Weeds

What is weed?
A Great Britain farmer Jethro Tull was the First person who have
defined weed in 1731 in his book “Horse Hoeing Husbandry”
“ A plant could be
undesirable at one place and
desirable at other place. E.g
Hariali, foxtail and goose
grass are valuable plant in
1. A weed is plant growing where
it is not desired.
2. A weed is a plant growing out of
its place
pasture but in
these are well
some weeds”
crop field
known trouble
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3. Any plant not sown in the field by
the farmer is out of place and is called
weed
“if farmer has sown a
sorghum crop in the
field then the plants/
vegetation other than
sorghum are4. Any plant or vegetation excluding
fungi interfering with the objectives or considered as weed”
requirement of people called weed
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Evolution of weed
Weeds are no strangers to man
They have been there ever since he started to
•
•
cultivate crops about 10,000 BC and
fromundoubtedly
the beginning
recognized as a problem
• Hence, it is considered that many weeds
principally originated from two important and
major arbitrarily defined groups-
By man’s conscious effort
By invasion of plants into man created habits


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Classification of weeds
Weeds are classified
•
•
•
•
•
•
•
•
Based
Based
Based
Based
Based
Based
Based
on
on
on
on
on
on
on
morphology
habitat
origin
association
life cycle
soil pH
nature of stem
Special classification
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Classification based on morphology/
cotyledon characters
Based on morphology, weeds are generally divided into following groups
• Grasses: Monocots, Stem is hollow except at nodes, Ligulate,
Alternate or opposite leaves, long, narrow leaves with parallel veins
Eg., Digitaria, Cyanodon
Sedges: Monocots, Stem is angular & solid, ligules are absent, Leaves
are arranged in whorls around the stem, have modifies rhizomes Eg.,
Cyperus, Scirpus
Broad leaved weeds: Mostly dicots having broad leaves with netted
venation Eg. Eclipta alba, Amaranthus spinosus, Portuloca oleracea
Algae: Chlorella, spirogyra, cladophora
Ferns: seedless vascular plants that produce spores Eg. Marsilea
crenata, Salvinia molesta
•
•
•
•
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Difference between grasses &sedges
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Grasses Sedges
1. Stem is hollow except at nodes 1. Stem Angular & solid
2. Ligulate 2. Does not posses ligules
3. Alternate or opposite leaves 3. Leaves in whorls around the
stem
Eg. Digitaria, Cynadon Eg. Cyperus, Scirpus

Digitaria
Cyperus
Salvinia molesta
Eclipta alba Marsilea crenataAGR 384
Chlorella

Classification based on habitat
TerrestrialDepending upon the place of their occurrence
they are classified into:
Aquatic weeds
Terrestrial weeds
Crop land weeds: weeds in field: Eg. Echinochloa in rice.
Non-crop land weeds: Weeds in waste lands Eg. Tribulus terrestris,
Xanthium strumarium.
Grass land weeds: Eg. Vernonia and Rumex spp.
Weeds of lawns & public parks Eg Lippia nodiflora and Eleusine indica.
Orchard or garden weeds Eg. Euphorbia geniculata, Imperata Cylindrica ,
Acalipha indica.
Weeds of plantation crops Eg. Euphatorium spp. Mikania micrantha
Road side weeds Eg. Euphorbia , Lantana camara , Hyptis and Prosopis juliflora
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Echinochloa colonum in rice.
Xanthium strumarium
Rumex spp
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Aquatic weeds:
i.
ii.
iii.
iv.
Submersed weeds: Eg. Utricularia stellaris, Ceratophyllum
demersum, Hydrilla Verticillata and Vallisneria spiralis
Emersed weeds: Eg. Nelumbium speciosum, Jussieua repens.
Marginal weeds: Eg. Typha, Polygonum, Alternanthera, Ipomea
Floating weeds: Eg. Pistia stratiotes, Salvinia
Nelumbium speciosum
Typha
Pistia stratiotesHydrilla Verticillata AGR 384

Classification based on origin
• Indigenous weeds(Apophytes): All the native weeds of the
country are coming under this group and most of the
weeds are indigenous. Eg. Acalypha indica, Abutilon
indicum, Sorghum halepense, Cyanodon dactylon and
Echinochloa colonum
Introduced or Exotic weeds or Alien: These are the weeds
introduced from other countries. These weeds are normally
troublesome and control becomes difficult. Eg. Parthenium
hysterophorus, Acanthospermum hispidum, Eichhornia
crassipes, Argemone mexicana, Lantana camara and Croton
bonplandianus
When man aids in its introduction such weeds are called as
antrophytes
•
•
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Parthenium hysterophorus
(From U.S.A)
Lantana camara
(From Sri-Lanka by birds)
Orobanche spp.
( Europe) etc
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Alien weeds vs Native weeds
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Alien/ Introduced weeds Native weeds
1. They are not native of India, 1. Seen within the geographical
They were introduced into India boundaries of origin.
2. They disseminate from their 2. Dissemination does not have
origin geographical boundaries
3. Introduced weeds can be 3. In case of native weeds, natural
effectively controlled by biological enemies are already existing
methods

Classification based on association
Based on association they are season bound weeds, crop bound
weeds and crop associated weeds.
• Season bound weeds: They are seen in that particular
season irrespective of crop.
These are either summer annuals or winter annuals. Sorghum
halepense is a summer perennial and Cirsium arvense is winter
perennial. Phalaris minor and Avena fatua are winter season
annuals.
Phalaris minor Avena fatuaAGR 384

Crop bound weeds: Weeds which usually dependent on the
host crop partially or fully for their nourishment i.e parasitism also
called as parasitic weeds.
Those parasites which attack roots are termed as root parasites
(Orobanche) and those which attack shoot of other plants are called as
stem parasites( Cuscuta).
Root parasites
a.
b.
Complete root parasite eg Orobanche (broom rape)in tobacco
Partial root parasite eg Striga spp (witch weed) on millets
Stem parasites
a. Complete stem parasite eg Cuscuta (dodder) in lucern & berseem
b. Partial stem parasite eg Loranthus in fruit crops
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• Crop associated weeds: such weeds grow along
with the crop due to their requirement of
microclimate and habitat and survive along the
crop in form of mimicry.Eg. Amaranthus viridis and
are associated with rice.
Echinochloa crusgalli
AmarAaGnRt3h84us viridis with
rice

Classification based on life cycle / ontogeny
Based on life span (ontogeny), weeds are classified as annual, biennial and
perennial weeds.
1.
a)
b)
Annuals: They are further classified into
Kharif season annuals Eg. Setaria glauca
Rabi season annuals Eg. Chenopodium album, Avena fatua, Phalaris
minor
Summer season annuals Eg. Argemone mexicana
Multi season annuals Eg. Echinochloa colonum, Eclipta alba
c)
d)
Chenopodium album
Setaria glauca AGR 384
Eclipta alba

2. Biennials: Eg. Daucus carota , Cirsium vulgare
Cirsium vulgareDaucus carota
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3. Perennials : They are further classified into
a)
b)
c)
Simple perennial: Ipomea carnea, Lantana camara
Bulbous perennial : Wild onion( Allium vineale)
Creeping perennial: Sorghum halepense
Sorghum halepenseWild onion
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Ipomea carnea

Classification based on nature of stem
Depending upon development of bark tissue on
their stems and branches weeds are classified into
woody, semi-woody and herbaceous weeds.
i. Woody weeds(brush weeds): Lantana camara,
Prosopis juliflora (mesquite), Zizyphus
rotundifolia
weeds.
(wild plum) are examples for brush
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Zizyphus rotundifolia (Jharber)
Prosopis juliflora (mesquite)
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ii. Semi-woody weeds: Croton sparsiflorus is
semi woody weed.
Herbaceous weeds: Weeds have green,
succulent stems are of most common
iii.
occurrence around us. Eg. Amaranthus viridis
and Chenopodium album.
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Amaranthus viridisCroton sparsiflorus
(SEMI -WOODY) Chenopodium album
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Herbaceous weeds

Classification based on soil pH
Based on pH of the soil the weeds can be
classified into three categories:
i. Acidophile
acetosella,
weeds habitat
Pteridium spp
acid soils eg. Rumex
Rumex acetosella Pteridium sppAGR 384

ii. Basophile weeds dominate in Saline &
alkaline soil Eg. Salsola spp dominate saline
soils where as Cressa erecta, Sporobolus
diander are dominant in alkaline soils.
Salsola spp Sporobolus diander
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iii. Neutrophile – Weeds of neutral soils Eg.
Acalypha indica
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Special classification
Poisonous weeds: Datura fastuosa, D.stramonium and D.
metel. The berries of Withania somnifera are also poisonous.
Parasitic weeds:The parasite weeds are either total or
•
•
partial which means for their growth. Eg. Orabanche, Cuscuta
Datura
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• Obligate weeds: Occur only on cultivated land or other wise
disturbed land and disappears when the land is not disturbed for 2-3
years and kept as fallow. Bind weed (Convolvulus arvensis)
Noxious weeds: These weeds are arbitrarily defined as being
undesirable, trouble some & difficult to control. They have immense
capacity of reproduction & high dispersal capacity. Argemone mexicana,
Cyperus rotundus, Parthenium, Cynadon dactylon, Lantana camara,
Saccharum spontaneum
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.
•
•
Obligate weed
Convolvulus arvensis
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• Faculative weeds or Apophytes- The weeds which
are wild community weeds and sometimes found in
cultivated area. E.g- Parthenium hysterophorus
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• Associated weeds ( Non- parasitic weeds)- The weeds which are
not dependent on other crop for its development and growth.
E.g- Cichorium intybus and Avena fatua
• Industrials Weeds
Weeds invading areas around buildings, highway, railway lines, fence
rows, electric and telephone pole bases etc are called industrial
weeds. Eg. Parthenium, Reshimkata, Katemath etc.
Cichorium intybus
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Reshimkata (Alteranthera triandra) Katemath (Amaranthus spinosus)
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Weed
process
management
• It is the of keeping or minimizing the
the
with
weed
level
population and their growth below
cropof economic injury to the
minimum environment pollution
Weeds can be managed by adopting• any suitable
method of weed control
more
and if needed by
combining
control.
two or methods of weed
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Importance of weed management
The total annual loss of agricultural produce
various due various parts in India is as below
1)
2)
3)
4)
Weeds: 45%
Insects: 30%
Diseases: 20%
Other pests (Rats, wild animals) 5%
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• A recent estimate shows that weeds cause annual loss of
Rs. 1980 crores to Indian Agricultural which is more than
combined losses caused by insects, pests and disease.
• Reduction in crop yields and production efficiency is
direct effect due to weeds. It varies from 30-35% (rice)
to 90.7% (onion).
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• Weeds compete with crop plants for plant for plant
nutrients, soil moisture, space and sunlight.
• Erosion of crop quality : Weeds cause food grains to shrivel
and decolouration of vegetables and fruits is also reported.
• Weeds as alternate hosts to crop pests and diseases: In rice
crop, Echinochloa and Panicum act as alternate host for
stem borer, whereas wild oats act as alternate host for stem
rust in wheat, oat, barley.
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Principles of weed management
I) Management- Optimizing losses below threshold level.
II) Preventive Measures: Inhibiting the entry
III) Control/ Curative Measures: Minimizing losses only
1)
2)
3)
4)
Mechanical methods
Cropping or cultural methods
Biological methods
Chemical methods
IV) Eradication- 100% removal
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Preventive methods of weed management
1) Use clean seed that is free from weed seeds for sowing purpose
2) Destroy the weeds before formation of flowers for avoiding seedling and
further spread of weeds
3) The cropped area, bunds irrigation channels, waste lands etc. should be
kept clean or free of weeds
4) Inspect nursery stock for the presence of weed seedlings, tubers,
rhizomes, etc.
5) Farm implements and machinery should be properly cleaned thoroughly
before moving it from one field to another
6) Avoid feeding screenings and other material containing weed seeds to the
farm animals.
7) Use vigilance (A farmer should inspect his farm periodically for strange
looking new weed).
8) Follow legal & quarantine measures.
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Mechanical Methods of Weed Control
1) Hand Pulling or Hand Weeding: Removal of weeds either manually or by
using tools like khurpi or sickle, when weeds grown upto some extent.
Tillage: Tillage removes weeds from the soil resulting in their death.2)
Tillage operation includes ploughing, discing, harrowing and leveling which is
through soil turnover and exposure of seeds to sunlight, which can be destroyed
effectively later.
3) Mulching: Principle is exclusion of sunlight from environment. Polythene
Sheets, natural materials like paddy husk, ground nut shells, saw dust etc. are
used as mulching material
Summer Fallow
Flooding : Flood kills weeds by excluding oxygen from their environment. Flooding is
a worldwide crop husbandry method of controlling weeds in rice fields.
Burning: It is cheapest method to eliminate the mature unwanted
vegetation in non-cropped areas and range lands.
4)
5)
6)
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Cultural Methods of Weed Control
1)
2)
Field preparation: The field has to be kept weed free.
Summer tillage: The practice of summer tillage or off-
season tillage is one of the effective cultural methods
to check the growth of perennial weed population in
crop cultivation.
Crop Rotation - The possibilities of a certain weed
species or group of species occurring is greater if the
same crop is grown year after year. Crop rotation is
effective in controlling of crop associated and crop
bound weeds such as Avena fatua in wheat and
Cuscuta in dodder.
3)
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4) Smothering- This crop germinates very quickly and
develop large canopy, capable of efficient photosynthesis
within short period. They possess both surface and deep
roots. Competitive crop smother the ground quickly than
non competitive crop. Eg; Cowpea, lucern, berseem,
millets., soybean, sun hemp, etc are good smother crops
Solarisation- In this method the soil temperature is
further increased by 5 to 100c by covering a pre-soaking
fallow field with transparent plastic sheet to kill
vegetative propagation
5)
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6)
7)
Proper Crop Stand and Narrow Spacing
Intercropping: Many short duration pulses viz., green gram
and soybean effectively smother weeds without causing
reduction in the yield of main crop.
Stale seedbed: A stale seedbed is one where initial one or
two flushes of weeds are destroyed before planting of a
crop.
8)
1. The weeds are allowed to germinate.
2. At this stage a shallow tillage or non- residual herbicide like
paraquat may be used to destroy the dense flush of young weed
seedlings.
This may be followed immediately by sowing. This technique
allows the crop to germinate in almost weed-free environment.
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Biological methods of Weed control
• The use of living organism (Bio-agents) such as insects, disease
organisms, herbivorous fish, snails and even competitive plants to
limit weed infestation is called biological control of weeds
The bio-agent which is specific to particular host weed can be used
for control of the weed
•
• Eg. Cyperus rotundus
“Bactra verutana”
can be controlled in crop fields with moth
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Chemical methods: Herbicides
Herbicides are chemicals capable of killing or inhibiting the growth
of plants.
Herbicides are primarly grouped into inorganic (Arsenic acid,
•
•
sulphuric acid, sodium chlorate) and organic herbicides (diesel
xylene type of aromatic oils).
oil,
• Eg. 2,4-D(s); Atrazine(s); Paraquat(ns)
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Eradication
It is complete removal of all live plant parts and
seeds of the weed from an area.
Because of its difficulty & high cost, eradication is
usually attempted only in smaller areas such as few
•
•
m2ha., a few thousand or less.
• Eradication is often used in high
green houses, ornamental plant
value areas such as
beds & containers.
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Weediness
In a simple words, it is a degree of
or
infestation.
It is a certain
weeds.
location, where is a abundance of
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CHARACTERISTICS
OF
WEEDS &
THEIR
IMPORTANCE

CHARACTERISTICS OF WEEDS
Nature has bestowed the following qualities on weeds:
1. Prolific seed production
• Produces larger number of seeds compare to crops
• In general, annual weeds are characterized by the
production of very large number of seeds.
• Seed production varies from 40 to 1,96,000 number of
seeds/plant.

• Most of the weed seeds are small in size and contribute
enormously to the seed reserves.
• Weed seeds germinate earlier and their seedlings grow
faster.

2. Vegetative reproduction
The vegetative reproduction is another way by which the
weeds were able to spread.
Some of the perennial weeds multiplied by various means
like:
 Tubers and nuts: nut grass
 Rhizomes and root stock: in grasses eg. Bermuda
grass & Johnson grass. In quack grass(Agropyron
repens) rhizomes are known as soboles.
 Bulbs: wild onion and wild garlic
 Roots: Canada thistle (Cirsium arvense)
 Stems: dodder (Cuscuta spp) and
 Offsets: Aquatic weeds (Pistia and Eichhornia)

3. Seed dormancy
• It is an efficient survival mechanism of weeds.
• It is defined as a state in which a viable seed fails to
germinate even under favorable conditions for plant
growth.
• Seeds of the most of the weeds exhibit one or other type
of dormancy like inherent or innate or natural dormancy or
induced or secondary dormancy or enforced dormancy by
wild mustard, black mustard and wild oats respectively.
• Avena fatua exhibit all the these kinds of dormancy

4. Longevity and viability of seeds
Weed seeds do not lose their viability for years even under
adverse conditions.
Lotus seed collected from the bottom of the Manchurian
lake bed have viability even after 1000 years.
Whereas, wild mustard and Chenopodium remain viable for
30 and 20 years, respectively.

5. Weed seed dispersal and germination
• Weed dispersal has no geographical boundaries.
• Common agents of weed dispersal are wind, water,
animals, birds, organic manures, agriculture
implements and human beings.

6. Wider adaptability
They have ability to thrive under adverse conditions due to
morphological and physiological conditions Eg. Trianthema
(carpet weed), Sorghum halepense and Saccharum
spontaneum.

7. Modified structure in order to
compete with crop plants
• They are provided with hooks, stiff hairs, thorns and
spines
• Eg. Argemone mexicana , Xanthium, Tribulus, and
Achyranthus spp.

• Other characteristic features like
• They have the capacity to germinate under varied
conditions, but very characteristically, season bound. The
peak period of germination always takes place in certain
seasons in regular succession year after year.
• Germination synchronization between weeds and crop
plants.
• They flower earlier and mature ahead of the crop they
infest.

• Rapid establishment and growth of weed seedlings
• Tolerance to shading effects by the crops at the time of
establishment
• Quick response to available soil moisture and nutrients.
• Most of the weeds possess C4 type of photosynthesis,
which is an added advantage during moisture stress.

• Relative immunity to post seeding soil disturbance
practices.
• They possess extensive root system, which go deeper as
well as of creeping type.

• Mimicry: Resembles the crop plants, morphological
characters are similar to the crop Plants. Wild oat in
wheat crop and Echinochloa colonum in rice.
Echinochloa colonum in rice.

Resistance to herbicides in use thus weeds are
called as “excellent competitors”

Importance of Weeds or Benefits or
Advantages Derived from Weeds
1) Weeds Add Organic Matter and Nutrients to the Soil:
• Many weeds have luxuriant leafy growth and when buried
in the soil as green manure add considerable amount of
organic matter and plant nutrients.
• Weeds add about 5 to 15 tonnes of green matter per
hectare depending upon weed species and their growth.
• Nutrient contents of some weeds are given below:
• Gokhru (Xanthium strumarium) - 3 to 3.5 % N
Bavachi (Psoralea corylifolia) - 3 to 3.5 % N
Leguminous weeds – 1.5 to 6 % N.

• Several species of weeds Tephorsia purpurea and Croton
sparsiflora in S. India used as green manures whereas,
Eichornia crassipes and Pistia stratiotes are used for
composting.

2) Weeds Check Wind, Water and Soil Erosion:
Weeds growing on desert lands, waste lands and sloppy
fields lower wind and water erosion and also help for
protection of the environment.
• Chenopodium album - used as mulch to reduce
evaporation losses
• Agropyron repens (quack grass) - used to control soil
erosion because of its prolific root system.

3) Some of the Weeds are used as Fodder for Animal:
• Some weeds have good palatable taste.
• Hariyali grass (Cynodon dactylon) and Cenchrus ciliaris,
Dichanthium annulatum, Eclipta alba weeds of grass land
serve as food for animals.

4) Some of the Weeds are used as Leafy
Eg.
Vegetables:
1.
2.
3.
4.
5.
Tandulaja (Amaranthus Polygamus)
Math (Amaranthus viridis)
Kunjru (Digera arvensis)
Ghol (Portulaca spp.)
Pathari (Lactuca runcinata)

5)
i)
ii)
iii)
iv)
v)
vi)
Some of the Weeds have Medicinal Value:
Gumma ( Leucas aspera) Used in snake bite.
Calotropis procera : Gastric troubles
Argemone mexicana : Skin disorders
Phyllanthus niruri : jaundice
Striga orobanchioides : control diabetes
Oil of Piwala dhotra(Argemone mexicana)
against skin disease.
– Useful
vii) Maka ( Eclipta erecta)- Against cough and as hair oil.

6) Some of the Weeds have Economic Importance:
• Kans (Saccharum spontaneum) – Used for thatching
purpose and breeding sugarcane varieties for including
hardiness.
• Nutgrass/ Nutsedge(Cyperus rotundus) - For making
essence sticks (agarbathis).
• Andropogan sp & Simbopogon spp. - For aromatic oils.

7) Reclamation of Alkali Soils:
The application of powder of the weed stayanashi piwala
dhotra ( Argemone Mexicana) @ 2.5 tonnes/ha is useful for
reclamation of alkali soils.

8) Some of the Weeds Serves as Ornamental and
Hedge Plants:
• Ghaneri ( Lantana camara) and Cactus – Used as
ornamental and hedge plants.
Ghol (Portulaca spp) – For beautiful flowers.

• 9) Certain Weeds have Nematicidal Properties
(Control of Nematodes)Crotalaria spp; Calotropis spp,
Parthenium etc. when incorporated in to the soil help for
control of nematodes.

10) NO2 and SO2 air pollution determined by wild mustard
and chick weed respectively.
11) Weeds can be used for Paper Pulp, Bio-gas and
Manufacture of Edible Proteins.
12) Some of the Weeds are used for Religious Purpose Eg.
Hariali, Aghada, Maka etc.

Weed Biology
• Weed biology is related to the study of weeds in relation
to their geographical distribution, habitat, growth and
population dynamics of weed species and communities.
• Knowledge of weed biology is of pivotal importance for
weed management and control in agriculture.
• The efficient propagation and different dissemination
potential are the sole reason for such spread.

Weed Ecology
• Ecology is the inter-relationship between organisms and
their environment.
• Weed ecology is study of inter-relationship between
weed and their environment.
• Weed ecology is thus concerned with growth
characteristics and adoptions that enable to survive with
changes in the environment.

Persistence of weeds
Weeds are highly persistent.
Persistence is a adaptive measure of a weed that
enables it to grow in any environment.
The persistence of an organism refers to repeatedly
invade an environment even when it is apparently
removed from the scene by man (or any other agent).
This should be differentiated from its hardiness, which
refers to its ability to withstand all kinds of natural stresses
at a given place.
Weeds are both persistent and hardy.
•
•
•
•
•

Persistence of weeds results
mechanisms such as
from their multifacet•
1.
2.
3.
4.
5.
6.
7.
8.
9.
Prolific seed production
Viable seed production
Dormancy
Vegetative propagation
Rapid dispersal
Inherent hardiness
Evasiveness
Self regeneration
Selective invasion
10 Weed succession

Propagation of weeds
Propagation is the process of creating new plants from
seeds, cuttings, bulbs or any other plant parts.
Broadly speaking there are 3 modes of propagation in
weeds (SEXUAL, ASEXUAL & VEGETATIVE
PROPAGATION) which give rise to different types of
propagules in different weed spp.

Modes of propagation of weeds
Propagation
Sexual Asexual Vegetative
o Propagation
through seeds
o Union of two
reproductive
units or the
gametes
without
union of
reproductive
cells
o Propagation througho
rhizomes root
stocks, runners,
tubers, bulbs,
bulbils, stems and
roots

a. Sexual Reproduction:
Propagation through seeds
Through sexual reproduction abundant and
produced.
•
• small seeds are
Annual and biennial weeds depend on seed production, as the
sole means of propagation (Seed production in such weeds is
prolific)
On the other hand perennial weeds are less dependent on this
mechanism for their survival weeds seed production facility is
limited like in eg. Cyperus and Cynodon spp which produce
only 40-170 seeds/plant but with exceptions which produce
thousands of seeds/year /plant by johnson grass (S.halepense)
and tiger grass (S. spontaneum) as annual weeds.
•
•

• Definition: This refers to fusion of two reproductive units or
the gametes by a) Conjugation b)Fertilization.
• Majority of our weeds are largely ‘monoecious’. A few like
Canada thistle (Cirsium arvense) and eel grass
(Vallisneria spirallis) are ‘dioecious’which bear male and
female flowers on different individuals

• Weed seeds are capable in retaining their viability for 2-25
years depending on weed species within the soil.
• Eg. Rumex spp showed 63-90% germination up to 2 to 7
years after these were buried upto 30 cm deep. While
Echinochloa, Poa and Chenopodium spp. germinated
even after 25 years.

b. Asexual reproduction
• This occurs without union of reproductive cells.
• Here each reproductive cell is simply cut off from the
parent plant and it grows into a new individual by
fission, budding, fragmentation or spore formation.
• Eg. weedy algae, horse tails (Equisetum sp) and ferns.

c. Vegetative reproduction
New plants are produced through vegetative parts of plant.
In this type of asexual reproduction a portion of mother plant either
stem or roots gets detached and grows into a separate individual
capable of colonizing new areas of land or the weeds may produce
some specific modified vegetative organs for this purpose both
above and under ground.
Vegetative propagation is primarily a feature of perennial weeds
and this has two advantages like purity of parental stock is
maintained and quick multiplication.
These modifications in the form of rhizomes, root stocks, runners,
tubers, bulbs, bulbils, stems and roots.
•
•
•
•

Rhizomes and root stock
• It is a horizontally growing underground modified shoot
bearing nodes, internodes, buds and scaly leaves.
• Cynodon dactylon uses rhizome under the ground, runners and
stolons over the ground.
• When rhizome tends to grow vertically downward, it s called a
rootstock, such as seen in Johonson grass (Sorghum
halepense).
• In quack grass (Agropyron repens) rhizomes are sometimes
called SOBOLES.

Sorghum halepense
Rootstock
Agropyron repens
SOBOLES

• The vegetative reproduction through rhizomes is feature
of perennial grasses, sedges, cattails and certain
broad leaf weeds including some ferns.

Runners
• Aerial shoots coming from axils of lower leaves are
called runners
• Eg. Bermuda grass, wood sorrel (Oxalis corniculata)
and
• The
and
pennywort (Centella asiatica)
runners trial on soils surface in different directions
strike roots from their terminal buds at short
distances. This is followed by appearance of new shoots
form their crown region. Daughter plants of such weeds
repeat the process and form big patches.

Runners
Stolons Suckers Offsets

These are different forms of runners:
• Stolons: When a runner, instead of trailing on the
soil surface, rises in the form of an arch before
hitting the soil, it is called a Stolon. (Eg. Cynodon
dactylon, Ranunculus repens)
• Suckers: trial little below the soil surface as in
hawkweed (Hieracium spp.).
• Offsets: Runners of floating weeds like water hyacinth
and water lettuce (Pistia lanceolata) are called Offsets.

Tubers
• Swollen ends of its wiry rhizomes and suckers are called
tubers.
• Eg. Nut sedge(Cyperus rotundus).A tuber possesses scaly
leaves, inconspicuous nodes and internodes, and minute buds
which give rise to new aerial shoots, rhizomes and roots.

Bulbs
• When crown region of a plant is compressed in the
shape of disc, it is called a bulb.
• Each bulb contains many fleshy leaves, axillary buds and
flowering buds at its apex.
Eg. Wild onion (Allium canadense) and wild garlic (Allium
spp.) propagate by bulbs.

Bulbils and Bulblets
• Bulbils, also called aerial bulblets, are modifications
of vegetative or flower buds.
• They are commonly found in woody sorrel (Oxalis
corniculata), wild onion and wild garlic, sprout leaf
(Bryophyllum pinnatum) and walking fern (Adiantum
candatum).
• Hydrilla(Hydrilla verticillata) produce aerial buds called
turions as additional means of vegetative
propagation.

Stems and Roots
• Fragments of stems and roots of many weeds can grow
into full plants.
• Detached stems pieces of dodder (Cuscuta arvensis) and
prickly pear (Opuntia spp.) and the creeping horizontal
roots of canada thistle, perennial sow thistle and field bind
weed for instance, are common means of propagation of
these weeds.

• Weeds propagated through vegetative propagation
mechanism are difficult to manage since their
propagates are located up to 100cm depth. Pluchea
lanceolate may hit several meters deep.

WEED DISSEMINATION:
of weeds
Dispersal
• Dispersal of mature seeds and live vegetative parts of
weeds is nature’s way of providing non-competitive sites
to new individuals.
• Had there been no way of natural dispersal of weeds, we
would not have had them today in such widely spread and
vigorous forms.
• In the absence of proper means of their dispersal, weeds
could not have moved from one country to another.
“Weeds are good travelers”

• An effective dispersal of weed seeds and fruits requires
two essentials
A successful dispersing agent
An effective adaptation to the new environment
i.
ii.
Common weed dispersal agents are
(a) Wind, (b) Water, (c) Animals and (d) Human

(a) Wind: Weed seeds and fruits that disseminate through
wind possess special organs to keep them afloat. Such
organs are
1. Pappus – It is modification of persistent calyx into hairs.
It is a parachute like structure
Eg. Asteraceae family weeds Eg. Tridax procumbens,
Dandelion (Taraxacum officinalis )

2. Comose –
Some weed seedsare coveredwith hairs,partially or fully Eg. Calotropissp.
Calotropis spp. (Comose) a &b

3. Feathery, persistent styles - Styles are persistent
and feathery Eg. Anemone spp.
4. Baloon - Modified papery calyx that encloses the fruits
loosely along with entrapped air. Eg. Physalis minima
5. Wings - One or more appendages that act as wings.
Eg. Acer macrophyllum

(b) Water: Aquatic weeds disperse largely through water.
They may drift either as whole plants, plant fragments or as
seeds with the water currents.
They posses lot of spongy, aerenchymatous tissue that
keep them afloat.
Terrestrial weed seeds also disperse through irrigation and
drainage water.
a. Hydrilla b. T.S. of stem showing aerenchymatous tissue

(c)Animals:
Birds and animals eat many weed fruits.
The ingested weed seeds are passed in viable form
which is dropped wherever the animal moves.
with animal excreta
0.2%
9.6%
8.7%
6.4%
in
in
in
in
chicks
calves
horses
sheep
Seed viability in their excreta
This mechanism of weed dispersal in called endozoochory.
Eg., Lantana seeds by birds, Loranthus seeds stick on beaks of birds.

• Farm animals carry weed seeds and fruits on their skin,
hair and hooves.
• This is aided by special appendages such as Hooks
(Xanthium strumarium), Stiff hairs (Cenchrus spp), Sharp
spines (Tribulus terrestris) and Scarious bracts
(Achyranthus aspera).
• Even ants carry a huge number of weed seeds. Donkeys
eat Prosophis julifera pods.

(d) Man:
• Man disperses numerous weed seeds and fruits with raw
agricultural produce.
• FARM PRODUCE: Weeds mature at the same time and height
along with crop, due to their similar size and shape as that of
crop seed man unknowingly harvest the weeds also, and aids
in dispersal of weed seeds. Such weeds are called “Satellite
weeds” Eg. Avena fatua, Phalaris minor in wheat seeds

Manure and silage:
• Viable weed seeds are present in the dung of farm animals,
which forms part of the FYM.
• FYM is an important source of dissemination of weed seeds
(Amaranthus,Trianthema, Cucumis sp.).
• C. arvensis retain its viability in FYM to the extent of 4% in the
1st month of composting and up to 1% two months later and nil
4thin .
• Silage and hay are also found to carry considerable viable
weed seeds.

Dispersal by machinery:
Machinery used for cultivation purposes like tractors can
easily carries weed seeds, rhizomes and stolons when
worked on infested fields and latter dropping them in
other fields to start new infestation.

Dispersal of vegetative propagules of weeds
• Careless cultivation of land is the important factor in the
dispersal of vegetative propagules of weeds.
• Cultivation detaches under ground organs such as
rhizomes, root stocks and tubers and drags them to
uninfected areas where they grow into new colonies.

Weeds

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