Weed

• Jethro Tull first coined the term weed in 1931 in the book Horse Hoeing Husbandry
• Weeds are the plants, which grow where they are not wanted (Jethro Tull, 1731).
• Weeds can also be referred to as plants out of place.
• Weeds are unwanted or undesirable plants compete with crops for water, soil nutrients, light and space (ie CO₂) and thus reduce crop yields.
• National Research Centre for weed science at Jabalpur (1988).
• Weed is such undesirable plant grown in association with crop which snatches major parts of nutrients, water, light, place, and CO₂ available to the crop. Due to tough competition crop suffers adversely and the production is reduced.
• Followings are the main points
  • Unwanted plant
  • Plant growing where it is not required i.e., a plant out of place
  • Extremely noxious, useless, unwanted, or poisonous plant
  • Any plant or vegetation excluding fungi interfering with the objectives or requirement of people.
  • Thus, weed may be defined as unwanted and undesirable plant which interferes with the utilization of land and water resource and adversely affects human welfare.

Criteria to be a Weed

👉🏻 Whether a plant is weed or not depends upon

• Characteristics and habit of plant
• Relative position
• Time of occurrence of plant Therefore, all plants may become weeds in a particular situation.

Classification of Weed

A. On the basis of site of predominance

A1) Obligate weeds: Such weeds are grown only in association with man and his agriculture. lt is never found in wild form e.g. Chenopodium, Anagallis etc.

A2) Facultative weeds: Such weeds are grown both as wild and in cultivated habitats e.g. Argemone mexicana, Euphorbia hirta.

B. On the basis of Dependence on Host

Parasitic Weed: Weed that depends for its growth on its host plant.

Total Stem Parasite/Holo Stem Parasite

Remember with acronym: CLOS 🤔

• Cuscuta
• Host: Lucerne

  

Semi-Stem Parasite

• Loranthus (Birdvine)
• Host: Mango

  

Total Root Parasite/Holo Root Parasite

• Orobanche
• Host: Solanacous Crops - Tobacco, Chilli, Potato etc., Mustard

  

Semi-Root Parasite

• Striga (Witch Weed)
• Host: Sorghum & Sugarcane

  

  

C. On the basis of Botanical or Morphological Characters

Grasses

Cylindrical and hollow stem having nodes and internodes. Leaf emerges from node, fibrous root, Graminae family e.g., Echinochloa, Phalaris etc. Most of the weeds belong to this group.

Sedges

Triangular stem, no node, very large internode and leaf at top, Cyperaceae family, no branch, usually three leaves at top, pith present e.g., Cyperus (Motha).

Broad Leaf

Broad leaf alternately arranged on stem, cylindrical stem, usually tap root e.g., all dicot weeds like Camellina, Chenopodium album (Bathua).

D. On the basis of Season

Annual

Kharif Weeds: e.g.

• Amaranthus viridis (junglee chaulai)
• Boerhavia diffusa (Vishkhopra)
• Cassia occidentalis (Kasaundhi)
• Euphorbia thymiloia (Chhoti duddhi)
• Euphorbia dracunculoides (Titali)
• Digera arvensis (Lahsua)
• Datura festoosa

Rabi Weeds: e.g.

• Convolvulus arvenis (Hiran Khuri)
• Chenopodium album (Bathua) ^{UPPSC 2021}
• Argemone Mexicana (Satyanashi)
• Anagallis arvenis (Krishna nil)
• Desmodium trifolium (Tinpatia)
• Cuscuta reflexa
• Asphodelus tenuifolius (Vanpyaji)
• Parthenium hysterophorus: Congress Grass/Carrot Grass/Gajar Grass (King of Weeds)

Biennial

• Dacus carota
• Cirsium vulgare
• Alternanthera pungens
• Eichornia intybus

Perrenial

• Cyperus rotundus (Motha)
• Cynodon sp. (Dub grass)
• Saccharum spontanium
• Ageratum conizoids
• Achyranthus
• Zyziphus rotundifolia

E. Aquatic Weeds and Submersed Weeds

• Submerged Weeds: Weeds grow under water e.g., Hyrilla

• Emerged Weeds: Anchored weeds growing in water with major foliage on the above surface e.g., Nilumbium speciosum

  

• Marginal Weeds: Weeds grown mostly in shoreline areas with a depth of 60-90 cm water e.g., Typha sp., Polygonum sp.

  

• Floating Weeds: Weed leaves float on water surface either single or in cluster e.g., Echhornia crassipes (Water Hyacinth), Salvinia, Pistia (water cabbage), Nymphaea sp., etc.

  

  👉🏻 Eichornia cressipes is known as weeds of fisherman.

  

  

  

👉🏻 For control of aquatic weeds 2, 4 - D and Copper Sulphate is used.

F. Other Basis

• Relative Weed e.g. Rice in Wheat field.
• Absolute Weed e.g. Such weeds are due to its characteristics e.g. Cyperus rotundus.
• Rogue: The off type crop variety in the field of certain crop variety is called rogue.
• Mimicry Weeds: Such weeds are similar in external morphology with the crop e.g. Phalaris in wheat field and wild rice in the rice field.
• Volunteer Weeds: Such weeds are grown from the fallen seeds of previous or preceeding crop in the field.
• Noxious Weeds: Such weeds are declared undesirable, troublesome weed difficult to control e.g. Parthenium sp.
  • Prohibited Noxious: Perennial weeds reproduce by the seeds, underground roots, stems or other parts and difficult to control.
  • Restricted Noxious: Perennial weeds objectionable in cropping areas but can be controlled. Ex. Parthenium hysterophorus
• Objectionable Weed: Problematic weed, whose seed once mixed with crop seed is extremely difficult to control/separate. E.g., Convolvulus arvensis & Phalaris in wheat and wild rice in rice field.
• Satellite Weed: Weed that become an integral part of the crop ecosystem.
• Most problematic weeds are Salvinia molesta, Cyperus rotundus, Cynodon dactylon, Echinochloa colona, Sorghum helepense etc.
• Salvinia molesta is the world’s worst weed.

Exotic/Alian Weeds

• Parthenium hysterophorus – Introduced from USA
• Phalaris minor come in India in 1960.
• Lantana camara – Sri Lanka
• Tribulus terrestris – Mediterranean region
• Eichornia cresipes

Weed

• Jethro Tull first coined the term weed in 1931 in the book Horse Hoeing Husbandry
• Weeds are the plants, which grow where they are not wanted (Jethro Tull, 1731).
• Weeds can also be referred to as plants out of place.
• Weeds are unwanted or undesirable plants compete with crops for water, soil nutrients, light and space (ie CO₂) and thus reduce crop yields.
• National Research Centre for weed science at Jabalpur (1988).
• Weed is such undesirable plant grown in association with crop which snatches major parts of nutrients, water, light, place, and CO₂ available to the crop. Due to tough competition crop suffers adversely and the production is reduced.
• Followings are the main points
  • Unwanted plant
  • Plant growing where it is not required i.e., a plant out of place
  • Extremely noxious, useless, …

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