbicides are subject to leaching, resulting in surface and groundwater contamination. Studies have shown the presence of herbicides in drinking water, (Tap Water Blues: Herbicides in Drinking Water), raising questions of toxicity to humans and especially children. Although abundant research has been conducted concerning pesticides, especially DDT and DDE, much of herbicide toxicity, including neurological, immunological, developmental and reproductive effects due to even low level chronic exposure are as yet unknown (Wrubel 1994). However, many pesticide, including herbicide, related illnesses have been reported in relation to agricultural workers. The annual incidence of just physician reported cases in California alone is 1000 to 1500 (Maizlish, Rudolph and Dervin 1995). In addition, from a more moral standpoint, herbicide and pesticide toxicity testing is done largely on live animals including mice, rats, rabbits, sheep, dogs and monkeys (EPA 1988) posing severe threats to animal rights activists.
Several risks are associated with the four herbicides Aqua Heat would potentially replace, simazine, diuron, terbacil, and paraquat,. Simazine is a moderate eye and dermal irritant with unknown chronic effects or oncogenic, teratogenic and mutagenic potentials. Diuron is structurally related to linuron, which has indicated oncogenic threats in rats. In the past, fish kills, crop injury and vomiting, dizziness and diarrhea of workers were results of improper application methods. Terbacil is an irritant to skin, eyes and mucous membranes, and 50 % of the concentration remains in top soil 5-7 months after application (Tomlin 1994). Paraquat, one of the Dirty Dozen Pesticides as ranked by the Pesticide Action Network of North America, is an extremely toxic chemical through oral, dermal and inhalation exposure.
Weed resistance has become a serious threat to the productivity of chemical herbicides as shown by the article, The Invincibility of Herbicides?, by Bob Hartzler of the Iowa State University Extension. In fact, an annual ryegrass, Lolium rigidum, in Australia is allegedly completely resistant to the world's most popular herbicide, gyphosate or Roundup (Anderson 1996). The evolutionary herbicidal resistance of weeds could pose a serious threat to not only the herbicide industry, but also to farmers if no alternative techniques are available. Finally, herbicides, especially non- selective herbicides, also have the potential through drifting and other accidental contamination, to damage natural plant communities by harming sensitive species and altering the community structure (Breeze, Thomas and Butler 1992).
Benefits of Aqua Heat
The first and foremost benefit of the use of the Aqua Heat system for vegetation control is the gain of the benefits of herbicide use, with the simultaneous elimination of the risks and discussed problems associated with such chemical herbicide use. The Aqua Heat machinery only applies pure steam to the ground, and as known, water is abundant in every aspect of the environment. In addition, the non-specificity of the system enables a large area of coverage, as opposed to many chemical herbicides, which are often specific to certain types of weeds. However, the system has been shown to have no adverse effect on the trees themselves, because the temperature decreases drastically below the soil surface. At only 1 inch below the soil surface, the temperature has been measured to be less than 120 degrees, and at 2 inches the temperature does not change at all (Burgard 1996).
Aqua Heat's results are also fairly immediate, with weeds becoming withered and brown within 24 to 48 hours. Aqua Heat is also easier to use than chemical herbicides, with no necessary protective equipment for operators, no disposal or associated chemicals and containers, no federal or state restrictions on use, nor insurance required for chemical liability. In addition, Aqua Heat can also be used under any types of weather conditions, as opposed to many sprayed chemical herbicides (Aqua Heat 1994).
Economically, Aqua Heat is also competitive. The unit can be towed with common tractors, while the actual system would cost approximately $16,000 (Burgard 1996). The estimated cost per application for a Florida citrus grove is approximately $15-20 per acre, which includes the depreciation of the sprayer and the cost of the diesel fuel (Aqua Heat 1994). In comparison, the cost of chemical herbicides, such as a paraquat combination, is approximately $70 per acre (Marini 1997).
Disadvantages of Aqua Heat
Several uncertainties and disadvantages have also become apparent in studying the Aqua Heat vegetation control system. The major disadvantage is the demand for water. Approximately 2000 gallons of water is necessary to treat one acre of semi-dwarf trees; however, the tank capacity is only 400 gallons. Therefore, frequent water refills are necessary, resulting in increased time and costs that may not have been included in the cost estimate shown above. This can be an extremely large problem when a water source is not in near proximity, as is often the case. In addition, the tarp inhibits movement between the trees. Progress is being made on a swing arm and the use of a hot foam instead of water, which would help elevate both water demand and maneuverability problems. At the present, however, no current system is available. In addition, since Aqua Heat is only applicable to emergent vegetation, it must be applied at least three times a year, again increasing time and cost (Burgard 1996). Finally, not enough data is as yet available on the Aqua Heat system and an empirical comparison with current vegetation control techniques. Without professional publication, it becomes very difficult to gain trust in the agricultural community, or any professional community for that matter.
Summary Statement
Despite the obvious shortcomings of the Aqua Heat system, I think it is a very innovational and potentially beneficial system, worth consideration and future research. As shown by the advantages of weed control, some sort of herbicidal method is necessary in order to retain the productivity and efficiency of the current agricultural industry. However, the environmental and health-related risks associated with chemical herbicides are too severe and too uncertain to continue to be part of a sustainable agricultural system. More benign alternatives are necessary, and Aqua Heat has the potential to become a strong contributor to a more environmentally friendly movement. As shown by the existent research improvements, the main disadvantages of Aqua Heat are already being combated. Aqua Heat already has the capacity to be a sincere consideration for many small organic farmers. I feel the time frame required for the entrance of Aqua Heat into the main stream agricultural market is within a decade, and most definitely within two.