weed killer: see herbicide.

weed, common term for any wild plant, particularly an undesired plant, growing in cultivated ground, where it competes with crop plants for soil nutrients and water. In their natural habitat, wildflowers and herbs not only provide beauty but function in many useful ways, e.g., as a source of food for insects and animals and to enrich the earth, loosen hard-packed soils, and help prevent erosion. However, when they invade cultivated areas they often interfere with the desired crop by appropriating space, sunlight, moisture, and soil nutrients. Weeds may also harbor and spread insect and fungus pests. Dried weeds along roadsides are often the starting point for brush and forest fires. Their habits of growth and of propagation must be considered in attempting to eradicate them. Control methods include continual soil cultivation, blanketing the soil with some material (e.g., mulch) to thwart weed growth, and the use of various herbicides (see spraying). Plants which are cultivated in one region may become weeds when introduced in another, e.g., the oxeye daisy, imported to the United States from Europe; the Russian thistle, called tumbleweed in America; and burdock, which in Japan is grown as a vegetable. Crabgrass and ragweed are weeds well known to gardeners and to hay-fever sufferers.

rattlesnake weed: see hawkweed.

joe-pye weed, name for a tall North American plant (Eupatorium purpureum) of the family Asteraceae (aster family), having small, usually pinkish-purple blossoms in large terminal clusters. The name comes from that of a Native American who reputedly effected many cures with the herb. An infusion of the leaves and roots was formerly, and is sometimes yet, employed as a diuretic and an astringent, among other things. It is also called gravelroot, trumpetweed, and purple boneset or thoroughwort. Two related species, E. maculatum and verticillatum, are also called joe-pye weed. Joe-pye weed is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

dyer's-weed, name for any of several plants from which dyestuffs are obtained. They include a mignonette, a broom, and species of goldenrod.

butterfly weed: see milkweed.

Weed, Thurlow, 1797-1882, American journalist and political leader, b. Cairo, N.Y. After working on various newspapers in W New York, Weed joined the Rochester Telegraph and was influential as a supporter of John Quincy Adams. For a short time he published the Anti-Masonic Enquirer and as a leader of the Anti-Masonic party opposed Martin Van Buren. He wielded much political influence as editor of the Albany Evening Journal after 1830 and was a staunch opponent of the Albany Regency. Becoming a Whig, Weed in 1840 helped secure the election of William H. Harrison as President. In 1844 he helped bring about the presidential nomination of Henry Clay, and in 1848 he backed Zachary Taylor. Though paying lip service to various reforms, notably the abolition of slavery, Weed was more at home with the problems of patronage and lobbying and came to be regarded as the silent boss of the Whig party. After the Whig party disintegrated over the slavery issue, Weed joined (1855) the new Republican party and worked in close cooperation with William H. Seward. Seward was his close personal friend as well as political ally, and Weed carefully shepherded Seward's career as state legislator, governor of New York, and U.S. senator. He failed, however, to secure for Seward the Republican presidential nomination in 1860. Both Weed and Seward nevertheless came to be President Lincoln's staunch supporters. During the Civil War, Weed went on a special diplomatic mission to France and England. His political power in the Republican party was destroyed by his support of the Reconstruction policies of Andrew Johnson in 1866, and he was never again able to exert great political influence. His travels were turned to account in his Letters From Europe and the West Indies (1866).

Jimson weed or Jamestown weed, large, coarse annual plant (Datura stramonium) of the family Solanaceae (nightshade family), native to warm-temperate and tropical regions of the New World, but long widely distributed and often weedy. This and other species of the genus contain a narcotic poison, stramonium, similar to that of the related belladonna, that has been used by many peoples for various purposes, e.g., as a medicine (now chiefly inhaled for the relief of asthma or applied externally as a painkiller) and in the past as a poison and an instrument for obtaining prophetic dreams or messages in various tribes. The amusing antics of soldiers in colonial Virginia who ate Jimson weed have been recorded for history. Stramonium, comprised of several alkaloids (e.g., scopolamine, atropine, and hyoscyamine), may also be obtained from some other species of Datura. Scopolamine is used as a sedative. Jimson weed is classified in the division Magnoliophyta, class Magnoliopsida, order Polemoniales, family Solanaceae.

Jamestown weed: see Jimson weed.

Any plant growing where it is not wanted. On land under cultivation, weeds compete with crops for water, light, and nutrients. On rangelands and in pastures, weeds are those plants that grazing animals dislike or that are poisonous. Many weeds are hosts of plant disease organisms or of insect pests. Some originally unwanted plants later were found to have virtues and came under cultivation, while some cultivated plants, when transplanted to new climates, escaped cultivation and became weeds in the new habitat.

Learn more about weed with a free trial on Britannica.com.

North American plant (Asclepias tuberosa) of the milkweed family, a stout, rough-haired perennial with long horizontal roots. The leafy, erect, somewhat branching stem is about 1–3 ft (0.3–0.9 m) tall. In midsummer it bears numerous clusters of bright orange flowers. Unlike most milkweeds, it has a scanty milky juice. It is native to dry fields and is often planted in wild gardens or grown as a border plant.

Learn more about butterfly weed with a free trial on Britannica.com.

(born Nov. 15, 1797, Cairo, N.Y., U.S.—died Nov. 22, 1882, New York, N.Y.) U.S. journalist and politician. He worked on various newspapers in upstate New York and was a leader in the Anti-Masonic movement. He was the founding editor of the Albany Evening Journal (1830–63). He helped form the Whig Party in New York and was instrumental in William Seward's election as governor (1838) and in the presidential election of William H. Harrison (1840). He later became active in the Republican Party and was a staunch supporter of Pres. Abraham Lincoln. In 1861 he was sent to England to seek support for the Union.

Learn more about Weed, Thurlow with a free trial on Britannica.com.

(born Nov. 15, 1797, Cairo, N.Y., U.S.—died Nov. 22, 1882, New York, N.Y.) U.S. journalist and politician. He worked on various newspapers in upstate New York and was a leader in the Anti-Masonic movement. He was the founding editor of the Albany Evening Journal (1830–63). He helped form the Whig Party in New York and was instrumental in William Seward's election as governor (1838) and in the presidential election of William H. Harrison (1840). He later became active in the Republican Party and was a staunch supporter of Pres. Abraham Lincoln. In 1861 he was sent to England to seek support for the Union.

Learn more about Weed, Thurlow with a free trial on Britannica.com.