About 350000 species of plants are known to man .Of these less than 1% or about 3000 have economic value and only about 300 species are currently used for food and feed.

Some plants are termed “weeds” but apparently not under all circumstances.

For instance Burmuda grass ( Cynodon dactylon) is a valueable grass in pastures,but a very troublesome weed in crop foields.

One 250 years old definition of a weed reads “a weed is a plant growing where it is not desired”

A more relevant definition is “ Weeds are plants growing in places where, and at times when, man wants either some other plants to grow or no plants to grow atall”

weeds are defined as those alien plant species which are listed

as “noxious”

Weed, plant growing where human beings do not want it to grow

Noxious weed” means an alien plant or parts of an alien plant that have been designated by

rule as being noxious or has been declared a noxious weed by a local advisory board, and

meets one or more of the following criteria: · Aggressively invades or is detrimental to

economic crops or native plant communities; · Is poisonous to livestock; · Is a carrier of detrimental insects, diseases, or

parasites; · The direct or indirect effect of the presence of

this plant is detrimental to the environmentally sound management of natural or

agricultural ecosystems

Competition for mineral nutrients. Competition for sunlight. Competition for water. Competition for space Parasitism. Increase incidence of pests and diseases. Reduction of crop quality Interferences with cultivation and harvest

operations. Clogging of irrigation and drainage canals.

Crop Loss in yield

Wheat 2-30%

Maize 20-40%

Rice 20-83%

Sugarcane 10-35%

Oilseeds 10-50%

Vegetables 40-80%

There are many ways on which weeds can be classified into groups for convenience of planning,interpreting and recording control measures against them. Some important classification of weeds used by weed researchers in world for different purposes are as follows:

Classification according to anatomy of weeds: Depending upon their cycle, weeds can be classified as

Annual Biennials Perennials

Annual weeds: Annual weeds more commonly complete their life cycle in one season. An annual weeds can be either

Summer annuals Kharif annuals e.g. foxtail Winter annual e.g. lambs quarter

Biennial weeds complete their life cycle in two years in the firs year they remain vegetative, and in the second year they produce flowers and set seeds.

E.g. Daucus, Carota, Nulicaulis, etc.

Perennial weeds grow for three or more years.

E.g. Shallow rooted perennials – Bermuda grass, Quack grass

Deep rooted perennials :Johnson grass

a. Monocots b. Dicots

Depending upon the development of bark tissues on their stems and branches, weed can be classified as :

a. Woody e.g Lantana b. Semi-woody and c. Herbaceous species

It is classified into three classes: Season bound, b. Crop bound, c Crop associated

Depending upon their occurrences there can be nine important groups of weeds.

Crop-land weeds. Falloland weeds. Grassland or pasture weeds. Non-cropland weeds Aquatic weeds Forest and woodland woods Lawn and garden weeds. Weeds of plantations. Orchard and vineyard weeds

Many of weeds in India originated in some other part of the world. For e.g. Convolvulus sp –Eurasia, cyperus –Euphorbia,-Europe, Lantana –Africa

Of the several variable of soil, soil pH is implicated most frequently with the distribution of weed species. Weeds, such as red sorrel, corn sporry and bracken tend to comminute with weed flora on saline and alkali soils.

Temperature, rainfall, air quality, humidity and solar energy have pronounced effect on the distribution of weeds. One could classify weeds as

hillside weeds, weeds of plains, temperate weeds, tropical weeds,etc.

Facultative weeds are those weeds that grow primarily in wild communities but often escape to cultivated fields. E.g. Opuntia Spp. Obligate weeds on the contrary, occur only in cultivated or otherwise disturbed land.

For e.g.: Field bind weed.

Noxious weeds is a plant arbitrarily defined as being especially undesirable troublesome and difficult to control for e.g. Chicory, thistle, bermuda grass (hariyali

Annual grasses Perennial grasses Broadleaf weeds Miscellaneous

Goosegrass Eleusine Indica Rabgrasses Digitaria spp. annual bluegrass Poa annua yellow foxtail Setaria lutescens (glauca)

It is a warm season annual member of the Grass family (Poaceae) that reproduces by seeds, usually emerging a few weeks after crabgrass. Goosegrass is a coarse, bunch-type grass that forms a basal rosette of prostrate to occasionally upright flattened stems up to 2 feet long. The stems do not root at nodes. The root system is fibrous, and the lower portions of stems near the base are silver or white. The leaves of goosegrass are dark green, hairy near the base, and smooth and keeled below. They grow up to 12 inches long and 1/3 inch wide and are either flat or folded. Goosegrass flowers are 2 to 10 flattened, finger-like spikes that each resemble a zipper

It is a warm season annual member of the Grass family that reproduces by seeds. Seeds germinate at temperatures between 68 and 95 °F. Yellow foxtail forms a coarse, upright or prostrate, bunch-type grass. It usually branches at the base and may root at lower nodes. Growing up to 4 feet tall, yellow foxtail emerges from a shallow, fibrous root system and normally has flattened stems that are reddish near the base. Leaves of yellow foxtail are flat, smooth, and with margins that are somewhat rough.

Quackgrass Agropyon repens creeping bentgrass Agrosis palustris tall fescue Festuca undinacea Nimblewill Muhlenbergia shreberi

common yarrow Achillea millefolium wild garlic Allium vineale shepherd's purse

Capsella bursa-pastoris

mouse-ear chickweed Cerastium vulgatum Thistles Cirsium spp. prostrate spurge Euphornia supina ground ivy Gleochoma hederacea Henbit Lamium amplexicaule roundleaf mallow Malva neglecta black medic Medicago lupulina

yellow woodsorrel Oxalis strictabroadleaf plantainPlantago major

buckhorn plantain Plantago lanceolata prostrate knotweed Polygonum aviculare common purslane Portulacea oleracea red sorrel Rumex acetosella curled dock Rumex spp. common chickweed Stellaria media Dandelion Taraxacum Officinale white clover Trifolium repens Violets Viola spp

Also known as milfoil, thousandleaf, or woundwort, it is a perennial member of the Aster family (Compositae) that reproduces by seeds or short underground rootstocks. Upright common yarrow stems emerge from taproots to form a dense mat under close mowing. The stems are usually not branched; are smooth to densely covered with long, soft or woolly grayish-green hairs and are 4 to 24 inches tall. The tops of the stems may branch. The alternate, finely pinnately dissected and fern-like leaves are soft and covered with hair. The basal leaves longer than those growing on stem; stem leaves are 3 to 8 inches long. The flowers develop in falt-topped clusters at the top of branches. There are white or pink ray flowers and yellow disk flowers. Flowering occurs in June to October. Common yarrow often occurs in poor, gravely, droughty, and infertile soils and does not compete well with turf on rich soils. It is wear and drought tolerant

It is a cool season perennial member of the Lily family (Liliaceae) that reproduces by seeds, aerial bulblets, and

underground bulblets. Most reproduction in northern states is asexual. Beginning growth early in the spring, wild garlic develops from a bulb into an upright, grass-like plant with an onion or garlic odor. Stems can grow to more than 3 feet. The leaves of wild garlic are 2-ranked, slender, hollow, nearly round; and attached halfway down on waxy stem. The inflorescence is an umbel, 1 to 2 inch diameter. The flowers are small, greenish-white, and found on stems above the aerial bulblets.

Flowering occurs during May and June. Wild garlic is commonly found in poorly-drained, fine-textured, fertile soils and thin turf areas

It is a annual or winter annual member of the Mustard family (Cruciferae) that reproduces by seeds. Shepherd's purse emerges from a thin, branched taproot to form a rosette of leaves and thin, erect, usually branched stems to 24 inches tall. The stems are usually covered with grayish hairs. Forming a rosette, the basal leaves are simple, 2 to 5 inches long, and variably lobed, serrated, or divided. Leaves on the stems are alternate, 1 to 4 inches long, and are usually toothed or lobed. The base on these leaves are ear-like and clasp or rap around the stem.

It is a perennial member of the Pink family (Caryophyllaceae) that reproduces by seeds and occasionally by creeping stems that may root where they touch the soil. Mouse-ear chickweed have shallow, fibrous roots. The mat-forming plants grow up to 20 inches tall and have weak, hairy, spreading stems. Mouse-ear chickweed leaves are opposite, dark green, very hairy, and less than 1 inch long and up to 1/2 inch wide. They are without petioles and oval to elliptically shaped. The small, white flowers have five white petals that are notched at the tips. Hairy, leafy sepals are borne beneath the flowers which occur April through July.

They are members of the Aster family (Asteraceae). Bull thistle is a biennial that reproduces by seed, and Canada thistle is a perennial that reproduces by seed and rhizomes. Bull thistle forms large, coarse plants with spiny leaves, large taproots, and stems that are heavy and branched at top and hairy when mature. Canada thistle also forms large, coarse plants with spiny leaves. The large, rhizomatous underground system form stems that are grooved and branched at top, hairy in youth, smooth when mature. Bull thistle leaves are deeply-lobed, spiny above and below, and pubescent beneath. The leaf base joins stem resulting in winged appearance

It is a warm season member of the Spurge family (Euphorbiaceae) that reproduces by seeds. Germination occurs when soil temperatures warm to 60 to 65 oF and can continue as soil temperatures climb to more than 90 oF. Prostrate spurge develops a central taproot from which prostrate stems that form a flat, extensively branched mat up to 2 feet in diameter. The stems exude milky sap when broken. Leaves of prostrate spurge are opposite, small, oval, and up to 3/5 inch long. They are sometimes purple-spotted and/or hairy. The petioles are short. Prostrate spurge flowers are very small and inconspicuous

Also known as creeping Charlie, it is a perennial member of the Mint family (Lamiaceae) that reproduces by seeds and root pieces. It may form patches in turf as it creeps on square stems that can grow up to 2 1/2 feet long, sometimes rooting at the nodes. Occasionally the stems grow in an ascending fashion. Leaves of ground ivy are opposite, round to kidney shaped, and 1/2 to 1 1/2 inches in diameter.

It is also known as common mallow, cheeses, dwarf mallow, running mallow, malice, round dock, and button weed. It is an annual or biennial member of the Mallow family (Malvaceae) that reproduces by seed. Emerging from a short, straight taproot, roundleaved mallow develops stems up to 12 inches long. The hairy stems are horizontal or upright and may be branching at base. The stems do not root as they touch the ground. The simple, alternate leaves of roundleaved mallow are round to heart-shaped usually with 5 to 9 shallow lobes or rounded teeth. They are up to 2 1/2 inch across and hairy on both surfaces. The petioles are also hairy and up to 4 inches long.

It is an annual, biennial or perennial member of the Legume family (Fabaceae) that reproduces by seeds. Black medic is shallow rooted with multi-branched slender, prostrate, slightly hairy stems spreading 12 to 24 inches. The alternately arranged, dark green leaves are compound with three, oval leaflets. The center leaflet is stalked and the side leaflets occur close to the stem. Leaves are sparsely hairy and the leaflets 1/5 to 3/5 inch long. The 1/8 to 1/6 inch long bright yellow flowers are clustered on short stems that emerge from the leaf axils. Each cluster is approximately 1/2 inch long, round, and comprised of up to 50 individual flowers. Flowering occurs April to October

It is also known as knotgrass. It is a warm season member of the Polygonaceae (Buckwheat Family) that reproduces by seeds. During early spring, knotweed resembles a grass with long, dark green leaves when germinating. Later, it forms a flat mat up to 2 feet in diameter. It has slender, wiry stems; and emerges from a taproot. There are papery sheaths at each node that give stems a knotted or swollen appearance. The leaves are alternate, small, narrowly oval, dull bluish-green, and up to 1 1/4 inches long and 1/3 inch wide. Its flowers are small, borne in clusters in leaf axils. The buds are purplish opening to white to yellow flowers during June through October

It is also known as wild portulaca. It is a warm season annual member of the Purslane family (Portulacaceae) that reproduces by seeds or rooting stem pieces. Common purslane emerges from a heavy taproot, to develop succulent, smooth, fleshy stems that are usually purple-red and may root at lower nodes. these many branched stems reach up to 24 inches long and grow in a prostrate fashion to form mats. Common purslane leaves are alternate to sub opposite, oval shaped with the widest point beyond the leaf's middle. Growing up to 1 1/4 inch long, the thick, fleshy leaves are often clustered near the ends of branches. They are smooth and without leaf stalks. The yellow flowers of common purslane are borne individually in the leaf axils or clustered at end of branches. There are five petals. The fruit is a globular capsule. Flowering occurs in July through September.

It is a perennial member of the Buckwheat family (Polygonaceae) that reproduces by seeds and occasionally root pieces. Curled dock develops a dense rosette of 6 to 12 inch-long leaves that emerge from a large, fleshy, somewhat branched yellow-orange taproot on a short crown. At flowering, the inflorescence develops at the top of a stem that can reach 4 1/2 feet tall. The dark green leaves are simple with a heart-shaped base. The leaf edges are wavy or curly. Leaves on the stem are alternate and have short petioles.

It is a cool season perennial of the Aster family (Asteraceae) that reproduces by seeds and root pieces. Dandelions emerge above a long, sturdy taproot to form basal rosettes of narrow, deeply lobed leaves. These leaves are 2 to 10 inches long and up to 2 1/2 inches wide. They have jagged lobes that point back towards stem. Dandelion inflorescences are yellow, up to 2 inches in diameter, and appear to be solitary. They are borne on hollow stems that can grow up to 20 inches long, and held above the foliage. The inflorescences ripen to become round "puffballs" of wind-dispersed seeds. Flowering period is from early spring to late fall. Dandelions occur in most lawns throughout the growing season, especially thin turf areas

Weed Description: A perennial trailing or climbing weed with white morningglory-like flowers that may reach 3 1/3 feet in length. Field bindweed is primarily a weed of nurseries, agronomic crops, and fencerows that can be found throughout the United States Weed Description: A perennial trailing or climbing weed with white morningglory-like flowers that may reach 3 1/3 feet in length. Field bindweed is primarily a weed of nurseries, agronomic crops, and fencerows that can be found throughout the United States

yellow nutsedge Cyperus esculentus

Also known as yellow nutgrass. It is a perennial member of the Cyperaceae (Sedge Family) that reproduces by seeds and tubers (nutlets) that form at ends of rhizomes. Individual yellow nutsedge plants have upright, grass-like leaves that emerge from a fibrous root system and scaly rhizomes. These leaves emerge from the plant's base, are 3-ranked, grass-like, and light yellow-green. They are 1/8 to 1/2 inch wide, up to 3 feet long, and have parallel veins with a prominent midvein

S.no Botanical name Local names1. Cyperus rotundus Nut grass, purple nutsedge2. Cyondon dactylon Bermuda grass, couch grass,star

grass3. Echinochloa crusgalli Barnyard grass4. Echinochloa colonum Awnless barnyard grass5. Eleusine indica Crowfoot grass, goosegrass,

wild finger millett, 6. Sorghum halepense Aleppograss, jhonson grass7. Imperata cylindrica Sword grass, cogon grass.

8. Eichhornia crassipes Wateryhyacinth

9. Portulaca oleracea Pigweed purslane

S.no Botanical name Local names10. Chenopodium album Fathen, goose foot,

lambsquarter11. Digitaria sanguinalis Hairy or large crab grass.12. Convolvulus arvensis Bind weed, field bind weed13. Avena fatua Wild oats14. Amaranthus hybridus Pigweed, smooth amaranthus15. Amaranthus spinosus Prickly amaranth, spiny

pigweed16. Cyperus esculentus Nuttgrass, water grass, yellow

nutsedge.17. Paspalum conjugatum Sour grass, sour paspalum

18 Rottboellia exaltata Guinea foelgrass, itch grass, Raoul grass

# Weed species English name Average number of seeds per plant

1. Amaranthus hybridus

Pigweed, smooth amaranthus

196000

2. Chenopodium album Fathen, goose foot, 72000 lambsquarter

3. Cascuta species Ddder 160004. Eleusine indica Crowfoot grass,

goosegrass, wild finger millett,

41200

5. Portulaca oleracea Pigweed purslane

193000

Name of weed

English name Viability of some weed seeds in years

Stellaria media

Common chick weed

30

Capsella bursa pastoris

Shepherds purse

35

Chenopodium album

Rough pigweed 40

Rumex crispus

Curled dock 80