|Photo: Soil Science at North Carolina State University.|
Up until the last half century, agricultural producers used a variety of cultural and biological controls in an attempt to manage crop pests. The use of pesticides to control weeds, insects, diseases, and other pests is now the predominant force in industrialized agriculture, enhancing the ability of a few workers to cultivate large areas. With the advent of pesticides, human and environmental health have become areas of concern, as has the disturbance of natural biological cycles and, from the energy aspect, the use of fossil fuels for pesticide manufacture and use. Recent technology has made pesticides generally safer and more energy-efficient. This article reviews the energy involved in pesticide production and use and various management alternatives for pest control.
In the United States, approximately 1.25 billion pounds of pesticides are used annually; nearly half are herbicides with the most used being glyphosate and atrazine (1). The use of pesticides also varies by crop group. The fruit and vegetable industry uses the largest amount on a per acre basis, but, because of their large area of cultivation, the feed and food grain crops lead by far in total use. Forages and pastures overall use the least per acre and in total (2).
Of the overall total energy used in agriculture, less than 15% is attributed to pesticides (3) with most crop acres being closer to 5%. Fertilizer (primarily nitrogen), followed by direct fuel consumption for field operations then irrigation and grain drying, represent the greatest amounts of energy use in U.S. agriculture production (4). Transportation on and off the farm also uses significant amounts of petroleum fuels. Even though total energy use in pesticide manufacture is small in comparison, it can require two to five times as much energy per pound as nitrogen fertilizer manufacture. More detailed information on pesticide use and comparative energies in agriculture can be found in the references (3, 4, 5).
Energy used in the manufacture of pesticides is affected by chemical composition, the methods of manufacture, and the fossil fuel and other resources used to manufacture them. Petroleum chemicals, such as ethylene, propylene, and methane, are the source of many pesticides. The heating, distillation, stirring, and drying processes in manufacture also use electricity, natural gas, steam, and additional petroleum sources. Secondary and tertiary energy consumption occurs in the construction and maintenance of the manufacturing plant and equipment, consumption and handling of raw materials, disposal of waste, and other operations. Details of these energies, calculations thereof, and cost-benefit analyses can be found in reference (6).
Table 1 contains a summary of estimated energy requirements for the manufacture of some selected pesticides on a per pound of active ingredient basis and on a per acre basis for a typical use rate. Although these are older products, they are still used. Unfortunately, because of patent and other rights, little information is available on the newer concentrated materials. The relatively new class of biopesticides use limited fuels in their makeup but do consume energy during overall manufacture and use. It should be noted that the values presented in Table 1 for older chemicals may be off by a factor of ±10%, and the somewhat newer products may vary by up to 50% from the true value. New efficiencies in manufacturing result in newer plants manufacturing older chemicals that may have lower actual energy consumption than presented here.
Because of different use rates, pesticides also vary in energy use per acre. The values given in Table 1 are typical use rates for one or more major crops during a growing season, but the reader should realize that rates vary based on pests, crop grown, field conditions, and method and type of application. In addition, some pesticides can be applied multiple times to the same crop in a given growing season.
Table 1. Estimated manufacturing energy inputs for various pesticides (BTUs/lb), typical application rates (lbs/A), and energy per unit area of use (BTUs/A) on an active ingredient basis.
|(x 1000)||(lbs/A)||(x 1000)|
To illustrate the interaction of energy in pesticide production and its integration in a cropping system, consider the major trend of using genetically engineered glyphosate-resistant crops. Glyphosate is the predominant herbicide used in the United States. On a per pound of active ingredient comparison, glyphosate requires nearly two and a half times the energy for manufacture (195,200 BTUs/lb) of atrazine (81,700 BTUs/lb) and about one and a half times that of metolachlor (118,700 BTUs/lb), two of the major herbicides that glyphosate has been replacing in corn production. However, both atrazine and metolachlor were, and are, used together for controlling broadleaf and grassy weeds in corn, whereas glyphosate alone controls these and often many other problem weeds if emerged at the time of application but with no residual activity as with the others. Glyphosate is also used at a lower volume rate per acre than the total of the two, resulting in a calculated energy use per acre for glyphosate of nearly 25% less than the two herbicides combined.
Several newer pesticides, particularly herbicides, are labeled for use at very low rates, literally a few ounces or less per acre. While documented energy use in manufacture is not specifically known, estimates would suggest, on a per pound basis, energy use is greater, but on a per acre basis energy use is likely to be two to three times less than their predecessors with higher use rates.
In addition to the energy for manufacturing the active ingredients of pesticides, energy utilized in formulation, packaging, and transportation can also represent sizable amounts of energy expended to convey usable pesticides to the end user. These amounts can vary significantly because of the variety of uses, formulations, and packaging options. A review by Green (6) suggests that emulsifiable oil-based pesticides may require about 8,600 BTUs/lb, wettable powders up to 12,900 BTUs/lb, granules 4,300 BTUs/lb, and microgranules 8,600 BTUs/lb for formulation. Packaging is estimated to require about 860 BTUs/lb, and transportation about 430 BTUs/lb. With some newer concentrated pesticides applied at very low rates per acre, energy expended on a per acre basis for formulation, packaging, and distribution will be significantly reduced.
Once the end user purchases a pesticide, it needs to be applied to the crop or target. When some pesticides are used, adjuvants must be added to the tank mixture for enhanced efficacy. Typical rates could be 1 to 2 qts/A. For broadcast application, a tractor or truck with a tank sprayer may require up to 0.5 gal/A of fuel or more. If application is combined as part of the field tillage or other operations, the extra energy expended is very low. Some specialized equipment, such as orchard sprayers, can consume significantly more fuel (1+ gal/A). Aerial spraying may also consume more energy than land applications if fields are small or odd-shaped and turning is frequent. Newer low-volume application technology can reduce energy use by lowering transport weight and travel to and from refill sites.
Use of low-volume/low–rate technologies and substitution of lower energy materials or non-petroleum-based pesticides can also lower overall energy expended in crop production.
IPM triangle courtesy of Royal Botanical Gardens Melbourne.
Although pesticides represent less than one-sixth of the energy used in the production of many crops and energy use per acre is decreasing, it is still valuable to evaluate alternative pest control measures to reduce energy expenditures.
The use of integrated pest management (IPM) is the first step in planning for pest control and, it is hoped, pesticide reduction. IPM involves scouting for pests and determining the economic thresholds of pests so as to reduce spraying preventative pesticides on a frequent and calendarized basis. In heavy use pesticide situations, such as for fruits and vegetables, a 50% or more reduction in pesticide use can often be realized from using IPM.
Other good crop management practices such as adequate fertility, crop rotations, cover crops, proper plant spacing, and optimal planting dates can also often reduce the amount of pesticide needed per acre.
Because herbicides are such a large part of overall pesticide use, there have been suggestions of using mechanical cultivation as a practice to reduce pesticide use and thus energy consumption. As an example, we can make such a comparison in the production of soybeans. It is a somewhat typical practice today to apply 1 qt/A of glyphosate in one postemergence operation to glyphosate-resistant soybean varieties. This requires a total of slightly more than 230,000 BTUs/A for all energy inputs from manufacture to application. Formerly mechanical cutlivation was used consisting of at least one rotary hoeing and two standard sweep or shovel cultivations to achieve sufficient weed control. These operations would require a total of approximately 192,000 BTUs/A direct diesel fuel equivalent, plus an estimated additional 38,000 BTUs/A for indirect energies associated with fuel acquisition and processing and farm equipment manufacture. As can be seen, the estimated energy totals for both methods of weed control are similar. Thus, the decision on which method to use is not so dependent on energy use but on weed control efficacy and other practical considerations, such as time, labor, weather, and, perhaps most important, overall economics and effect on the environment.
Genetic engineering has been providing new biological methods of pest control that can significantly reduce pesticide use. The incorporation of insect resistance into the germplasm of various crops has reduced the need for energy-intensive insecticides in corn, cotton, and several other major crops. Use of biopesticides will also reduce energy use if the volume and application methods do not consume excessive amounts of energy.
Although pesticides are energy intensive in their manufacture on a per weight basis, they represent much less than 15% of the total energy invested in the production of many field crops. The first step in reducing energy use in pest control is to practice IPM concepts on the farm. Because pest control is important both in yield and quality of crops, it is of utmost importance to first choose the best control methods, then evaluate methods to reduce total amounts of energy in the various processes. These practices will often provide significant reductions in per unit energy use of crop production compared to selecting a practice based solely on low fossil fuel energy that may sacrifice pest control.
When and where pesticides are used, choosing concentrated low-energy chemicals that are environmentally benign can provide savings and useful benefits.