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WEEDS. Etymologically, "weed" derives from the Old English word for "grass" or "herb," but during the Middle Ages the meaning has changed to indicate an undesirable plant that grows where it is not wanted, especially among agricultural plots. This has historically been the primary meaning of the word, although in the nineteenth century, American writers grew increasingly aware that calling a plant a "weed" was an arbitrary human judgment, as there is no natural category of weeds. In the words of Ralph Waldo Emerson, a weed "is a plant whose virtues have not yet been discovered." Today, biologists tend to share that opinion, since many of the plants that are designated as weeds are, in fact, closely related to popular crops. Indeed, "weed" has fallen out of usage among biologists, although those who study agriculture still find the term useful in discussions of weed control and management.

American weed control only developed out of the manual methods of pulling and hoeing in the early twentieth century, when salts and other chemicals began to be used as herbicides. However, since the 1970s, as environmental and health concerns have been raised, less toxic methods of weed control have been explored, although it has been found that any interference can have unintended ecological effects. For example, the introduction of a natural predator of an unwanted species—termed "biological control"—can devastate other local species or even, by reducing competition, cause a different species to grow out of control.

Moreover, "weed" has recently developed a new meaning in North America as a term that is applied to socalled invasive species, or non-native plants. Throughout the history of the Americas, as people have immigrated they have tended to bring along the flora and fauna of their homeland, thus intentionally—and at times unintentionally—introducing new species to the continents. Some of these non-native species have multiplied to such an extent that they threaten, or have already destroyed, the biological balance of local environments. This problem has been especially pronounced in Hawaii, Florida, California, and New York State. However, the term "weed" is generally not applied to all introduced or non-native plants but rather to those that are doing the greatest harm to biodiversity and are least controllable through human interference.

Scientists have discovered certain common characteristics among many of the most successful invasive species. They tend to be able to flourish in a variety of climactic zones and to reproduce easily and quickly over long periods with small seeds that are less likely to be eaten. However, non-native plants may also have an advantage in that they can exploit unfilled niches in their new lands while perhaps avoiding traditional enemies. Modern mobility and faster forms of transportation are exacerbating the problem in America and around the world.

Some of the most notorious invasive weeds in America today include kudzu, tumbleweeds, and leafy spurge. Kudzu, from Japan and perhaps originally China, is a semi-woody vine that came to dominate much of the American Southeast in the later twentieth century. Its introduction was encouraged by the American government early in the century to help improve soil and stop erosion, and attempts have continued for decades to undo the ecological damage that its widespread planting and subsequent spread have caused.

Tumbleweeds are now considered to be emblematic of the American West, and some tumbleweed species are indeed native to North America, while others originated in Europe and Asia. They do well with little water and were once cultivated in the hopes of being a food source for livestock. Leafy spurge, which was introduced from Europe and Asia in the early nineteenth century, is believed to be harmful to cattle if eaten. As with kudzu, attempts are being made to control tumbleweeds, leafy spurge, and other invasive weeds through biological, chemical, and manual methods to prevent further environmental and economic damage.

The history of American weeds is not only the story of importations and largely unsuccessful attempts to control non-native species, for native American species have also traveled to new lands. Notoriously, native ragweed, whose pollen causes Americans with hay fever to suffer every fall, has made an appearance in Europe, where it is spreading despite attempts to control it.


Van Driesche, Jason, and Roy van Driesche. Nature Out of Place: Biological Invasions in the Global Age. Washington, D.C.: Island Press, 2000.

Zimdahl, Robert L. Fundamentals of Weed Science. San Diego, Calif.: Academic Press, 1993.

Caroline R.Sherman

See alsoAgriculture .

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Weeds represent the most important pest complex affecting humans throughout the world. In the United States, weeds are estimated to cost the economy more than $20 billion annually. Weeds negatively affect food and fiber production, human and animal health, and the quality of life for the world population. For instance, weeds impact humankind by causing crop failures, triggering allergic reactions, and reducing the esthetic quality of lawns. Interestingly, of the thousands of plant species in the world, less than 250, or approximately one-tenth of a percent, are considered important weeds.

There are a number of definitions for weeds. The Weed Science Society of America in 1994 defined weeds simply as "plants that are objectionable or interfere with the activities or welfare of man." However, an ecological definition describing the characteristics that allow some plants to be weeds is more useful. These characteristics include: the ability to establish in disturbed habitats; the ability to grow and reproduce across a wide range of climatic conditions; seed dormancy; nonspecific germination requirements; rapid growth; high seed production; and unspecialized pollination. Weeds can improve their success by releasing metabolic compounds that interfere with neighboring plants. These compounds are allelotoxins, and the resulting allelopathic response on other plants may represent a future weed management opportunity.

The importance of weeds has resulted in a significant number of herbicides applied worldwide. Further, tillage (soil disturbance) is also a primary tactic used to manage weeds. These strategies may result in soil erosion and herbicides leaching to ground water. However, the benefits of the judicious use of these tactics has resulted in dramatically higher food production and increased agricultural efficiency. Biological control tactics such as using insects or diseases to attack weeds have not been effective in most annual food crops but may hold promise for the future.

see also Allelopathy; Herbicides; Interactions, Plant-Plant; Invasive Species; Kudzu.

Micheal D. K. Owen


Baker, H. G. "The Evolution of Weeds." In Annual Review of Ecology and Systematics, Vol. 5, eds. R. F. Johnston, P. W. Frank, and C. D. Michener. Palo Alto, CA: Annual Review, Inc., 1974.

Bridges, D. D. "Impact of Weeds on Human Endeavors." Weed Technology 8 (1994): 392-95.

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weed / wēd/ • n. a wild plant growing where it is not wanted and in competition with cultivated plants. ∎  any wild plant growing in salt or fresh water. ∎ inf. marijuana. ∎  (the weed) inf. tobacco. ∎ inf. a leggy, loosely built horse. • v. [tr.] remove unwanted plants from (an area of ground or the plants cultivated in it): I was weeding a flower bed. ∎  (weed something out) remove something, esp. inferior or unwanted items or members from a group or collection: we must raise the level of research and weed out the poorest work. DERIVATIVES: weed·er n.weed·less adj.

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Israel abounds in species of weeds, the climatic and soil conditions causing the speedy proliferation of both cultivated plants and weeds. Many of them are *thorns. The prophets frequently warned that because of sin, misfortunes would befall Israel's agriculture and the land would produce weeds in place of cultivated plants. Isaiah in particular warns against the transformation of the sown and planted area into shamir and shayit ("briars and thorns"), a general term for all the species of weeds that flourish among cultivated crops. These weeds start as annual plants, then lowly shrubs grow, and finally the field turns into a forest (cf. Isa. 7). Normally weeds grow in fields of grain in Israel, the most conspicuous being *tares, species of *mustard, Scolymus thistle (ḥo'aḥ), and Ridolfia segetum (boshah, "noisome weeds"). Job (31:40) swears that if he has indeed sinned, then let him be cursed, "Let ḥo'aḥ grow instead of wheat, and boshah instead of barley." The amora Oshaiah observes that it can be deduced from this verse "that a field that produces ḥoḥim is good for wheat, while a field that produces boshah is good for barley" (Tanḥ. B. Deut. 25), showing that these weeds are indications to cultivate plants.


J. Feliks, Olam ha-Ẓome'aḥ ha-Mikra'i (1957), 204–17.

[Jehuda Feliks]

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Weeds ★★★ 1987 (R)

A highly fictionalized account of the career of Rick Cluchey, who, as a lifer in San Quentin federal prison, wrote a play. He was eventually paroled and went on to form a theatre group made up of ex-cons. Original and often enjoyable with a tight ensemble performance. Filmed on location at Stateville Correctional Center in Illinois, with inmates serving as extras. 115m/C VHS . Nick Nolte, Rita Taggart, William Forsythe, Lane Smith, Joe Mantegna, Ernie Hudson, John Toles-Bey, Mark Rolston, Anne Ramsey, Charlie Rich; D: John Hancock; W: John Hancock, Dorothy Tristan; M: Angelo Badalamenti.

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weed A plant in the wrong place, being one that occurs opportunistically on land or in water that has been disturbed by human activity (see ruderal) or on cultivated land, where it competes for nutrients, water, sunlight, or other resources with cultivated plants. Under different circumstances the plant may itself be cultivated (e.g. it may grow from seed or propagate vegetatively from the residue of a previous crop).

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weed2 garment OE.; now chiefly pl. deep mourning apparel, spec. of widows XVI. ME. wēde, repr. two OE. formations:
i. wǣd = OS. wād, OHG. wāt, ON. váð, vóð :- Gmc. *wǣðiz;

ii. OE. (ġe)wǣde = OS. (gi)wādi (Du. gewaad), OHG. giwāti :- Gmc. *gawǣðjam.

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weed1 small plant, esp. one that cumbers the ground. OE. wēod = OS. wiod, rel. to OHG. wiota fern; of unkn. orig.
Hence weed vb. clear of weeds. OE. wēodian. weedy (-Y1) XV.

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weed A plant that occurs opportunistically on land that has been disturbed by human activity (see RUDERAL) or on cultivated land where it competes for nutrients, water, sunlight, or other resources with cultivated plants.