10. basic of inegrated agents by Allah Dad Khan

2. BASICS OF INTEGRATED WEED
CONTROL

3. The definition of weeds is predicated on
human perception , desire and needs.
1. A weed is a plant which interferes with
human activity or welfare.
2. It is also defined as plant growing in a place
where it is not desired at a particular point in
time.

4.  Weeds are classified as native or introduced
according to their origin. Plant origin may help
determine weed management strategies and the
difficulty of control.
 Native weeds have historic origins in the area and
were not brought here by human activity. Natural
enemies, competition from other plants, and
environmental conditions hold many native weed
populations in check.
 Sometimes these plants may be troublesome, but
native plants rarely become problem weeds.

5. Introduced plants came from other parts of the
a. country or world by accident or
unintentionally.
b. The Pacific Northwest often lacks the
weed’snatural predators or limiting factors
such as climate to hold them in check.
c. Lack of natural control allows the weeds to
flourish andspread. Most problem weeds are
introduced plants.

6. Escaped plants were intentionally introduced by
humans as crops, forage, or ornamentals.
1) They subsequently have spread beyond their
intended areas. Again, the natural mechanisms
that suppress these weeds were not imported
with them or are not present in the new
environment.
2) Dalmatian toadflax, Scotch broom,and kochia
are examples of escaped ornamental plants.

7. Weeds spread when outside agents move or carry
seeds or growing plant parts (roots, rhizomes)
into new territory. Some invading weed species
have evolved special seed shapes or structures
to aid their movement by wind, water, or
animals. Also, many plants have vegetative
parts that resprout new roots or shoots. When
carried into new areas, these plant fragments
may grow and start new infestations

8. Wind carries many seeds to new areas. Weeds
such as dandelions have a parachutelike
attachment that carries the seed in the wind
For other weeds, the entire plant moves or
tumbles with the wind, dropping seeds as it
rolls; tumble mustard and Russian thistle are
common examples.

9. Water from rain or irrigation and the subsequent
surface runoff transports many seeds. Some
seeds have an oily coating or an air bladder to
aid flotation. Rivers, streams, and irrigation
canals move large numbers of seeds.

10. Mammals, birds, and humans carry seeds on their
bodies, dropping them into new areas. Plants
have seed shapes (burs, hooks, barbs) that cling
to feathers, hair, and clothing. Some seeds are
ingested and excreted by wild or domestic
animals. The seeds often survive and
subsequently germinate after they have passed
through an animal’s digestive tract.

11. Practices that Increases Biodiversity:
• Intercropping
• Crop Rotation
• Cover cropping
and Strip cropping
Decrease in Biodiversity can be caused by:
• Monocropping
• Tillage
and Herbicides use
Biodiversity leads to more stability for the ecosystem as a whole.

12. Harmful to humans, animal and crops Wild and Rank growth
in an environment Exhibits persistency
 High reproductive capacity: large number of seeds, possess
diffeent types of propagules e.g. Seeds, tubers , rhizomes,
1. Seed Dormancy : could be innate, induced or enforced.
2. Usually present in large populations..
 Could be regarded as being useless, unwanted and
undesirable
 They exhibit spontaneous appearance without being
planted
 Some exhibit mimicry. (seed, vegetative and biochemical )
• Many weeds are aggressive and have rapid seedling growth

13. • Reduction in quality of pasture land; it reduces the
carrying capacity of grazing lands and pastures
through their physical presence and weediness
• Reduction in quality of animal products;it affects the
palatability of pastures, hay, silage etc. protein
content in alfalfa wild garlic (Alliums spp) when
eaten by cattle spoils the meat and the milk.
• Serve as alternate hosts for many plant diseases and
animal pests e.g. insects, rodents, birds. Cyperus
rotundus serve as alternate to nematodes and
athropods
• Impose limitation to the farm size of a farmer
• Can serve as sources of fire hazards

14. 1. Reduce erosion problem through the production of
protective cover
2. Help in nutrient recycling through decay of vegetative
part.
3. Food/vegetables for humans e.g. leaves of Talinum
triangulare, and tubers of Colocasia esculentus .
4. Serve as hosts and nectar for beneficial insects
5. Beautification of the landscape e.g. Cynodon dactylon

15. Feed for livestock and wildlife and aquatic organisms in form of hay, silage
and forage / pasture, fruit seeds and branches and whole plant.
1. source of pesticides e.g. Chrysanthemum cinerariifolium
2. Source of genetic material for useful traits in crop improvement.
3. Medicinal use e.g neem ( Azadirachta indica), Ageratum conyzoides
4. Some serve as trap crop for parasitic weeds.
5. Habitat for wildlife and plant species hence biodiversity conservation.
6. Major role in carbon recycling through carbon sequestration. Field of
exposed soil always suffers a net loss in organic matter and releases carbon
dioxide, while a field covered with crops and/or weeds takes up carbon
dioxide. This concept of carbon sequestration is an added advantage of
sustainable and organic farming.

16. Weeds can serve a purpose; here are benefits weeds offer:
1. Soil fertility and water holding capacity. Perennial weeds such as thistles, nightshades,
and pigweeds are deep rooted and penetrate the subsoil. Root penetration breaks up the
soil and allows water and nutrients to move up and down through the soil. Moisture
seeps down and phosphorous and potassium are drawn to the surface for use by other
plants.
2. Habitat for beneficial insects. Weeds in the sunflower (Asteraceae), parsley (Apiaceae),
and mustard (Cruciferae) families are nectar sources for beneficial insects. Most weed
flowers are shallow throated making their pollen and nectar easily available to beneficial
insects.
3. Trap crops. A border or row of weeds along a garden will attract pest insects that
otherwise might concentrate in the garden and harm crops. You can encourage weeds
that attract pest insects. Keep weeds lush and irrigated to attract insects, but cut back the
top of weeds before they flower and set seed. Monitor weedy trap crops for insect eggs
and pest insect larvae; handpick or spray pest insects in trap crops before they move into
the garden.
4. Soil protection. Low growing weeds that compete poorly with vegetables can protect
the soil from drying out. As long as weeds are not competing with crops for moisture
and nutrients, they can hold the soil in place and keep the sun

17. 1. Most weeds occur in the division Anthophyta
(Angiosperms, which are further divided into the classes
dicotyledones (dicots) and monocotyledons (monocots)).
2. There are approximately 250000 species of plants in the
world. However, less than 250 plant species, about 10%,
are troublesome enough to be called universally
throughout the world.
3. On the basis of the habitat, weeds are divided into
terrestrial and aquatic categories and on the basis of
duration of life, they are divided into annual, biennial and
perennial.
4. Annuals complete their life cycle in a year or in a single
growing season. They mostly propagate through seeds.
Normally, they germinate with the crop and complete their
life cycle before or along with the crop. Based on the
season they are encountered, weeds may be called as
summer and winter annuals. Some examples are:

18. 1. Summer Annuals: Echinochloa colona, E. crus-galli,
Amaranthus viridis, Trainthema portulacastrum, Eclipta alba,
Digitaria sanguinalis, Panicum repens.
2. Winter Annuals: Phalaris minor, Avena ludoviciana, Poa annua,
Chenopodium album, Melilotus indica, Lathyrus aphaca,
Anagallis arvensis.
Biennials live longer than 1 year but less than 2 years. During
the first growth phase, they develop vegetatively from a
seedling into a rosette. After a cold period, the growth resumes
into reproductive phase. Biennials are large plants when mature,
and have thick fleshy roots. Relatively few weed species are
biennials, e.g. Cichorium inttybus, Raphanus raphanistrum.
Perennials live longer than 2 years and may reproduce several
times before dying. They are propagated through seeds and
vegetative reproductive organs like rhizomes, suckers, bulbs and
tubers, e.g. Cynodon dactylon, Saccharum sp

19.  Aquatic weeds:
They have been categorized further as floating, emerged and submerged.
Floating weeds:
These rests upon the water surface. Their roots hang freely into the water
or sometimes attach to the bottom of shallow ponds or streams, e.g. water
hyacinth, Pistia, Salvinia, etc.
 Emergent weeds:
Typical plants of marshlands and are often found along the shorelines of
ponds and canals. These plants stand erect and are always rooted into
very moist soil, e.g. Typha, Scirpus, etc.
 Submerged weeds:
Grow completely under water, although a few stems and leaves may exist
on the water surface, e.g. Hydrilla, Chara, Potamogeton, etc.
 Parasitic weeds:
These weeds parasitize on specific host plants and deprive them of water,
nutrients and assimilates. They may be root parasites (Orobanche, Striga)
or shoot parasites (Cuscuta). They are either partial parasites (Striga) or
total parasites (Orobanche), depending on the degree of parasitism.

20. Ecology is the study of the relationship of plants and
animals to their physical and biological
environment. Physical environment like light, heat
solar radiation, moisture, wind, oxygen, carbon
dioxide, nutrient soil, water and atmosphere.
Biological environment includes organism of the
same kind as well as other plants and animals
Weed ecology is generally about the growth
characteristics (ii) adaptation (iii) survival
mechanism of weed that enables them to exploit
environmental resources and successfully colonize
new habitat often at the expense of other
neighboring plants

21.  A habitat is a dwelling place or a kind of
environment occupied by the individuals of a
species. Habitat may imply places like rubbish
dump, farm land or other sites occupied by
weeds.

22. • Niche: it is the condition in a location under
which a species can live successfully. Within the
habitat, organisms occupy different niches.
• A niche is the functional role of a species in a
community—that is, its occupation, or how it
earns its living. For example, the scarlet tanager
lives in a deciduous forest habitat. Its niche, in
part, is gleaning insects from the canopy foliage.
The more a community is stratified, the more
finely the habitat is divided into additional
niches.

23. • Ecosystem is the energy driven complex
system in which the living organisms interact
with themselves and the environment.
• Weed- crop ecosystem involves weed-crop
interaction as well as the nature and the
function of that ecosystem. This will assist in
understanding the impact of crop production
and husbandry on the shifts in weed flora, for
instance the persistent of weed in given
weed- crop ecosystem.

24. • Weed persistence is a measure of the adaptive potential of weeds that enables them to
survive in disturbed environment such as i. Crop land ii. Recreational site iii. Irrigation
canal and iv. Pastures
• The adaptive features or survival mechanisms of annual weeds include: i. Production of
large quantities of seeds ii. Seed dormancy and iii. Periodicity of seed germination and
short life span.
• The adaptive features of perennial weeds include: i. Deep rooting ii. Dormancy iii.
characteristics of buds on rhizome iv. Other modified stems and v. Fragmentation of
parts
Types of peennating and reproductive vegetative structures in perennial weeds:
1) 1. Rhizome – underground, horizontal stem (quackgrass, swamp smartweed)
2) 2. Stolon – aboveground, horizontal stem (bermudagrass)
3) 3. Tuber – swollen stem tissue (yellow nutsedge)
4) 4. Bulb – stem with shortened internodes and fleshy modified leaves (wild garlic)
5) 5. offset
6) 6. bulbils
7) 7. corm
8) 8. runners
9) 9. suckers

25. Storage organs may act as 'perennating organs‘
These are used by plants to survive adverse
periods in the plant's life-cycle (e.g. caused by
cold, excessive heat, lack of light or drought).
During these periods, parts of the plant die
and then when conditions become favourable
again, re-growth occurs from buds in the
perennating organs. For example geophytes
growing in woodland under deciduous trees
(e.g. bluebells, trilliums) die back to
underground storage organs during summer
when tree leaf cover restricts light and water is
less available.

26.  Crop mimicry is an example of the extent to
which weeds have adapted themselves to
survive in that frequently disturbed site.
 Crop mimicry is defined as the phenomenon
whereby weeds develop morphological and or
biochemical close resemblance to some phases
in the life history of a crop as to be mistaken
for the crop and thus evade eradication.

27. 1. Vegetative mimicry:A situation where close similarity in appearance
occurs between weeds and crops at seedling and vegetative
stages.e.g. wild rice (Oryza longistaminata) in cultivated rice ; wild
sorghum (Sorghum halepense) in cultivated sorghum, wild
sugarcane (Saccharum spontaneum) in sugarcane.
2. Seed mimicry:This is a situation whereby the similarities between
weeds and crops is observed in seed, weight, size and appearance.
e.g. similarity in seed size between seeds of upland rice and those
of itch grass (Rottboellia cochinchinensis).
3. Biochemical mimicry:This is a situation in which a weed develops
resistance to a herbicide that has been used previously for
selective control in a given crop.

28. Weed persistence can be affected by:
1. Climate e.g light, temperature, water, and
wind
2. Soil (edaphic)
3. Biotic factors e.g. plants and animals

29. When plants grow close to each other, they interact in
various in ways.
1. Interference: It is the detrimental effects of one
species on another resulting from their interactions
with each other. When plants are far apart they
have no effect on each other. Interaction generally
involves competition and amensalism.
2. Commensalism: This is the relationship between
unrelated organism (different species) in which
one derives food or benefit from the association
while the other remains unaffected.

30. 3.Competition (allelospoly): It is the relationship
between two plants (weed/crop, crop/crop,
weed/weed) in which the supply of a growth
factor falls below their combined demand for
normal growth and development. The growth
factor competed for include water, nutrients,
light, space and air/gasses (oxygen, carbon
dioxide).

31. 1. Above-ground (Aerial) competition : Takes
place in the leaves and the growth factors
involve are light and carbon dioxide.
2. Below-ground(Subterranean) competition:
Takes place mainly in the roots while the
growth factors involve are water, nutrients and
oxygen.
3. The perceived consequence of competition
with crop is reduction in the economic yield of
affected crop plants.

32.  Intraspecific competition: competition for growth
factors among individuals of a plant species
 Interspecific competition: competition for growth
factors between two different plant species i.e
crop/weed, weed/weed,or crop/crop

33. Critical Period of Weed
competition/interference:
This is the minimum period of time during which the
crop must be free of weeds in order to prevent loss in
yield .
it represents the overlap of two separate components
(a) the length of time weeds can remain in a crop before
interference begins
(b) the length of time that weed emergence must be
prevented so that subsequent weed growth does not
reduce crop yield.

34. Competitiveness of weed species
1) Weed density and weight
2) Onset and duration of weed-crop association
3) Growth factors
4) Type of crop and seeding rate
5) Spatial arrangement of crops
6) Plant architecture
7) Growth factors availability
8) Cropping patterns
9) Crop type (C3 or C4 plants)
10) Crop variety( tolerance, resistance, aggressiveness)

35. Environmental factors
1. Climatic factors e.g. rainfall, temperature,
wind, light etc
2. Tillage
3. Ground water management
4. Soil (Edaphic)

36. • Amensalism (Allelopathy)
• Allelopathy is the production of chemical(s) or
exudates by living and decaying plant species which
interfere with the germination, growth or development
of another plant species or microorganism sharing the
same habitat.
• There are two types of allelopathy:(True and
Functional )
• True allelopathy involves the release into the
environment compounds that are toxic in the form they
are produced. Functional allelpathy involves the release
into the environment substances that are toxic as a
result of transformation by microorganism.

37. Allelochemical complex commonly encountered in plants include:
coumaric acid, terpenoids, - syringic acid, butyric acid, flavonoids,
phenolic compounds.
Examples of allelopathic plants:
1. Black walnut (Juglans nigra)
2. Gmelina arborea
3. Soghum bicolor
4. Casuarina
5. Lantana camara
6. Imperata cylindrica is allelopathic on tomato, cucumber, maize
rice, glnut, olera, cowpea, pepper.
7. Cyperus esculentus– is allelopathic on rice, maize
8. C. rotundus – is allelopathic on barley.

38. ParasitismIt is a relationship between organisms in which one lives as a
parasite in or on another organism.
Parasitic weeds are plants that grow on living tissues of other plants and
derive part or all of their food, water and mineral needs from the plant they
grow on (host plants)
1. Hemi parasite (Semi parasite) a plant which is only partially parasitic,
possessing its own chlorophyll (green colour) and photosynthetic ability
(may be facultative or obligate). E.g Striga hermonthica
2. Holo parasite – a plant which is totally parasitic, lacking chlorophyll
thus unable to synthesize organic carbon. E.g Orobanche spp
3. Obligate parasite – a plant which cannot establish and develop without a
host
4. Facultative parasite – a plant which can grow independently but which
normally behaves as a parasite to obtain some of its nutrition.

39.  Predation: It is the capture and consumption of organisms by
other organisms to sustain life.
1. Mutualism: it is an advantageous relationship between two
organismsof different species that benefits both of them. It is
obligatory and the partners are mutually dependent. Both partners
are stimulated when the interaction is on. Example is the case
between fungus and algae. The fungus protects the algae while the
algae provide carbohydrate for the fungus.
2. Neutralism: This is the situation where plant exert no influence on
one another.
3. Protocooperation: This is a condition whereby two plants interact
and affect each other reciprocally. Both organisms are stimulated
by the association but unaffected by its absence.