Carl Bell
Emeritus, University of California, San Diego, CA
carl@socalinvasives.com

 

The intentional manipulation of wild plants to become desirable crops was the beginning of agriculture some 10,000 years ago. Along with this beginning came weeds; unwanted plants that prospered in the same human-created environments. Weeds are therefore just as much a part of our domestic culture as the crops. So the history of weed control technology is co-existent with the history of agricultural technology. If you search the internet for the history of agriculture, you will find lots of information. If, however, you search the internet for the history of weeds, you will be disappointed by the lack of literature and references on the subject.

There are some likely explanations for this lack of information. One is that, according to Wikipedia, crop production was generally sufficient through the succeeding millennia to meet normal human needs. So even though weeds were present, the available control methods were apparently adequate. The earliest known weed control technology in 8000 BCE was the plow and hand-weeding (which includes hand-pulling, cutting with a knife, hoes and mattocks). It stayed that way for the next 10,000 years until the 18^th Century CE; so there was not much to write about. And why was that? It was because there was an abundance of labor, mostly women and children, to hand-weed^[1]. It is not surprising, therefore, that the beginning of the industrial age in Europe was accompanied by improvements in weed control technology; not just because it was an age of invention but also because women and children were being pulled off farms to work in industry. Women and children have apparently always gotten the short end of the stick, but the idea that the only way to get them out of the fields is to put them in factories should make us ashamed.

The idea that the plow and hand-weeding was the sum total of weed control technology for 10 millennia is biased by the western prejudice that the middle-east was the sole origin of agriculture; ignoring the seven or so other places in the world where plants and animals were domesticated independent of the Levant. But more on that later, let's start with the plow and hoe. It seems obvious that some kind of hand tool was the first crop production technology, used to break up the soil before planting and also chop weeds as the season progressed. But later with the domestication of oxen, horses and camels, animal traction was teamed up with larger plows. The earliest plows were made of wood. With the development of iron making in 1,000 BCE or so, plows were fitted with iron plowshares that improved their ability to work hard or rocky soils. Additionally iron hoes date back to Greek and Roman days.

The name that stands out in the industrial age with regard to weeds is Jethro Tull (1674-1741), a gentleman farmer in England. He invented the grain drill and cultivation tools. Actually, Romans and farmers in India were using similar tools 2,000 years ago, but they were never in widespread use (likely because of the abundance of women and children for labor); so maybe we should say that Tull re-invented these tools. Regardless, Tull's grain drill and cultivation ideas were widely adopted and replicated in the 18^th Century, aided by the ease of creating and distributing printed materials like newspapers, books and pamphlets. Tull's creations fostered the rapid development of these types of tools in Europe and North America, and formed the basis of what was called the British Agricultural Revolution. The grain drill did a simple thing; it planted the grain crops in rows. Before the drill, crops were hand-scattered over plowed fields. The weeders, the women and children, had to take time to make sure they were weeding just the weeds and not the crop; so having all of the crop seed in rows meant that anything outside the crop row was a weed; much simpler. It also allowed Tull's cultivation tool, a horse-drawn harrow to be used between the crop rows to loosen the soil between the drill rows and to kill weeds.

Cultivation tools have been the mainstay of weed control for the past three centuries. These tools, using animal traction and later tractors, became quite varied and specialized. The drawing on the right (borrowed from the new California Weed Science Society book discussed below) shows just a few of the knives, sweeps, spikes and harrows that have been created for weeding crops. One of the most useful and inventive tools in California was the sled planter system. This tractor-drawn implement was a platform with runners that ran in the furrows. The sled hugged the beds and kept the platform closely in line with the bed-top. During a cropping season, the sled was first outfitted with planters, which sowed seed in very straight lines. After the crop germinated, cultivation tools were fitted on the sled just off the seed lines. This tool allowed cultivation very close to the emerging crop, usually within two inches on both sides of the seedline. Some of the other ingenious cultivation tools, many developed on farms in California for specific purposes, include flexible tine and rod weeders; rotary hoes; and finger weeders. In orchard crops, cultivation implements like the French Plow cultivate weeds in the vine row, but then through a mechanism, are automatically pulled back away from the vine or tree trunk. These tools are discussed thoroughly in the fourth edition of Principles of Weed Control (available as an ebook or printed through Amazon and Barnes and Noble). The success of cultivation for weed control has been remarkable, but close guidance to crops, especially between crops in the seedline has always been the major challenge. The realization of robotic weeders in recent years has been very exciting. Robotic systems and digital guidance only happened, in my opinion, because there was a highly developed practice of mechanical cultivation to build upon and because California farmers are innovators and early adopters of new technologies.

In other parts of the world, where agriculture developed independent of the Mideast, weed control took some interesting forms. In the east, rice was domesticated about the same time as cereal grains in the Mideast. But because it is grown in water, crop production practices were different but weeds were still a problem. By at least 3,000 BCE grass carp were a part of rice production in flooded paddies. This might have been serendipity, some fish got into the paddy because of a monsoon rain or a break in the dikes and the farmers noticed that they ate weeds, and also some insect pests. So putting fish, mostly grass carp but also tilapia and other species, into rice paddies is a common practice from Japan to India. The fish is also an agricultural commodity, so it's a win-win situation.

In the US rice is typically direct seeded like other grain crops, but in Asia it is sown as transplanted seedlings. Transplants minimize weed and some other pest problems because the rice plants have a head start over the pests. In one sense, this reduced weeding labor requirements, but this is balanced against greater labor need for the transplanting. This practice also goes back millennia. So farmers from Asia initiated agricultural practices that conform to the Integrated Pest Management (IPM) philosophy long before it came to be a part of our language in the west. And it may be that farmers in Asia have a different view of weeds than we do. Clyde Elmore, Emeritus UC Weed Scientist and a long time contributor to the California Weed Science Society, related an incident from an agricultural tour of China. On the tour he asked one of the hosts about the abundance of weeds on rice levees and roadsides, wanting to know how these weeds were controlled. The reply was. “What weeds, those plants are fodder for our pigs.” I saw sheep grazing on rice levees in Australia and was told it was a common practice, the only problem being when a sheep slipped off the levee into the paddy. Sheep are raised mostly for wool ‘downunder' and a wet sheep is pretty heavy.

In the New World there were no draft animals, so plowing never developed. Instead a common farming method was ‘slash and burn' (also known as ‘fire and stick'), where an area of forest or brush is burned, then roughly cleared for planting. Crops are sown by making a small opening into the soil with a stick and dropping in seed. In what is called the Milpa system in Mexico and the three sisters in the US three crops were sown together. These were corn (maize), squash and bean. The squash germinated and grew quickly, creating a cover crop for the corn and bean. The corn grew tall, providing a pole for the beans. This integrated system delivered carbohydrates from the corn, protein from the bean and anthocyanins plus fiber from the squash; simple and nutritious. When the notion of cover crops was being introduced in the US in the 1980's, the Milpa was often referenced as the model.

For most agronomists and weed scientists in the 20^th century, the history of technology in weed control is the history of herbicides. For some it didn't begin until the introduction of synthetic herbicides in about 1950. In reality, herbicides, in the sense of chemicals used intentionally on a crop for weed control started in the mid 19^th Century. The first herbicides were inorganic salts such as sodium chloride, sodium chlorate, arsenic salts and carbon bisulfide as a fumigant. In addition various oils, inorganic acids like sulfuric acid, and solvents were used as burn-down herbicides. All of these chemicals were used at what today would be unbelievable rates, 600-1000 pounds per acre for sodium chlorate for example. They were toxic and some were extreme fire hazards. This same period also saw advances in weed biology and ecology, which included research into weed seed in the soil, the role of below ground asexual reproduction, plant competition, weed seed movement in animal feces, and other fundamental studies. Much of this foundational biological information is still the best work in the literature today.

The discovery of 2,4-D and the chemical synthesis process that allowed for this discovery opened the floodgates for herbicides. By 1969, a scant two decades later, there were 75 modern organic molecule herbicides on the market for use on farms, in industrial settings, in landscapes and elsewhere. According to a genealogy created by Arnold Appleby, Emeritus Professor of Crop Science at Oregon State University, there have been about 80 herbicide discovery companies in the US since the 1950's. Today there are about 10 active companies in the US due to consolidation and acquisition. The ninth edition of the Herbicide Handbook published by the Weed Science Society of America in 2007 includes more than 200 herbicides presently in use or in development in the US. It is useful to reflect that in 2007 herbicides represented 44% of the total pesticide use in the US and 39% of the world market, while insecticides are 9% and 18% respectively. In developing nations, herbicides are less commonly used. In India, for example, herbicides are only 16% of the pesticide market and in Pakistan only about 5%.

It has been known for a long time that the use of weed control technologies is inversely correlated with poverty and the abundance of women and children for weeding. So technology is not something that is uniformly available. It may be hard to imagine that the latest technology, the robotic weed control machines, will ever be developed for small scale use, like on a family farm in Pakistan, but it is perhaps better to ask, “Why not?”

 

^[1] See http://croplifefoundation.files.wordpress.com/2012/05/solving-africas-weed-problem-report1.pdf for an excellent discussion of this issue as it exists today in Africa. This Crop Life Report states that smallholder farms spend 50-70% of their labor handweeding; that women contribute 90% of the handweeding labor; and 69% of farm children aged 5-14 miss school during peak weeding periods.