Classification Of Weeds

  CLASSIFICATION OF WEEDS

“A weed is a plant growing where it is not desired. A plant could be undesirable at one place and desirable or of little concern at the other”

“ A weed is a plant considered undesirable in a particular situation, a plant in a wrong place

CLASSIFICATION OF WEEDS

1)    ANNUAL WEEDS: - Annuals weeds grow and mature within a year of their germination, but more commonly they complete their life cycle in one season.

A.    Summer annuals: Trianthema spp. and Digera arvensis

Summer annual weeds grow, flower, produce seed and are killed by frost during the fall season.

B.    Winter annuals :- Chenopodium album. A

  Winter annuals weeds are annual weeds germinate in the fall and winter and grow actively in spring

Ø A weed like Amaranthus viridis may grow round the year near irrigation channels and other moist places, but primarily it is a summer annual plant. A weeds like Phyllanthus fratenus ‘Niruri’ completes its seed to seed cycle within two or four weeks. Such short – lived annuals are called Ephemerals.

General Characteristics:-

1.    Annual weeds reproduce by abundant seed production, however some like  Allium  Spp. wild onion and wild garlic may grow also  from bulbs and bulbils.

2.    They fail to re-grow when they are cut close to the ground level. These are  known as Simple annuals.

3.    Several annual weeds possess crown buds which sprout into new shoots  soon  after the mother plant is de-topped.

4.     Easy to control. Such weeds must be destroyed before they set seeds.

5.    Annuals weeds usually produce thousands of seeds on each plant. Buried in  soil by deep tillage. These weed seeds can remain dormant for several years.  This makes weed eradication almost infeasible. Therefore, a farmer must be  particular about not allowing the weeds to set seeds on his land.

2.BIENNIAL WEEDS: Launaea nudicaulis

Ø They complete their life cycle in two years; in the first year they remain vegetative and in the second year they produce flowers and set seeds.

Ø The usual feature of biennial weeds to flower in the second year of growth limits their dispersal through seeds very much.

Ø It is so because they get harvested along with the crop plants before they get a chance to set seeds. The biennial weeds must be controlled in the first year of growth before these have a chance to store food in their roots.

     

3.PERENNIAL WEEDS

They grow for 3 or more years. 

Ø Usually, perennials weeds flower for the first time in the second year of their growth and thereafter flower each year regularly.

Ø Besides seeds, they reproduce vegetative from underground specialized organs.

Ø In tropical areas these remain green throughout the year although in subtropical regions they may undergo dormancy during the low temperature periods.

Depending upon the depth of their underground growth the perennial weeds may further be classified as:-

1.)Shallow rooted perennials: - eg. Cynodon dactylon

        

     Their roots and rhizomes are limited mainly to the furrow slice depth of soil.

2.)Deep rooted perennials: - e.g. Cyperus rotundus

  Deep rooted perennials perennials weeds are also called perecious weeds.

Ø The control of perennial weeds is much more difficult than that of annuals since neither tillage nor the present day selective herbicides can reach their deep roots and underground modified shoot systems. Therefore, attempts to suppress such weeds are usually made during the fallow seasons by deep summer tillage along with the application of herbicides.

 

CLASSIFICATION ACCORDING TO COTYLEDON:

Ø Monocots :- Also known as narrow leaf or grass weeds

eg. Cynodon dactylon. 

 Dicot :- Also known as broadleaf weeds , Two exceptions to this are sedges and cattails which although narrow leaved, are not grasses. They belong to the family Cyperaceae and Typhaceae, respectively. e.g. Digera arvensis             

                     

 

CLASSIFICATION BASED ON NATURE OF STEM:

·       Its Depending upon development of bark tissue on their stems and branches

Ø Woody and Semi Woody weeds:- Include shrubs and under-shrub and are  collectively called brush weeds. Lantana camara, Acacia arabia, Prosopis  juliflora and Zizyphus rotundifolia are the examples of brush weeds.

Herbaceous weeds:- In variance with woody and semi-woody, herbaceous weeds have green, succulent stems and are of most  common occurrence around us Amaranthus viridis, and Chenopodium  album are the examples of herbaceous weeds. 

        

 

 

CLASSIFICATION BASED ON ASSOCIATION

 

1.)Season bound weeds: - It grows in specific season of the year with disregard to the crop species cultivated. These weeds may be either summer annuals or winter annuals. In the case of perennial weeds the period of their major vegetative growth is taken as their growing season, e.g. Sorghum halepense is a summer perennial weed, whereas,  Cirsium arvense is a winter perennial weed.

 2.)Crop- Bound weeds:- These are usually parasitic weeds. They depend for  their survival upon their host plants partially or fully. Cuscuta spp.  Orobanche spp. and Striga spp. are   the most common crop bound  weeds.

3.)Crop associated weeds:-Such weeds grow along with the crops. These are also crop specific but they may be  associated with certain crops for one of the following reasons: 

(a) Need for specific micro climate:- Weeds like Cichorium intybus requires a for their best growth shady, cool and moist habitat which is amply available in crops like lucerne and berseem.

(b) Mimicry:- Wild rice in paddy field, Wild oat and Canary grass (Phalaris spp.) in small grain crops survive because of their similarity in morphology with host crops. This mechanism is called mimicry. A weed like wild oat tends to grow to the height of winter grains and adjust its ripening time to the crop over a wide varietal range. This kind of mimicry is called phenotypic mimicry.

(c) Ready contamination of crop seeds with weed seeds. Allium spp., Wild garlic and P. minor mature their seeds at the same height and time as winter grains and thus they easily contaminate crop seeds at harvest.

 

CLASSIFICATION ACCORDING TO HABITAT

1.   Crop land weeds - Digera arvensis               

2.    Fallow land weeds – Zizyphus rotundifolia

 3.  Grassland, Pasture or Rangeland weeds - Cyperus rotundus            

4.   Non cropland weeds (Industrial weeds) - Xanthium strumarium,              Acanthospernum hospidum

5.   Aquatic weeds    - Eichhornia crassipes 

6.   Forest & woodland weeds - Lantana camera 

7.   Lawn and garden weeds    - Cyperus rotandus, Euphorbia spp.                 

 8.   Orchard and Plantation weeds – Cynodon dactylon, Cyperus rotandus 

9.   Weeds of Road side - Xanthium strumarium, Parthenium hysterophorus

 10.  Weeds of canal & irrigation channel - Cyperus spp., Cynodon  dactylon