A History of Weed Science in the
`United States
`
`SYNGENTA EXHIBIT 1006
`Syngenta v. FMC, PGR2020-00028
`
`

`

`A History of Weed Science
`in the United States
`
`Robert L. Zimdahl
`
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`

`

`Development of herbicides
`after 1945
`
`6 W
`
`e can’t solve problems by using the same kind of thinking we used when we
`created them.
`
`A. Einstein
`
`We live in a society exquisitely dependent on science and technology, in which
`hardly anyone knows anything about science and technology.
`
`Carl Sagan
`
`The chemical era of agriculture developed rapidly after 1945, but it did not
`begin then. In 1000 b.c. the Greek poet Homer wrote of pest-averting sulfur.
`Theophrastus, regarded as the father of modern botany (372?–287? b.c.),
`reported that trees, especially young trees, could be killed by pouring oil,
`presumably olive oil, over their roots. The Greek philosopher Democritus
`(460?–370? b.c.) suggested that forests could be cleared by sprinkling tree roots
`with the juice of hemlock in which lupine flowers had been soaked. In the first
`century b.c., the Roman philosopher Cato advocated the use of amurca, the
`watery residue left after the oil is drained from crushed olives, for weed con-
`trol (Smith and Secoy, 1975).
`Perhaps the first reference to the use of salt to ruin agriculture is from the
`book of Judges (9:45). Abimelech was the first Israelite to become a king,
`but he reigned only 3 years over a small area. He defeated the men of Sechem
`and sowed the city with salt to sterilize the soil (Smith and Secoy, 1976b).
`Historians tell us of the sack of Carthage by the Romans in 146 b.c., who then
`plowed salt into the fields to sterilize them. Later, salt was used as a herbicide
`in England. Several chemicals have been used as herbicides in agriculture for
`a long time, but their use was sporadic, frequently ineffective, and lacked any
`scientific base (Smith and Secoy, 1975, 1976a).
`In 1755, mercurous chloride (HgCl2) was used as a fungicide and seed treat-
`ment. In 1763, nicotine was used for aphid control. As early as 1803, cop-
`per sulfate was used as a foliar spray for diseases. Copper sulfate (blue vitriol)
`was first used for weed control in 1821. In 1855, sulfuric acid was used in
`Germany for selective weed control in cereals and onions. In 1868, Paris
`green (copper acetoarsenite) was used for control of the Colorado potato
`beetle (Leptinotarsa decemlineata). The U.S. Army Corps of Engineers used
`sodium arsenite in 1902 to control waterhyacinth in Louisiana. A California
`research worker, George Gray (1917), published an Agricultural Experiment
`Station Bulletin that reported a dilute solution of sodium arsenite sprayed on
`
`

`

`80
`
`A History of Weed Science in the United States
`
`field bindweed in the Fog Belt of coastal California killed the roots to a depth
`of several feet. The first chemical herbicides can be divided into two groups:
`corrosive fertilizers such as calcium cyanamide and kainit (a mixture of
`magnesium sulfate and potassium chloride); and simple industrial chemicals
`including metallic salts, sulfuric acid, sodium arsenite, ammonium sulfamate,
`and sodium chlorate (Holly, 1986; Norman et al., 1950).
`Bordeaux mixture, a combination of copper sulfate, lime, and water was
`applied to grapevines for the control of downy mildew in the late nineteenth
`century (see Chapter I). Someone in Europe noted that it turned yellow
`charlock (wild mustard) leaves black. That led Bonnet, in France in 1896, to
`show that a solution of copper sulfate would selectively kill yellow charlock
`(now wild mustardBrassica kaber [DC.] L.C. Wheeler) plants growing with
`cereals. In 1911, Rabaté demonstrated that dilute sulfuric acid could be used
`for the same purpose. The discovery that salts of heavy metals might be used
`for selective weed control led, in the early part of the twentieth century, to
`research on heavy metal salts by Frenchmen Bonnett, Martin, and Duclos,
`and German, Schultz (cited in Crafts and Robbins, 1962, p. 173). Nearly con-
`currently, in the United States, Bolley (1908) studied iron sulfate, copper sul-
`fate, copper nitrate, and sodium arsenite for selective control of broadleaved
`weeds in cereal grains. Bolley, a plant pathologist, who worked in North
`Dakota (see Chapter IV), is widely acknowledged as the first in the United
`States to report on use of salts of heavy metals as selective herbicides in cereals.
`The action was caustic or burning with little, if any, translocation. Succeeding
`work in Europe observed the selective herbicidal effects of metallic salt solu-
`tions or acids in cereal crops (Zimdahl, 1995). The important early workers
`were Rabaté (1911, 1934) in France, Morettini (1915) in Italy, and Korsmo
`(1932) in Norway.
`Use of inorganic herbicides for weed management in small grains devel-
`oped rapidly in Europe and England but not in the United States. It is still
`more widespread in Europe than in the United States. Some of the reasons for
`slow development in the United States included lack of adequate equipment
`and frequent failure to obtain weed control because the heavy metal salts were
`dependent on foliar uptake that did not readily occur in the low humidity of
`the primary grain-growing areas of the United States. The heavy metal salts
`worked well only with adequate rainfall and high relative humidity. Other
`agronomic practices such as increased use of fertilizer, improved tillage, and
`new varieties increased crop yield in the United States without weed control.
`U.S. farmers also could always move on to the endless frontier and were not as
`interested, as they would be later, in yield-enhancing technology.
`Carbon bisulfide was first used in agriculture in 1854 as an insecticide in France.
`It was applied as a soil fumigant in Colorado to control Phylloxera, a root-borne
`disease of grapes. In 1906, it was introduced as a soil fumigant for control of
`Canada thistle and field bindweed. It smells like rotten eggs and may have reached
`its peak usage in Idaho in 1936, when over 300,000 gallons were used.
`
`

`

`Development of herbicides after 1945
`
`81
`
`Petroleum oils, introduced for weed control along irrigation ditches and in
`carrots in 1914, are still used in some areas. Field bindweed was controlled
`successfully in France in 1923 with sodium chlorate, which is still used as a
`soil sterilant in combination with organic herbicides. Arsenic trichloride was
`introduced as a product called KMG (kill morning glory) in the 1920s. Sulfuric
`acid, first used in Germany in 1855, was used for weed control in Britain in
`the 1930s. It was and still is a very good herbicide, but is very corrosive to
`equipment and harmful to people.
`Among the first organic herbicides available in the early 1940s was 4,6-dinitro-
`o-cresol (DNOC). It was first synthesized in Russia in the mid-1800s and used
`as a dyestuff, human slimming agent, and an insecticide (Holly, 1986). The first
`successful synthetic organic chemical for selective weed control in cereals was
`2-(1-methylpropyl)-4,6-dinitrophenol or dinitro creysalte (Dinoseb), which
`was introduced in France in 1932 (Dunham, 1973, p. 16; King, 1966, p. 285). It was
`used for many years for selective control of some broadleaved weeds and grasses
`in large-seeded crops such as beans. It is included in the sixth edition of the
`Herbicide Handbook (Anonymous, 1989) but not in the seventh (Ahrens, 1994)
`or eighth (Vencill, 2002), although Dinoterb, a close chemical relative, which
`is not sold in the United States, is in both later editions. Dinoseb is included
`in the Weed Science Society of America (WSSA) list of approved herbicides
`(Anonymous, 2004). Dithiocarbamates were patented as fungicides in 1934. In
`1940, ammonium sulfamate was introduced for control of woody plants.
`In 1940, Pokorny (1941), a chemist, likely employed by the C. B. Dodge
`Company to synthesize new compounds, did what good synthesis chemists do
`when he synthesized 2,4 dichlorophenoxy acetic acid (2,4-D) and 2,4,5-T. Both
`were regarded as chemical curiosities and reported as new compounds in the
`Journal of the American Chemical Society. Neither was reported to have activ-
`ity as a fungicide or insecticide and apparently neither was tested to determine
`herbicidal activity. Other chemists noted the report and decided to investigate
`the possibility of biological activity. Accounts vary about when the first work
`on growth-regulator herbicides was done (Akamine, 1948). Zimmerman and
`Hitchcock (1942) of the Boyce-Thompson Institute (formerly in Yonkers, New
`York and now at Cornell University, Ithaca, New York) first described the
`substituted phenoxy acids (2,4-D is one) as growth regulators (auxin-like
`compounds) but did not report herbicidal activity. They also worked with
`other compounds that eventually became herbicides. They were the first to
`demonstrate that these molecules had physiological activity in cell elongation,
`morphogenesis, root development, and parthenocarpy (King, 1966). A Chicago
`carnation grower’s question, “What is the effect of illuminating gas (acetylene)
`on carnations?” led to the eventual discovery of other plant growth regulating
`substances by Boyce-Thompson scientists (King, 1966). There is much more to
`this fascinating story to be added later in this chapter.
`The effectiveness of monuron, a substituted urea, for control of annual and
`perennial grasses was reported by Bucha and Todd (1951). This was the first of
`
`

`

`82
`
`A History of Weed Science in the United States
`
`many new selective chemical groups with herbicidal activity. The first triazine
`herbicide appeared in 1956 and the first acylanilide in 1953 (Zimdahl, 1995)
`followed by CDAA, the first alphachloroacetamide in 1956 (Hamm, 1974).
`The great era of herbicide development came at a time when world agri-
`culture was involved in the beginnings of the revolutions of labor reduction,
`increased mechanization, and new methods to improve crop quality and
`produce higher yields at reduced cost. Herbicide development built on and con-
`tributed to changing agriculture. Farmers were ready for improved methods of
`selective, chemical weed control. Their acceptance of technological developments
`that changed the practice of agriculture has been characterized in terms of eco-
`nomic, political, social, and philosophical attitudes by Perkins and Holochuck
`(1993). Farmers wanted to improve their operation in competition with other
`farmers and were willing to adopt new technology that enabled them to improve
`their economic competitiveness. New technology was socially acceptable because
`as independent entrepreneurs, farmers could use many technological innovations
`to gain advantage independent of neighbors. Politically, farmers welcomed tech-
`nical assistance that came from public laboratories and land-grant universities
`and government price-support systems that allowed farm operations to remain
`private. Farmers were highly social beings but they remained fiercely independ-
`ent and welcomed opportunities to do what they wanted on their farms. New
`technology developed at no apparent cost to them that could be adopted with-
`out interference from anyone was welcomed. Finally, philosophically, farmers
`perceived that a major part of farming was controlling nature—bending nature
`to human will. Although this was a never-ending challenge, success was appar-
`ent when technology that increased production was readily available. Herbicides
`fit well in each category.
`It is true that no weed control method has ever been abandoned, new ones
`have been added and the relative importance of methods has changed. The
`need for cultivation, hoeing, and so on has not disappeared. These methods
`persist in small-scale agriculture (e.g., I hoe my garden) and in developing
`country agriculture. Older methods have become less important in developed
`world agriculture because of the rising costs of labor, the availability of effec-
`tive chemical controls, and narrower profit margins (Table VI-1).
`A survey of commercially available herbicides in the United States (Kephart,
`1947) documented use of fifty-one different products. Of those, twenty-five
`contained arsenic, five incorporated either nitrophenol or sodium chlorate,
`three were phenoxyacetic acids, a few contained boron or copper salts, and
`others were based on various inorganic materials with herbicidal activity.
`Petroleum-based herbicides, first used in California on non-crop land in 1924,
`were widely used by 1935 in southeastern states. In the early 1940s, petroleum
`oils were used for selective weed control in carrots (Dunham, 1973).
`Rapid development of herbicides occurred after WWII. Shaw (1954) dis-
`cussed the scope of chemical weed control in the United States. He reported
`on six important classes of herbicides (phenoxy and phenoxypropionic acids,
`benzoic acids, substituted phenols, carbamates, substituted ureas, and a few
`
`

`

`Development of herbicides after 1945
`
`83
`
`Table VI-1 The evolution of weed control methods in the United States
`(Alder et al., 1977)
`
`Percent control by year in U.S.
`
`Human energy Animal energy
`(tractor)
`
`Mechanical
`energy
`
`Chemical
`energy
`
`40
`20
` 5
`1
`
`60
`10
`TRa
`TR
`
`70
`40
`24
`
`55
`75
`
`Year
`
`1920
`1947
`1975
`1990
`
`aTR  trace.
`
`Table VI-2 World sales of crop protection products 1960 to 1990 with 2000
`estimated in billions of dollars (Gianessi and Silvers, 2000; Hopkins, 1994)
`
`Pesticide
`
`1960
`
`1970
`
`World pesticide sales
`
`Year
`
`1990
`1980
`(Million U.S. dollars)
`
`1997
`
`2000
`
`160
`Herbicides
`Insecticides 288
`Fungicides
`320
`Other
` 32
`TOTAL
`800
`
` 918
` 945
` 702
` 135
`2,700
`
` 4,756
` 3,944
` 2,204
`
` 696
`11,600
`
`12,600
` 7,840
` 5,600
` 1,960
`28,000
`
`14,700
` 9,100
` 5,400
` 1,700
`30,900
`
`16,560
` 9,360
` 7,560
` 2,520
`36,000
`
`diverse chemical structures) that were in use and in development. By 1954
`most inorganic herbicides were no longer widely used. Shaw said that in 1954
`it was estimated that the then huge amount of 85 million pounds of herbicides
`were used annually in the United States. One of every ten U.S. cropped acres
`was treated with a herbicide. In 2002, 204 selective herbicides were listed in
`the Weed Science Society of America’s Herbicide Handbook (WSSA) (Vencill,
`2002) and 357 had been approved by the Weed Sci. Soc. (Anonymous, 2004).
`In addition there were several experimental herbicides in some stage of
`progress toward marketability. If proprietary labels are considered, there may
`be more than one thousand chemical and biological compounds used for pest
`control in the world (Hopkins, 1994). Table VI-2 illustrates that if dollars of
`product sold are the criterion used, pesticide use has been increasing and her-
`bicide use dominates. In 1997, one billion pounds of pesticides were used in
`the United States and over 47 percent (461 million pounds) were herbicides
`(Gianessi and Silvers, 2000). Just ten herbicides accounted for 75 percent of
`
`

`

`84
`
`A History of Weed Science in the United States
`
`sales (Gianessi and Marcelli, 2000). U.S. farmers routinely apply herbicides to
`more than 85 percent of crop acres (Gianessi and Sankula, 2003). A study of
`forty crops showed treatment of 220 million acres at a cost of $6.6 billion
`(Gianessi and Sankula, 2003). In 2001, the global market for non-agricultural
`pesticides was more than $7 billion per year and was growing about 4 percent
`a year. The global market just for turf pesticides is approximately $850 million
`per year, with about half used on golf courses. Each year U.S. lawn-care firms
`apply about $440 million worth of pesticides.
`The National Agricultural Statistics service of the U.S. Department of
`Agriculture (USDA) regularly surveys selected states and selected crops to
`determine the extent of fertilizer and pesticide use. Reports are available for
`1990 through the current decade at http://usda.mannlib.cornell.edu (accessed
`January 2008; enter herbicides in the search box, click on Agricultural chemi-
`cal usage, and select the category of interest). The data below from 1990, 1996,
`1997, and 2006 show that, with the exception of winter wheat, herbicides
`were used on a major portion of the acreage of each field crop surveyed. The
`specific figures for some of the crops surveyed are shown in Table VI-3. Each
`crop, with the exception of winter wheat, illustrates the dominance of herbi-
`cides for weed control. The soybean data show the dominance of glyphosate-
`resistant (Roundup Ready™) soybeans and the wheat data illustrate the low
`
`Table VI-3 Percent of U.S. crop acres for some major crops treated with herbicides
`over several years
`
`Crop
`
`Percent of acres treated with herbicides in
`
`1990
`
`1996
`
`1997
`
`2006
`
`Corn
`Cotton, upland
`Potato
`Rice
`Soybean
`% of soy bean
`acres treated with
`glyphosate
`Vegetables, 22 crops
`Range
`Average
`Wheat, durum
`Wheat, other spring 89
`Wheat, winter
`
`92
`96
`79
`98
`95
`
`90
`NA
`34
`
`97
`92
`87
`NA
`97
`
`NA
`NA
`NA
`
`96
`97
`83
`NA
`97
`
`92
`
`NA
`93
`NA
`
`NA
`NA
`NA
`95
`98
`
`28–96
`63
`95
`
`49
`
`

`

`Development of herbicides after 1945
`
`85
`
`profitability of the crop and the lack of weed problems for which herbicide
`solutions exist.
`The global herbicide market was estimated to be $13.5 billion from 1990
`to 1993 and a third ($4.5 billion) was the U.S. market. Kiely and colleagues
`(2004) estimated that $14 billion was spent worldwide on chemical weed con-
`trol. Japan was the next largest single country with $1.5 billion in sales. When
`the entire European market is considered, it is second largest, with France
`($1.25 billion) the largest single European country (Hopkins, 1994). In 2001,
`world expenditures on all herbicides was $14,118 million, and 44 percent
`of this in the world and in the United States was herbicides. U.S. users spent
`$6,410 million for 553 million pounds of active ingredient, which was equal
`to 4,987 million pounds of product. These amounts are lower than purchases
`in 2000 and have returned to the levels last seen in the early 1970s (US/EPA,
`2004). Of these amounts, 78 percent is used in agriculture, with the rest nearly
`evenly divided between industrial/commercial/government (12 percent) and
`home and garden use (10 percent).
`In 1990, about 45 percent of world pesticide sales volume was herbicides (sim-
`ilar to the U.S. data), insecticides were 28 percent, and fungicides approximately
`20 percent of total sales volume (Hopkins, 1994). Over 85 percent of herbi-
`cides are used in agriculture. The worldwide market is becoming increasingly
`concentrated in the hands of a few multi-national corporations. Nearly half
`the companies in pesticide discovery (but not in development and marketing)
`in 1994 were Japanese (Hopkins, 1994). The number of companies market-
`ing herbicides in the United States has steadily shrunk from 46 in 1970 to
`7 in 2005 (Appleby, 2005). Three are based in the United States and the others
`are based in Europe, but each operates in the United States (Appleby, 2005,
`personal communication).
`While the number of companies engaged in herbicide discovery, development,
`and sales has steadily declined, the number of available herbicides has stead-
`ily increased. Table VI-4 shows that the number of herbicides listed in the first
`(1967) through the eighth (2002) edition of the Weed Science Society of America’s
`Herbicide Handbook has increased as has the number of different chemical fami-
`lies in which herbicidal activity has been discovered. Similarly, the number of
`
`Table VI-4 The number of herbicides and chemical families in the eight editions of
`the Herbicide Handbook of the Weed Science Society of America
`
`Year of herbicide handbook publication
`
`1967 1970 1974 1979 1983 1989 19941998
`supp.
`
`2002
`
`97
`27
`
`115
` 27
`
`125
` 32
`
`137
` 37
`
`130
` 35
`
`145
` 43
`
`163
` 63
`
`211
` 75
`
`Total herbicides
`Number of
`chemical families
`
`

`

`86
`
`A History of Weed Science in the United States
`
`WSSA-approved herbicides has increased from 304 in 1995 (Anonymous, 1995)
`to 357 in 2004 (Anonymous, 2004). It is clear and not debatable that because of
`their significant production advantages, herbicides dominate modern weed con-
`trol. Timmons (1970) reported 75 herbicides marketed between 1950 and 1969.
`Appleby (2005) included 184 herbicides marketed between 1970 and 2005, an
`increase of 2.4 times. Although the herbicide chemical industry has undergone
`extensive consolidation, as have many other manufacturing industries, it has not
`diminished discovery and development of new herbicides in older chemical fami-
`lies or discovery of activity in new chemical groups.
`Worldwide sales have continued to increase. World exports of pesticides
`of all kinds totaled $15.9 billion in 2004, a new high in sales for the global
`chemical industry (Jordan, 2006). Use of all kinds of pesticides has risen from
`nearly 0.5 kg/ha in 1960 to 2 kg/ha in 2004. The recent increase is attributed
`mainly to the increased use of herbicides on genetically modified crops in
`China (Jordan, 2006).
`A wide range of methods has been offered for vegetation management
`through the use of herbicides. The etymology of herbicide is derived from
`the Latin herba, or plant, and caedere, to kill. Herbicides are chemicals that
`kill plants. The definition accepted by the Weed Science Society of America
`(Vencill, 2002, p. 459) is that a herbicide is “a chemical substance or cultured
`organism used to kill or suppress the growth of plants.” In effect, a herbicide
`disrupts the physiology of a plant over a long enough period to kill it or
`severely reduce its growth.
`Pesticides are chemicals used to control pests. Herbicides differ from other
`pesticides because their sphere of influence extends beyond their ability to
`kill or control plants. Herbicides change the chemical environment of plants,
`which can be more easily manipulated than the climatic, edaphic, or biotic
`environments. Herbicides reduce or eliminate labor and machine requirements
`and modify crop production techniques. When used appropriately they are
`production tools that increase farm efficiency, reduce horsepower, and perhaps
`reduce energy requirements. Herbicides do not eliminate energy requirements
`because they are petroleum-based.
`Understanding the history, nature, properties, effects, and uses of herbicides
`is essential if one is to be conversant with modern weed management. Weed
`management is not accomplished exclusively with herbicides, but they domi-
`nate in the developed world and to most weed scientists they are essential tools.
`Whether one likes them or deplores them, they cannot be ignored. To ignore
`them is to be unaware of the opportunities and problems of modern weed man-
`agement. Ignoring or dismissing herbicides may lead to an inability to solve
`weed problems in many agricultural systems and may delay development of bet-
`ter weed management systems. The majority of weed scientists think carefully
`about the link between what they do and the problems their work will solve
`and the benefits it will provide. They are guided by clear utilitarian goals—to
`provide the greatest good for the greatest number of people. Theirs is a twentieth
`century reason for doing science. It is science driven by the desirable goal of
`
`

`

`Development of herbicides after 1945
`
`87
`
`solving real problems rather than the more traditional goal of intellectual curi-
`osity (see Specter, 2007). In earlier times, “among elite scientists, it was usually
`considered gauche to be obsessed with anything tangible or immediate; brilliant
`discoveries were supposed to percolate” (Specter, 2007). They were rarely inten-
`tional. In the eighteenth and nineteenth centuries, that way of doing scientific
`research was the norm. In agricultural science, most agricultural pest problems
`could not be solved; they could only be studied.
`Although many tried, often with some success, to control weeds in the early
`twentieth century, weed science did not begin until the mid-twentieth century
`when weeds could be controlled by new herbicides, often quite quickly and
`selectively. From the beginning, the purpose of weed science was to solve weed
`problems, primarily those in production agriculture. Weed scientists were in
`the business of reshaping how agriculture was to be practiced. Crafts (1960),
`as he did often and well, told weed scientists in his presidential address to the
`Weed Society of America, what their mission was. Primarily due to monocul-
`tural agriculture, “farmers are at war with weeds, the invaders of his crops.”
`He continued, “at last man has devised tools for combating weeds, commen-
`surate with the tools he uses for mining and manufacture and travel: modern
`mechanical and chemical tools.” These new products contributed to the chemi-
`calization of agriculture and are the “tools of the present day weed researcher.”
`In his speech, Crafts reviewed the early discovery of the inorganic chemicals
`that were used for other purposes, but careful observers noted the death of
`weeds. He pointed out that while the discoveries were apparently accidental,
`“they had to happen.” He saw the development of herbicides as an inevitable
`outcome of progress in plant physiology. In his view, the chemical control of
`weeds did not begin with the discovery of 2,4-D. It was a concept that “had
`to be born” because of accumulated knowledge of plant physiology, plant bio-
`chemistry, and hormone mechanisms.
`Others agreed with Crafts’ idea of the inevitability of progress in weed man-
`agement. For example, the North Central Weed Control Conference was cre-
`ated in 1944 by agronomists and weed scientists who came together with the
`common goal of discovering more effective control, including chemical control,
`of deep-rooted, noxious, perennial weeds, especially field bindweed. It was not
`the post war availability of 2,4-D, but concern about perennial weeds that
`moved scientists and administrators in the fourteen-state North Central region
`to confer. Work on 2,4-D was important, but it was not the reason confer-
`ence was created. The first meeting of the Western Weed Control Conference
`was held in Denver in June 1938 (Appleby, 1993), well before 2,4-D was dis-
`covered. The Conference’s purpose was to foster other regional and a national
`weed control organizations. Progress in weed management had to happen.
`Crafts began a new science focused on weeds at the University of California
`at Davis. He said, “Little did I realize when on July 1, 1931, I initiated weed
`control by scientific methods, that I was starting a technology that, in a mere
`50 years would develop into an industry involving hundreds of effective her-
`bicides that would exceed in cost and magnitude the sum total of all other
`
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`88
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`A History of Weed Science in the United States
`
`pesticides” (Crafts, 1985; Shaw, 1984). Crafts and his mentor and colleague,
`W. W. Robbins, were among the creators of the scientific study of weeds. For
`them it was, because it had to be, a study of weeds rather than their control
`because there was no significant ability to control weeds. They were men born
`in the nineteenth century and educated in the early twentieth century. In 1910,
`feeding the horses and mules necessary to do the work on farms required more
`than one-fourth of the output of the world’s farms and probably a tenth of the
`required work on farms was devoted to caring for the draft animals. In 1922,
`a team of thirty-two mules was required in the state of Washington and much
`of the western United States for wheat harvest. It took one 32-mule team a
`month to harvest 1,200 acres of wheat. In the 1990s, a gas-powered com-
`bine completed the same harvest in a third of the time (Singer, 1998, p. 369).
`Combine harvesters and many other technical and mechanical developments
`were part of what has to be regarded as a revolution in the growing of food.
`It is undeniable that weeds were of concern to farmers and a few scientists.
`There were “three full-time weed men (in the U.S.) in 1934 and not too many
`part-time ones” (Willard, 1951). Oregon appointed the first full-time weed
`specialist in 1936 (Dunham, 1973). By 1951, the USDA had the equivalent of
`seventeen scientists working on weeds. In 1960 there were sixty-six. Buchholz
`(1961) estimated that U.S. states employed only thirty scientists who worked on
`weeds and most of them were part-time. By 1960, Buchholz (1961) estimated
`there were 160 state weed workers, whereas Dunham (1973) estimated, for
`the same time, that there were seventeen states that had twenty full-time weed
`specialists and eighty-nine specialists devoted part-time to weeds. One wonders
`why each of these men (they were all men) began to work on weeds. What
`drew them to weeds? Most were trained as agricultural scientists, but few had
`been involved in educational programs that produced weed scientists—those
`whose education and training focused on weeds. The dilemma of developing
`a discipline that claimed to be an objective science based on the study of a
`subjective class of plants is clear but has not been questioned (Evans, 2002,
`p. 13). Weeds were defined and redefined and while each weed scientist has
`a clear understanding of the objects of study, there is no universal definition,
`shared by all scientists. In 1967 the Weed Science Society of America defined a
`weed as a plant growing where it is not desired (Buchholtz, 1967). In 1989, the
`Society’s definition was changed to define a weed as “any plant that is objec-
`tionable or interferes with the activities or welfare of man” (Humburg, 1989,
`p. 267; Vencill, 2002, p. 462). The European Weed Research Society (1986)
`defined a weed as “any plant or vegetation, excluding fungi, interfering with
`the objectives or requirements of people.” (For other definitions see Zimdahl,
`2007, pp. 17–18). Each definition is clear and each leaves the burden, and
`responsibility for specific identification and final definition, with individuals. It
`is the individual who determines when a particular plant is growing in a place
`where it is not desired or when it interferes with their activities or welfare.
`What was implicit but never made explicit in any definition or