Classification of Weeds
There are over 30,000 species of weeds round the world. Out of these about 18,000 are known to cause serious losses. In the list of world’s worst weeds nutsadge (Cyperus rotundus) ranks first and hariali (Cynodon dactylon) second position.
The weeds with similar morphological characters, life cycle, requirements of soil , water, climatic condition etc are grouped together as a class or category. Therefore classification of weeds is helpful for adopting weed management methods for particular group of weeds instead of against an individual weed species. It is always economical and practically feasible to manage the group of weeds as compared to manage the individual weed species.
I) Classification of Weeds According to Life Cycle:
Depending upon their life cycle weeds can be classified as
1) Annual Weeds:
They complete their life cycle within one year or one season.
a) Kharif Annuals / Kharif Weeds:
They appear with the onset of monsoon (June, July) and complete their life cycle when rainy season is over (Oct or Nov) E.g Cock’s comb, dudhi, math, chimanchara , parthenium etc.
b) Rabi Annuals / Rabi Weeds:
They complete their life cycle during winter season ( Oct/Nov to Feb) E.g Vasanvel ( Chenopodium album) , Ghol ( Portulaca oleracea), wild oat etc.
c) Summer Annuals / Summer Weeds:
They complete their life cycle during summer season ( Feb to May), Majority of the Kharif seaosn weeds grow during summer season in irrigated farming E. g Parthenium , Amaranthus spp. Euphorbia Spp. ( Dudhi) etc.
The short- lived annual weeds are called ephemerals E. g Niruri ( Phyllanthus niruri). These weed completes its life cycle within a very short period of 2 to 4 weeks.
2) Biennial Weeds:
They take at least two years or two seasons to complete their life cycle. They complete their vegetative growth in first year or season and produce flowers and seeds in the next year or season. E.g Wild carrot- ( Daucas carota), wild onion – ( Asphodelus spp) , Jangli gobhi- (Launea spp).
3) Perennial Weeds:
They continue or grow for more than two years or several years. Perennial weeds are further classified as.
II) According to Root System:
Depending upon the depth of root system perennial weeds are classified as
a) Shallow Rooted Perennials:
Those perennial weeds having about 20 to 30 cm deep root system are called shallow rooted perennial weeds.
E. g Hariali ( Cynodon dactylon), Quack grass ( Agrophyron repens).
b) Deep Rooted Perennials:
Weeds having about one meter or more deeproot system. E.g Nutgrass ( Cyperus rotundus), Johnson grass ( Sorghum holepense ), Acacia spp. wild ber etc.
III) According to Mode of Reproduction:
a) Simple Perennials: Reproduce mostly by seeds.
E. g Ghaneri- Lantana camara) Acacia- ( Acacia spp),
Wild Ber- ( Zizyphus spp).
b) Bulbous Perennials:
Propagate by underground parts like bulbs, rhizomes , tubers etc, as well as seeds.
E .g Cattail ( Pan kanis) (Typha spp),
Nut grass or Nut sedge ( Cyperus rotundus),
Johnson grass (Sorghum halepense).
c) Creeping Perennials:
Spread by lateral extension of the creeping above ground stem or roots or by seeds.
E .g Hariali – (Cynodon dactylon), Ambooshi – ( Oxalis litifolia)
IV) According to the Place of Occurrence (Habitat):
Depending upon the place of their occurrence they can be grouped as under:
1) Weeds of cropped lands: E. g Chandvel, Striga, Orobanche, Wild rice etc.
2) Weeds of Pastures and grazing lands: E. g Parthenium, Hulhul (Cleome viscose).
3) Weeds along water channel: E .g Jalkumbhi ( Eichhornia crassipes) Pandhari Phuli ( Lagasca mollis).
V) According to Nature of Stem:
1) Woody Weeds:
These are the woody and semi-woody and semi-woody rough stem shrubs and are collectively called brush weeds, E .g Acacia wild ber, Ghaneri (Lantana Camara) etc.
2) Herbaceous Weeds:
These weeds have green and succulent stem and common accurence on farm lands. E.g Math, Cocks, Comb, Dudhi, Parthenium etc.
VI) According to the Origin of Weeds:
1) Introduced or Exotic weeds/ Allien Weeds or Anthrophytes
Many weeds move from the place of their origin by seeds or other parts to a new area and establish there and become introduces weeds such introduced weeds are called alien weeds or anthrophyes.
E .g 1. Parthenium hysterophorus –From U.S.A
2. Solanum elaegnifolium- With food grain.
3. Lantana camera ( Ghaneri) : From Shri-Lanka by birds.
4. Cockleber / Gokhru (Xanthium strumarium) : Native of America.
5. Orobanche spp. ( Bambakhu)- Europe.
6. Nutgrass ( Cyperus rotundus) chandvel: Eurasia.
7. Water hyacinth – Tropical America ( Introduced in India by Portuguese)
8. Johnson grass- Asia and southern Europe.
2) Indigenous Weeds:
Origin of majority of tropical weeds is India E .g Cock’s comb, Dudhi, Aghada, Hariali etc.
VII) Facultative Weeds or Apophytes:
Weeds which grow primarily in undistributed or close communities but may some times escape to the cultivated fields, It is also called Apophytes E .g Cactus.
VIII) Obligate Weeds:
Weeds which grow or occur primarily in cultivated field where the land is distributed frequently. E.g Chandvel ( Convolvulus arvensis).
IX) Noxious Weeds:
The weeds which are undesirable , troublesome and difficult to control are called noxious weeds E.g Nutgrass, Hariali, Parthenium , Striga, Orobanche, Water hyacinth etc.
X) Objectionable Weeds:
Weeds which produce seeds that are difficult to separate once mixed with crop seeds are called objectionable weeds. E. g The mixture of Argemone Mexicana (Pivala Dhotra) seeds in mustard. Wild onion in cultivated onion.
XI) Industrials Weeds:
Weeds invading areas around buildings, highway, railway lines, fence rows, electric and telephone pole bases etc are called industrial weeds. E .g Parthenium, Reshimkata, Katemath, etc.
XII) Poisonous Weeds:
E.g. Parthenium, Datura, Poison, ivy ( Rhus sp), etc.