Weeds

Weed: 

Jethro Tull first coined the term weed in1931 in the book ' Horse Hoeing Husbandry'.

Define : Weeds are the plants where they are not wanted.

Plants out of place 

• Classification of Weeds: 

Weeds are  classified

1) Based on morphology

2) Based on life cycle 

Based on habitat

Based on origin

Based on association

Based on nature of stem

Based on soil types

Special classification

Classification based on morphology / cotyledon characters:

During 1940 2,4 -D was discovered and it was a selective translocated Herbicide 

Weeds are generally divided into

1) Grasses

2) Sedges

3) Broad leaved weeds

• Classification based on habitat:

Depending on place of their occurrence the are classified into

 1) Terrestrial weeds

2) Aquatic weeds

Terrestrial weeds are again classified into :

1) Crop land weeds

Weeds in field

E.g. Echinocloa in rice 

2) Non crop land weeds:

Weeds in a waste land 

Xanthium strumarium 

3) Grass  land weeds

Vernonia

4)Eleucine indica

5) Orchard or garden weeds

Euphoria geniculata

6)Weeds of plantation crops:

Euphoria spp.

7) Parasitic weeds: 

E g. Loranthus , Striga spp

8) Road side weeds:

Lantana camera

9) Aquatic weeds:

They are classified as

1) Sub merged weeds:

 Hydrilla verticillata

2) Emerged weeds

Typha spp

3) Floating Weeds: 

Eichhornia crassipes

• Classification Based on Origin

✓ 

Indigenous Weeds :

   All the native weeds of the country 

are coming under this group

E. g

1)Sorghum helpense

2) Cyanodon dactylon

3) Echinocloa colonum

✓Introduced or Exotic weeds or Alien:

These are the weeds introduced from the other countries .

These weeds are normally troublesome and control becomes difficult.

1) Parthenium hysterosporous

2) Argemone mexicana

3)Anthospermum hispidium

4) Lantana camera

When man aids in its introduction such weeds ars called as Anthrophytes.

✓ Classification based on association :

When two plants are living together are called as Association.

Based on association they are

1) Season bound weeds

2)Crop bound weed

3) Crop Associated weeds

✓Season bound weeds:

They are seen in that particular season irrespective of crop

Sorghum helpense is a summer perennial and 

Phalaris minor and Avena fatua are winter season annuals 

✓Crop bound weeds

Weeds which usually parasite the host crop partially or fully for their nourishment i.e. Parasitism also called as parasitic weeds

Those parasite which attack roots are termed as root parasite 

And those which attack the shoots of the other plants are called as stem parasites 

Root parasites:

a) Complete root parasite:

Orobanche (Broom rape )in tobacco

b)Partial root parasite

e.g. Striga spp.(Witch weed) on millets

2) Stem parasite:

a) Complete stem parasite:

e.g. Cuscuta( Dodder) in lucern and Berseem

b)Partial Stem parasite

Loranthus in fruit crops

3) Crop Associated Weeds:

Ready to contamination with the crops

Mimicry:

If weeds look exactly like crops morphologically and complete their life cycle

E.g.

1) Echinochloa colonum (Jungle rice)mimic the rice crop

2) Avena fatua(Wild oat) and Phalaris minor( Canary Grass) both mimic the wheat

Loranthus in tea gardens.

✓Based on life cycle:

Based on life cycle (Ontogeny)

Weeds are classified as 

Annuals, biennial and perennial weeds,

Annuals :    Complete it's life cycle within one year or one season and propagate by seeds

Annuals they are again classified into

a) Kharif season Annual 

Digera arvensis ( Digera)

b) Rabi season annual

1)Chenopodium album ( Lamb's quarters)

Avena fatua(Wild Oat)

Phalaris minor

c) Summer season annual

1) Setaria glauca ( Yellow foxtail)

d) Multi season annual 

1) Echinochloa colonum

2) Phyllanthus niruri

Amranthus viridis is even though is is summer/kharif annual but it is seen throughout the year when Irrigation is available

Ephemerals:

Are short lived annuals which complete their life cycle within 2-4 weeks

e.g. Phyllanthus niruri

2) Biennial

Complete it's life cycle within two years or two seasons. 1st year Vegetative growth - Rosette condition

Second year produce inflorescence called as bolting

e.g. Chicorium intybus

3) Perennial :

 Grow  more than two years

Difficult perennial weeds are also know as pernicious weeds.

E.g. Cyanadon dactylon (Bermuda grass)

Agropyron repens (Quack grass)

Again they are 

1) Simple perennial

2) Bulbous perennial

3)Creeping perennial 

✓Special Classification

They are 

1) Poisonous weeds

The poisonous weeds cause ailment on livestock resulting in dealth and cause great loss.

Datura fastuosa 

Datura stramonium 

Datura metel 

Are poisonous to animals and human beings

2) Parasitic weeds

3) Aquatic weeds

Unwanted plants which grow in water 

and complete at least part of their life cycle in water is called as aquatic weeds.

1) Submerged weeds

These weed are mostly vascular plants that produce all or most of thiir vegetative growth beneath the water surface .

e.g. Hydrilla verticillata 

2) Emersed weed:

These plants are rooted in the bottom mud with aerial stems and leaves at or above the water surface 

Typha spp. e.g. Nelumbium speciosum

3) Marginal Weeds: 

Weeds that can grow in moist shoreline areas with a depth of 60 to 90 cm water 

4) Floating weeds:

These weeds have  leaves that float on the water surface either singly or cluster.

e.g. 

Eichhornia crassipes (Jalkumbhi)

Facultative weeds: also called as Apophytes. Weeds that grow primarily in wild community migrated in crop fields

e.g. Opuntia dilleni

Obligate weeds: Occur only on Cultivated land

e g. Convovulus arvensis

Noxious weeds: Defined as undesirable, troublesome and difficult to control . these are also called as special problem weeds.

Cyprus rotundus

Cyandon dactylon

Striga spp

Parthenium hysteroporous 

Lantana camera

Saccharum spontaneum

Eichhornia crassipes

Objectionable weed:

It is a noxious weed whose seed is difficult to separate from the crop seed after contamination is called objectionable weed.

✍️Agricos Vaishnavi Nimkar

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