and may reflect regional and weather variations. Continuous wheat showed the lowest percentage of wheat acres treated with herbicides, but this may be due to the agroclimatic conditions in the region where this pattern predominates. Insecticide use. Insecticide use on continuous corn occurred much more frequently than on corn in rotations (table 4.3.1). Higher use of insecticides on continuous corn is needed to reduce the build up of insects, especially corn rootworm, which monoculture tends to encourage. Alternating crops with corn reduces the need for insecticide treatment because rootworms and other populations are not allowed to build up. Three-fourth of cotton acres were treated with insecticide, with little difference among patterns in average amount applied. Soybeans usually are not treated with insecticide. While only a small part of wheat acreage was treated with insecticides, the proportion of continuous wheat treated was higher than that for wheat in various rotations. Fertilizer use. Most corn, cotton, and wheat acres received nitrogen fertilizer in 1995, with smaller proportions receiving phosphate and potash (table 4.3.1). Cropping patterns generally did not influence average annual pounds applied except nitrogen use was higher for continuous corn than for some rotations, and lower for continuous cotton than for some rotations. Factors Affecting Cropping Patterns The primary factor determining a farmer's choice of cropping pattern is the rate of return; other contributing factors include agroclimatic conditions, farm programs, conservation programs, and environmental regulations. Crop rotations, generally, will prevail over monoculture only if more profitable as in Iowa, where corn-soybeans-corn was shown to yield $40 per acre more than continuous corn (Duffy, 1996). Climate, rainfall, environmental, and economic conditions divide the United States into very distinct agroclimatic regions, with each region's conditions determining its needs and ability to rotate crops. For example, the level and the variability of rainfall in a given area determine the usefulness of legumes in a rotation. Alfalfa and other deep-rooted legumes can deplete the subsoil moisture to a greater depth than corn. As a result, in arid and semi-arid regions and in subhumid and humid regions during drought, the inclusion of these legumes in a rotation may reduce the yields of the following corn or other crops. Under irrigated conditions or in areas of abundant rainfall, however, legumes in rotation with cash grains will boost yield and reduce the need for fertilizer by providing for some or all of the nitrogen needed by corn or small grains (National Research Council, 1989). Federal policies often unintentionally discourage the adoption of crop rotations. For example, commodity programs that restricted base acreage to one or two crops encouraged monoculture. To reduce this unintended effect, the 1990 Farm Act eliminated deficiency payments on 15 percent of participating crop base acres known as Normal Flex Acreage (NFA), regardless of the crops planted on them (with a few fruit and vegetable exceptions). As a result, many farmers flexed out of monoculture or idled the marginal acreage. The extent of flexing out varied by type of crop base, depending on expected relative market return. For example, oats appeared to be the least profitable program crop during 1991-94 as almost half of its NFA was flexed to another crop. The 1996 Farm Act allows 100 percent flexing (again with a few fruit and vegetable exceptions). Under the 1985 and subsequent farm acts, highly erodible land (HEL) used for crops requires a conservation plan to qualify for USDA farm program benefits (see chapter 6.4, Conservation Compliance, for more detail). Planting crops in rotation can reduce erosion and is a part of many conservation plans for HEL. Indeed, more HEL in corn in 1995 was in rotation (18 percent) than was non-HEL (12 percent) (table 4.3.2). Also more winter, spring, and durum wheat (50, 64, and 46 percent respectively) on HEL was in a fallow or idle rotation than non-HEL (34, 20, and 44 percent). Author: Mohinder Gill, (202) 219-0447 [mgill@econ.ag.gov]. Contributor: Renata Penn. References Brust, G.E., and B.R. Stinner (1991). "Crop Rotation for Insect, Plant Pathogen, and Weed Control", CRP Handbook of Pest Management in Agriculture, Editor David Pimentel, Second Edition, Volume 1. CRC Press Inc. pp.217-230. National Research Council (1989). Alternative Agriculture, National Academy Press, Washington D.C. pp. 135-150. U.S. Department of Agriculture, Economic Research Service (1991). Agricultural Resources: Situation and Outlook Report, AR-24. pp.39-46. Daberkow, Stan. G., Jim Langley, and E. Douglas Beach (1995). "Farmers' Use of Flex Acres", Choices, The Magazine of Food, Farm, and Resource Issues. Table 4.3.2-Cropping patterns on highly and non-highly erodible land in major producing States, 1995 n/a = not applicable. Id = insufficient data. Percentages may not add to 100 due to rounding. 1 2 For the States included, see "Cropping Practices Survey" in the appendix. Includes double-cropped with wheat or soybeans. Source: USDA, ERS, Cropping Practices Survey data. Zulauf, Carl, and Luther Tweeten (1996). "The Post-Com- Conversation with Michael Duffy (Sept. 30.1996). Depart- Heichel, G.H (1987). Legumes as a source of nitrogen in conservation tillage system. pp 29-35 in The Role of Legumes in Conservation Tillage System, J.F. Power, ed. Ankeny, Iowa: Soil Conservation Society of America. Power, J.F (1987). Legumes:" Their Potential role in agricultural production", American Journal of Alternative Agriculture 2(2): 69-73. PRODUCTION MANAGEMENT 4.4. Pest Management Insects, disease, and weeds cause significant yield and During the early 1990's, USDA's Economic Research Service (ERS), using a producer probability survey representing over 60 percent of U.S. crop production, began compiling a baseline on the uses of various chemical, cultural, and biological practices to control pests. According to these data, pesticides are used on the majority of crop acreage of most major commodities. Most growers also used scouting, economic thresholds, and other pesticide-efficiency techniques, but less than half reported the use of cultural and biological techniques. (For information on pesticide quantitities and active ingredients, see chapter 3.2, Pesticides.) The National Research Council recently concluded Why Manage Pests? Approximately 600 species of insects, 1,800 plant Cultural and biological techniques were the primary methods used to manage pests in agriculture for thousands of years. U.S. farmers began shifting to chemical methods upon the successful use of a natural arsenic compound to control Colorado potato beetles in 1867 (National Academy of Sciences, 1995) and the inception of USDA's chemical research program in 1881 (Klassen and Schwartz, 1991). The increases in crop yields throughout this century have been partly credited to pesticide technology; the majority of U.S. crop acreage is now treated with pesticides. The benefits of pesticides, the value of production that would be lost if alternatives were less effective, and the additional pest management costs if alternatives were more expensive have been shown in numerous studies (Osteen, 1987). The costs of pesticide use to human health and the environment have been much more difficult to quantify. A preliminary Cornell study estimates that the costs from human pesticide poisonings, reduction of fish and wildlife populations, livestock losses, honey bee losses, destruction of beneficial insects, pesticide resistance, and other pesticide effects are $8 billion annually in the U.S. (Pimentel and others, 1992). An alternative method that is more expensive or less effective than pesticides might be economically justified when weighed against the indirect costs of pesticides (see box, "Why Reduce Reliance on Pesticides?"). Pest Management Systems and Practices USDA cropping practices and chemical use surveys between 1990 and 1995 provide information about chemical, cultural, and biological pest management systems for five major field crops (corn, soybeans, wheat, cotton, and potatoes) and selected fruits and vegetables. About 60 percent of U.S. cropland planted to crops was represented in these annual surveys. Pesticide-Based Management Pesticides are applied annually to the majority of U.S. crop acreage. One or more pesticides are used to control weeds and other pests of major field crops, corn, soybeans, wheat, cotton, and potatoes (table 4.4.1), as well as most fruit and vegetable crops (table 4.4.2). Corn. The largest crop in the United States is corn, and it exceeds any other crop in the number of acres treated with pesticides (table 4.4.1). At least some herbicide was applied to 98 percent of the corn area in the 10 surveyed States in 1995, up from 95 percent in 1990. While the total amount of herbicide applied per acre fell slightly, the number of herbicide treatments and number of different ingredients applied per acre increased. The use of more frequent treatments and additional ingredients reflects an increase in the number of treatments later in the growing season and the grower's need for more broad-spectrum weed control. Treatments applied later in the growing season are less likely to run off or leach and are more likely to be post-emergence herbicides, which are often less persistent in the environment. The amount of herbicide applied per acre has fallen with the increased use of low-rate sulfonylurea herbicides and with reduced-rate applications of atrazine and other older herbicides. Less than one-fourth of the corn acreage received insecticides in 1995, and corn rootworm was the most frequently treated insect. Insecticide applied to the soil before or during planting kills hatching rootworm larvae and is a common control method, especially when corn is planted every year. Corn acreage treated with insecticides in 1995 was down 6 percentage points from 1990. This decline may be due to closer monitoring of insect and mite populations in the previous crop to decide if preventive treatments are needed. Soybeans. Herbicides account for virtually all the pesticides used on the soybean crop. In the late 1980's, sulfonylurea and imidazolinone herbicides, which could be applied at less than an ounce per acre, began to replace older products commonly applied at 1 to 2 pounds per acre. They are now among the most commonly used soybean herbicides and have caused total herbicide use to drop. However, the number of acres treated and number of treatments per acre have increased, partly due to the growth in no-till soybean systems, which often replace tillage prior to planting with a preplant "burndown" herbicide to kill existing vegetation. The area treated with herbicides after planting increased from 52 percent to 74 percent from 1990 to 1995, while treatments before planting dropped only a few percentage points. Wheat. Wheat is one of the largest field crops in the United States, in terms of acreage, and is the least pesticide-intensive. Wheat accounted for 29 percent of the surveyed acreage in 1994, but received only 4 percent of the pesticides. Herbicides were applied on about half of the winter wheat, the largest wheat crop, in 1995, up from only 34 percent in 1990. Winter wheat grows through the fall and winter, and many weeds germinating in the spring cannot compete with the established wheat. In contrast, spring wheat seedlings compete directly with weed seedlings in the spring, and nearly all of these crops receive herbicide treatments. Why Reduce Reliance on Pesticides? Concern about the side effects of synthetic pesticides began emerging in scientific and agricultural communities in the late 1940's, after problems with insect resistance to DDT. The public became concerned about the unintentional effects of pesticide use after Rachel Carson's book on bioaccumulation and other potential hazards was published in the 1960's. Many unintentional effects of pesticide exposure on nontarget species have been reported since then, including acute pesticide poisonings of humans (especially during occupational exposure) and damage to fish and wildlife, including species that are beneficial in agricultural ecosystems. Since the 1960's, some pesticides have been banned, others restricted in use, and others' formulations changed to lessen undesirable effects. Human Health Impacts. The American Association of Poison Control Centers estimates that approximately 67,000 nonfatal acute pesticide poisonings occur annually in the United States (Litovitz and others, 1990). However, the extent of chronic health illness resulting from pesticide exposure is much less documented. Epidemiological studies of cancer suggest that farmers in many countries, including the United States, have higher rates than the general population for Hodgkin's disease, leukemia, multiple myeloma, non-Hodgkin's lymphoma, and cancers of the lip, stomach, prostate, skin, brain, and connective tissue (Alavanja and others, 1996). Emerging case reports and experimental studies suggest that noncancer illnesses of the nervous, renal, respiratory, reproductive, and endocrine systems may be influenced by pesticide exposure. Case studies, for example, indicate that pesticide exposure is a risk factor for several neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis, also known as Lou Gehrig's disease (Alavanja and others, 1993). A comprehensive Federal research project on the impacts of occupational pesticide exposure on rates of cancer, neurodegenerative disease, and other illnesses was begun about 4 years ago in North Carolina and Iowa; about 49,000 farmers who apply pesticides and 20,000 of their spouses, along with 7,000 commercial pesticide applicators, are expected to participate in the study (Alavanja and others, 1996). Direct exposure to pesticides by those who handle and work around these materials is believed to pose the greatest risk of human harm, but indirect exposure through trace residues in food and water is also a source of concern (EPA, 1987). The effects of these pesticide residues on infants and children and other vulnerable groups have recently been addressed with a new legislative mandate in the Food Quality Protection Act of 1996 (see box, "Pesticide Tolerance and Dietary Risks" in chapter 3.2, Pesticides). Environmental Quality. Documented environmental impacts of pesticides include: poisonings of commercial honeybees and wild pollinators of fruits and vegetables; destruction of natural enemies of pests in natural and agricultural ecosystems; ground- and surface-water contamination by pesticide residues with destruction of fish and other aquatic organisms, birds, mammals, invertebrates, and microorganisms; as well as population shifts among plants and animals within ecosystems toward more tolerant species. Most insecticides used in agriculture are toxic to honeybees and wild bees, and costs related to pesticide damages include honeybee colony losses, honey and wax losses, loss of potential honey production, honeybee rental fees to substitute for pollination previously performed by wild pollinators, and crop failure because of lack of pollination (Pimentel and others, 1992). Approximately one-third of annual agricultural production in the United States is derived from insect-pollinated plants (Buchman and Nabhan, 1996), and flowering plants in natural ecosystems may not thrive because of fewer pollinators. The destruction of the natural enemies of crop pests has led to outbreak levels of primary and secondary crop pests for some commodities, and pest management costs have increased when additional pesticide applications have been needed for these larger or additional pest populations. Measurable costs related to pesticide residues in surface- and groundwater include residue monitoring and contamination cleanup costs and costs of damage to fish in commercial fisheries. Birdwatching, fishing, hunting and other recreational activities have been affected by aquatic and terrestrial wildlife losses due to pesticide poisonings. An emerging issue is the environmental impacts of invertebrate and microorganism destruction because of the essential role they play in healthy ecosystems. Pesticide Resistance. After repeated exposure to pesticides, insect, weed, and other pest populations in agricultural cropping systems may develop resistance to pesticides through a variety of mechanisms. The newer safety requirements for pesticide registration along with the increasing pace of pest resistance has raised doubts about the ability of chemical companies to keep up with the need for replacement pesticides. In the United States, over 183 insect and arachnid pests are resistant to 1 or more insecticides, and 18 weed species are resistant to herbicides (U.S. Congress, 1995). Cross-resistance to multiple families of pesticides, along with the need for higher doses and new pesticide formulations, is a growing concern among entomologists, weed ecologists, and other pest management specialists. Emerging issues include the impact of endocrine-system disrupting pesticides on human health and wildlife, including potential reproductive effects and effects on child growth and development (EPA, 1997), and the impacts of exposure to pesticides, particularly the potential for synergistic impacts (Arnold and others, 1996). |