alternative measures of pesticide use

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Alternative Measures ofPesticide UseC. Barnard PhD a & N. D. Uri PhD ba Economic Research Service, U.S. Department ofAgriculture , Washington, DC, 20005, USAb Natural Resources Conservation Service, U.S.Department of Agriculture , Beltsville, MD, 20705,USAPublished online: 21 Oct 2008.

To cite this article: C. Barnard PhD & N. D. Uri PhD (1999) Alternative Measures ofPesticide Use, Journal of Health & Social Policy, 11:2, 31-40

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Alternative Measures of Pesticide Use

C. Barnard, PhDN. D. Uri, PhD

ABSTRACT.While kilograms of pesticide is the most common way ofmeasuring agricultural chemical use, the type of analysis will generallydefine what measure of chemical use is best. In this paper differentmeasures are considered. The inferences one draws concerning pesti-cide use can vary substantially depending on the measure. [Article copiesavailable for a fee from The Haworth Document Delivery Service:1-800-342-9678. E-mail address: [email protected]]

KEYWORDS. Pesticide, alternative measures, agriculture, chemical use

INTRODUCTION

While kilograms of pesticide material used is the most common method ofmeasuring agricultural chemical use in the United States, the type of analysisundertaken will define what measure of chemical use is most appropriate. Forexample, quantifying the risk from the exposure to pesticides typically re-quires weighing usage or residues by acute or chronic health and environ-mental toxicity coefficients and subsequently estimating human or environ-mental exposure to such hazards. The inferences associated with alternativemeasures of pesticide use is the subject of what follows.

C. Barnard is Senior Economist for the Resource Economics Division, EconomicResearch Service, U.S. Department of Agriculture, Washington, DC 20005. N. D.Uri is Program Analyst for the Resource Inventory Division, Natural ResourcesConservation Service, U.S. Department of Agriculture, Beltsville, MD 20705.

The views expressed are those of the authors and do not necessarily represent thepolicies of the U.S. Department of Agriculture or the views of other U.S. Departmentof Agriculture staff members.

Journal of Health & Social Policy, Vol. 11(2) 1999E 1999 by The Haworth Press, Inc. All rights reserved. 31

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JOURNAL OF HEALTH & SOCIAL POLICY32

PESTICIDE USE IN THE UNITED STATESAS COMMONLY MEASURED

Pesticide use in agriculture in the United States increased until the early1980s, coinciding with the growth in crop acres and a larger share of cropacres receiving pesticide treatments. Since the 1982 peak in crop acresplanted, the quantity of pesticide active ingredients used by farmers hasfluctuated between 0.44 and 0.47 million metric tons. The annual fluctuationshave partially been in response to changes in crop acres, government set-aside requirements, and pest infestations, but also reflect some trends in theintensity of use per acre and the effect of newer products applied at lowerrates than the older products they replaced.Pesticide products are classified as herbicides, insecticides, fungicides,

and ‘‘other’’ pesticides. Table 1 shows details about the type and quantity ofpesticides applied to major field crops, fruits and vegetables. The major cropproducing areas of the United States, not surprisingly, dominate the distribu-tion of the application rate. The heaviest application rates occur in the potatogrowing region of Idaho and the apple producing regions of Washington andOregon.While the conventional measurement units of pesticide use provide a

relative indication of intensity of use, they fail to account for differences inproduct characteristics or changes in the mix of products over time. Becauseeach pesticide ingredient can differ greatly in its toxicity, persistence, andmobility, other measurement units are needed to reflect any changes in thehealth or environmental risks posed by pesticides. Introduced in the nextsection are constructed measures which adjust for different toxicity and per-sistence characteristics and illustrate how these characteristics have changedover time. Due to pesticides whose registrations were canceled (i.e., thechemical can no longer be used such as DDT, aldrin, and chlordane), changesin use restriction, and shifts to less toxic chemicals, the perception that healthand environmental risks parallel the aggregate changes in pesticide quantitiesis not necessarily valid.

ALTERNATIVE MEASUREMENT OF PESTICIDE USE

Pesticide use in the United States, as traditionally reported, reached recordlevels in 1994. But, for assessing the human-health and environmental im-plications of pesticide use, weight of the materials may not be the most usefulindicator of pesticide use. The amount of pesticides applied, measured inkilograms or acres treated, fails to account for the wide variation both intoxicity per kilogram and persistence in the environment which characterizes

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C. Barnard and N. D. Uri 33

TABLE 1. Estimated Quantities of Pesticide Active Ingredients Applied toSelected U.S. Crops, 1964-951

Commodities 1964 1966 1971 1976 1982 1990 1991 1992 1993 1994 1995

1,000 metric tons of herbicidesCorn 13.1 23.7 52.1 106.7 125.5 112.1 108.3115.63104.1 111.1 96.4Cotton 23.8 3.4 10.1 9.4 10.78 10.9 13.4 13.3 12.1 14.7 19.9Wheat 4.7 4.3 6.0 11.3 10.1 8.6 7.0 8.9 9.4 10.7 10.3Sorghum 1.0 2.1 5.9 8.1 8.1 6.9 7.3 na na na naRice 1.3 1.5 4.1 4.4 7.3 8.3 8.3 9.1 na na naSoybeans 2.2 5.4 18.8 41.8 68.7 38.4 36.0 34.7 33.0 35.7 35.1Peanuts 1.5 1.5 2.3 1.7 2.5 2.1 2.3 na na na naPotatoes 0.7 1.1 1.1 0.9 0.8 1.2 1.3 1.1 1.3 1.5 1.5Other Vegetable1.1 1.8 1.7 2.8 2.2 2.5 2.4 3.0 3.0 3.1 3.2Citrus 0.1 0.2 0.3 2.5 3.2 2.9 3.1 2.9 2.6 2.5 2.4Apples 0.1 0.2 0.1 0.3 0.3 0.2 0.2 0.2 0.2 0.3 0.4Other Fruit 0.4 0.9 0.3 0.3 0.3 0.9 0.9 0.9 0.9 1.0 1.0

1,000 metric tons of insecticidesCorn 8.1 12.2 13.2 16.5 15.5 11.9 11.9 10.8 9.5 8.9 7.7Cotton 40.2 33.5 37.8 33.1 9.9 7.0 4.2 7.9 7.9 12.3 15.5Wheat 0.5 0.5 0.9 3.7 1.5 0.5 0.1 0.6 0.1 1.0 0.5Sorghum 0.4 0.4 2.9 2.4 1.3 0.6 0.6 na na na naRice 0.1 0.2 0.5 0.3 0.3 0.1 0.2 0.1 na na naSoybeans 2.6 1.7 2.9 4.1 6.0 4.1 0.2 0.2 0.1 0.3 0.3Peanuts 2.8 2.9 3.1 1.3 0.5 0.9 1.0 na na na naPotatoes 0.8 1.5 1.4 1.7 1.9 1.9 1.9 1.8 2.0 2.3 1.6Other Vegetable4.3 4.2 4.3 2.9 2.3 2.4 2.3 2.8 2.7 2.9 2.9Citrus 0.7 1.5 1.6 2.4 2.7 1.4 2.1 2.3 2.7 2.6 2.7Apples 5.6 4.4 2.5 1.9 1.7 1.9 2.1 2.0 2.1 2.0 1.8Other Fruit 0.9 2.1 1.3 1.7 1.0 2.5 2.5 2.5 2.6 2.8 2.9

1,000 metric tons of fungicidesCorn 0 0 0 10.3 35.6 0 0 0 0 0 9.8Cotton 0.1 0.2 0.1 0.1 0.1 0.5 0.4 0.4 0.4 0.5 0.5Wheat 0 0 0 0.4 0.6 0.1 0.1 0.6 0.4 0.5 0.3Sorghum 0 0 0 0 0 0 0 na na na naRice 0 0 0 0 0.1 0.1 0.2 0.2 na na naSoybeans 0 0 0 0.1 0.1 0 0 0.1 0 0.1 0.1Peanuts 0.6 0.6 2.3 3.5 2.4 3.8 4.2 3.5 na na naPotatoes 1.7 1.8 2.1 2.1 2.1 1.4 1.6 1.9 2.3 3.3 4.1Other Vegetable2.3 2.1 2.9 2.6 3.4 6.7 6.8 8.9 9.6 11.3 11.2Citrus 2.5 2.1 4.8 3.0 2.5 1.3 1.9 1.8 1.7 1.8 2.1Apples 4.0 4.4 3.7 3.3 2.9 2.2 2.3 2.3 2.4 2.4 2.4Other Fruit 0.8 1.4 1.5 2.0 1.3 2.1 2.2 2.2 2.2 2.3 2.3

1,000 metric tons of other pesticidesCorn 0.1 0.3 0.2 0.3 0.1 0 0 0 0 0 0Cotton 6.4 7.3 9.6 6.5 4.8 7.8 8.0 8.1 6.5 8.0 10.1Wheat 0 0.1 0.2 0 0 0 0 0 0 0 0Sorghum 0 0.1 0 0.2 0.1 0 0 na na na naRice 0 0 0 0 0.1 0 0 0.1 na na naSoybeans 0 0.1 0.1 1.00 1.3 0 0 0 0 0 0

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TABLE 1 (continued)

Commodities 1964 1966 1971 1976 1982 1990 1991 1992 1993 1994 19951,000 metric tons of other pesticides

Peanuts 3.6 3.6 0.2 0.6 0.8 1.2 1.4 na na na naPotatoes 0.1 0 3.3 4.4 7.8 18.1 23.5 25.6 41.1 40.3 37.6Other Vegetable2.9 0.3 1.8 2.6 3.2 8.9 9.3 12.5 14.2 17.2 17.2Citrus 0.8 0.4 0.7 0.1 0 0 0 0 0.1 0.1 0.1Apples 0.5 0.6 0.3 0.3 0.2 0.1 0.1 0.1 0.1 0.1 0.1Other Fruit 0.2 0.8 0.3 0.3 0.1 0.1 0.1 0.1 0.3 0.6 na

1,000 metric tons of all pesticide typesCorn 21.2 36.2 65.5 123.5 141.1 124.1 120.2 126.4113.6 120.1 103.8Cotton 49.1 44.3 57.7 49.1 25.5 26.2 25.9 29.7 26.9 35.6 43.1Wheat 5.2 4.7 7.0 15.4 12.1 9.2 7.1 10.1 9.9 12.2 11.1Sorghum 1.4 2.5 8.9 10.6 9.4 7.5 7.9 na na na naRice 1.5 1.6 4.6 4.6 7.6 8.5 8.7 9.4 na na naSoybeans 4.7 7.0 21.7 46.9 75.9 38.4 36.3 34.9 33.2 35.8 35.4Peanuts 8.5 8.5 7.9 7.1 6.3 7.9 8.8 na na na naPotatoes 3.1 4.5 8.0 9.2 12.7 22.6 28.3 30.4 35.2 48.2 44.8Other Vegetable10.7 8.4 10.7 10.9 11.2 20.5 20.8 27.2 29.5 34.5 34.4Citrus 4.2 4.1 7.3 8.0 8.5 5.7 7.0 6.9 7.1 7.0 7.2Apples 10.3 9.5 6.6 5.8 5.2 4.3 4.7 4.5 4.8 4.7 4.7Other Fruit 2.2 5.2 3.4 3.8 2.9 5.6 5.7 5.7 5.7 6.4 6.8

1Estimates are constructed for the total U.S. acreage of the selected commodities. In yearswhen the surveys did not include all states producing the crop, the estimates assume similar userates for those states.Source: USDA, ERS, AER-717 (prior to 1993) and unpublished USDA survey data following1993.

the continuously changing array of more than 350 active ingredients thathave been used in U.S. agricultural production in the last 40 years. Alterna-tive measures of pesticide use, recently developed to measure pesticide use interms of toxicity- and persistence-adjusted units, indicate a dramatically dif-ferent trend in use over the 1964 to 1992 period.Pesticide weight, as a measure of pesticide use, has two particularly nota-

ble drawbacks when used for evaluating the potential for harm to humanhealth and the environment. First, pesticide active ingredients vary widely interms of toxicity per unit of weight, irrespective of the scale used to measuretoxicity.1 Second, weight does not account for the persistence of the pesticidein the environment. The longer a pesticide ingredient remains active in theenvironment, the more potential there is for it to come in contact with unin-tended species. Persistence varies widely between active ingredients, butmany modern pesticides have half-lives (the typical measure of persistence)in the range of 10 to 100 days.A general perception is that, over time, there has been significant reduc-

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tion in overall toxicity (especially in terms of measures relevant to long-termhuman health) of the substances applied in the environment as agriculturalpesticides (Carlson and Wetzstein [1993] and Zalom and Fry [1992]). Thisperception is apparently based partly on the observation that many newpesticide compounds are applied at lower rates (kilograms per acre) and areless persistent in the environment. In addition and as noted previously, anarray of formerly widely-used, but relatively highly toxic and persistentingredients have been banned by the EPA. The information in this sectionprovides a quantitative assessment of the accuracy of these perceptions.Adjustment factors are used to convert historical pesticide-use data (collectedand reported in terms of kilograms of active ingredients applied) into Persis-tence Units, Toxicity Units and Toxicity-Persistence Units. These terms aredefined below and are more meaningful than kilograms applied with respectto potential environmental and human health impacts. The weighing schemeadopted creates common denominators that reflect variation in toxicity andpersistence among individual pesticide ingredients. Thus, the amounts ofeach pesticide active ingredient applied are aggregated via common units thatare consistent across time, regions, pesticide types, toxicity, and persistence.This approach is consistent with other indexes designed to make assessmentsof aggregate changes in pesticide toxicity and persistence (e.g., Kovack et al.[1992] and Levitan et al. [1995]). The measures are converted to indexes toavoid the difficulties associated with measures that are not unit free. This isuseful when the concern is with trends or the changes in toxicity and persis-tence relative to some base period. In these instances, the precise units associ-ated with the measurement of persistence or toxicity are unimportant.Persistence units (PERSIST) are based on soil half-life. This is length of

time it takes for a pesticide to break down to half of its initial concentration.The soil half-life is highly dependent upon environmental conditions such assoil pH and climate. Organochlorines and some organophosphates tend to bevery persistent in the environment. PERSIST units are created by calculatingthe half-life of one kilogram of each pesticide active ingredient. Multiplica-tion of the index number for each pesticide active ingredient by kilogramsapplied yields the total PERSIST units for each pesticide ingredient. ThePERSIST units for each ingredient are then summed to obtain an aggregatemeasure of PERSIST. That is,

(1) PERSISTt = (Σi (�i ρit)/Σi (�iρi(base)))

where PERSIST denotes the pesticide persistence index, �i denotes the half-life of one kilogram of pesticide i, ρit denotes the number of kilograms ofactive ingredient of pesticide i applied in period t, and ρi(base) denotes thenumber of kilograms of active ingredient of pesticide i applied in the baseperiod. The summation is across all pesticides i.

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Toxicity units (TUs) are based on indexes of the toxicity of each individualactive ingredient. TUs are created by calculating the number of units (refer-ence dose or LD50--see below) contained in one kilogram of each pesticideactive ingredient. Multiplication of the index number for each pesticide ac-tive ingredient by kilograms applied yields the total TUs for each pesticideingredient. The TUs for each ingredient are then summed to obtain an aggre-gate measure of TUs. That is,

(2) CHRONIC-TUs = (Σi(�iρit)/Σi(�iρi(base)))

where CHRONIC-TUs denotes the pesticide chronic toxicity units index, �idenotes the reference dose of one kilogram of pesticide i, ρit denotes thenumber of kilograms of active ingredient of pesticide i applied in period t,and ρi(base) denotes the number of kilograms of active ingredient of pesticidei applied in the base period. The summation is across all pesticides i. Foracute toxicity,

(3) ACUTE-TUs = (Σi (�iρit)/Σi(�iρi(base)))

where ACUTE-TUs denotes the pesticide acute toxicity units index, �i de-notes the reference dose of one kilogram of pesticide i, ρit denotes the num-ber of kilograms of active ingredient of pesticide i applied in period t, andρi(base) denotes the number of kilograms of active ingredient of pesticide iapplied in the base period. The summation is across all pesticides i.Toxicity-Persistence Units (TPUs) are based on further adjustment of the

TUs to account for the combined toxicity and persistence of each individualactive ingredient. The TPU index numbers are created by multiplying thetoxicity index numbers (number of units of reference dose or LD50 containedin one kilogram of active ingredient) by the number of days (as measured byhalf-life) that an application of the active ingredient remains active in theenvironment. These Toxicity-Persistence index numbers are multiplied bythe kilograms of their respective active ingredient used and then summed toget aggregate TPUs. That is,

(4) CHRONIC-TPUs = (Σi(�ibiρit)/Σi (�ibiρi(base)))

where CHRONIC-TPUs denotes the pesticide chronic toxicity-persistenceunits index and the other terms are as previously defined. Acute toxicity-per-sistence units are defined as

(5) ACUTE-TPUs = (Σi(�i�iρit)/Σi(�i�iρi(base)))

where ACUTE-TPUs denotes the pesticide acute toxicity-persistence unitsindex and the other terms are as previously defined.

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Five separate measures of pesticide use are created for comparison tokilograms of active ingredients. The first measures the persistence of pesti-cides in the environment. The next two measures (labeled Toxicity Units orTUs) adjust kilograms applied for two alternative measures of pesticide tox-icity. One of these measures adjusts kilograms applied for chronic toxicityusing an indicator of long-term human health called the reference dose.2

These units are labeled CHRONIC-TUs. The other measure adjusts kilo-grams applied for acute pesticide toxicity using an indicator of acute mam-malian toxicity called Oral LD50.3 These units are labeled ACUTE-TUs. Theacute measure is more relevant to one-time exposures while the chronicmeasure is relevant to daily exposure over an extended period.The two toxicity measures can be further adjusted to account for persis-

tence of individual pesticides in the environment. This adjustment, based onpesticide half-life, creates two additional measures called Toxicity-Persis-tence Units (TPUs). The terms CHRONIC-TPUs and ACUTE-TPUs are usedto distinguish the TPU measures based on the reference dose from the onebased on Oral LD50.Aggregate pesticide use is compared in Table 2 for four points in time:

1964, 1966, 1971, and circa 1992. Comprehensive pesticide use data allow-ing for the computation of TUs and TPUs are available only for these years.Pesticide use is compared first on the basis of kilograms of active ingredientapplied, then on the basis of the two variations in the TUs and TPUs mea-sures.The TU and TPU indexes are simple measures related to the potential for

exposure to chemicals with health effects. They do not reflect actual expo-sures. For example, these indicators do not consider how product formulation(e.g., liquid and granular forms and/or carrying agents) or application equip-ment have changed nor do they consider the proximity of humans who couldbe exposed. Such considerations would affect exposure and risk measuresassociated with chemical applications.Table 2 shows that aggregate pesticide use in 1992 was 264 percent of the

use in 1964, when measured by kilograms of active ingredient. When mea-sured by PERSIST, which adjusts for the half-life of the pesticides applied,the 1992 index is 55 percent greater than the 1964 value. When measured byCHRONIC-TUs, which adjusts for just toxicity based on the reference dose,the 1992 indicator is 30 percent below the 1964 level. Finally, when mea-sured by CHRONIC-TPU, which adjusts for persistence and toxicity, the1992 use is 89 percent below the 1964 use level. Clearly, the different seriesportray a dramatically different picture both of current use among pesticidetypes and of the change in pesticide use over time, with correspondinglydifferent implications for human health and the environment. When pesticideuse is measured in units that adjust for persistence and chronic human toxic-

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TABLE 2. Index (1964 = 100) of relative use of pesticide active ingredients forselected years, comparing kilograms and persistence, chronic toxicity, acutetoxicity, and chronic and acute toxicity/persistence units.1/

Pesticide type Units 1964 1966 1971 1992

Herbicides:kilograms 100 160 364 717PERSIST 100 198 493 1381

CHRONIC-TUs 100 141 338 684ACUTE-TUs 100 136 246 321

CHRONIC-TPUs 100 163 344 838ACUTE-TPUs 100 145 283 705

Insecticides:kilograms 100 95 107 57PERSIST 100 94 68 18



Fungicides:kilograms 100 98 139 159PERSIST 100 116 112 348



Other Pesticides:kilograms 100 85 112 404PERSIST 100 61 181 105



Total Pesticides:kilograms 100 109 171 264PERSIST 100 99 120 155



1/ Estimates are constructed for corn, soybeans, wheat, cotton, sorghum, rice, peanuts, potatoes,other vegatables, citrusSource: USDA, Economic Research Service Estimates

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ity, it is clear that the character of current pesticide use is significantly differ-ent than it was in 1964, 1966 and 1971. Much of the reduction in PERSIST,CHRONIC-TUs and CHRONIC-TPUs since 1971 corresponds to the remov-al from the pesticide market of many organochlorine pesticides, such asaldrin, DDT, chlordane, and toxaphene.Indicators of PERSIST, CHRONIC-TUs and CHRONIC-TPUs for herbi-

cides and fungicides have increased substantially since 1964, while those forinsecticides have declined in equally dramatic fashion. Insecticides accountfor such a large share of CHRONIC-TUs and CHRONIC-TPUs, however,that the increased volume of herbicides and fungicides did not offset thedecline in insecticide PERSIST, CHRONIC-TUs and CHRONIC-TPUs. In-secticides account for more that 50 percent of the total CHRONIC-TUs andCHRONIC-TPUs and 75 percent of PERSIST currently. In 1964, insecticidesaccounted for 75 percent of total PERSIST, 80 percent of all CHRONIC-TUsand 97 percent of all CHRONIC-TPUs.The picture is quite different when toxicity is defined in acute terms. Table

2 indicates that the ACUTE-TU indicator for pesticides is 55 percent greaterthan it was in 1964 and when measured by ACUTE-TPUs is 10 percentgreater in 1992. The implication is that the amount of ACUTE-TUs andACUTE-TPUs applied in the environment by use of the current array ofpesticides is greater than in 1964. Herbicide and fungicide ACUTE-TPUshave increased dramatically (though neither accounts for a major percentageof total ACUTE-TPUs), while the insecticide measure has remained at rough-ly the same level. The aggregate insecticide ACUTE-TPUs is similar to 1964levels, and has continued to account for slightly more than 91 percent of totalACUTE-TPUs. The insecticide ACUTE-TUs is currently above the 1964level by more than 50 percent while it continues to account for approximately94 percent of total ACUTE-TUs.

CONCLUSION

The fact that one kilogram of a pesticide is not necessarily equal to akilogram of a different pesticide can be significant depending on how pesti-cide information is used. While kilograms of pesticide material used is themost common method of measuring agricultural chemical use, the type ofanalysis undertaken will define what measure of chemical use is appropriate.Quantifying the risk from the exposure to pesticides, for example, typicallyrequires weighing usage or residues by acute or chronic health and environ-mental toxicity coefficients and subsequently estimating human or environ-mental exposure to such hazards. The inferences one draws concerning pesti-cide use can vary substantially depending on the measure considered.

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NOTES

1. Numerous measures of toxicity exist for individual pesticide active ingredients,including those designed to measure chronic and acute toxicity to humans, and toxi-cities to various avian, aquatic, and beneficial insect species. The relative toxicity ofeach pesticide ingredient varies depending upon which measure is used, and for agiven measure, there is wide variation in toxicity among pesticide ingredients.

2. The reference dose represents the maximum daily human exposure to that pes-ticide that results in no appreciable risk. The reference dose for each pesticide is de-termined from the no-observed-effect-level (NOEL) multiplied by a safety factorwhere NOEL is the maximum dose level (amount of pesticide/amount of bodyweight/day) at which no effects attributable to the pesticide under examination can befound.

3. LD50 is used to measure the oral and dermal toxicity of a chemical and is ex-pressed in terms of weight of the chemical per unit of body weight (e.g., mg/kg). Itmeasures the amount of the toxicant necessary to kill 50 percent of the organismsbeing tested within a specified time period. The U.S. Environmental ProtectionAgency has identified the most toxic pesticides as being in Toxicity Class I and in-cludes such pesticides as 2,4-D, methyl bromide, metam sodium, dicamba, terbufos,parathion, methomyl, and carbofuran.

REFERENCES

Calson, G., and M. Wetzstein, ‘‘Pesticides and Pest Management,’’ in Agriculturaland Environmental Resource Economics, G. Carlson, D. Zilberman, and J. Mira-nowski, eds., Oxford University Press, New York, 1993.

Kovach, J., C. Petzold, J. Degni, and J. Tette, ‘‘A Method to Measure the Environ-mental Impact of Pesticides,’’ New York’s Food and Life Sciences Bulletin, Vol.139 (1992), pp. 33-47.

Levitan, L., I. Merwin, and J. Kovach, ‘‘Assessing the Relative Environmental Im-pacts of Agricultural Pesticides: The Quest for a Holistic Method,’’ Agriculture,Ecosystems, and Environment, Vol. 55 (1995), pp. 153-168.

McIntosh, C.S. and A.A. Williams, ‘‘Multiproduct Production Choices and PesticideRegulation in Georgia,’’ Southern Journal of Agricultural Economics, Vol. 24(1992), pp. 135-44.

U.S. Department of Agriculture, Crop Production, AER-717, Economic ResearchService, Washington, 1993 and earlier.

Zalom, F., and W. Fry, Food, Crop Pests, and the Environment, APS Press, St. Paul,MN, 1992.

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alternative measures of pesticide use

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