 Weeds are undesirable plants that have taken over areas that should be the area of desirable ones.  With the increasing international trade of crop it is become global problem of invasive weed due to contamination.  In the developing countries, weeding accounts for up to 60% of the total pre-harvest labor input  There are basically four approaches of weed management  Mechanical method,  Cultural method,  Biological method and  Chemical method  The Weed Science Society of America (WSSA) considered biological control techniques as a part of weed management strategy.  The population of weeds can be decreased through the biological control method, but weeds cannot be completely eliminated.  All the weed types can not be managed with this technique at a time.  Every weed has a unique characters for defeating crops, so it is important to understand its habits in order to understand how to get rid of weeds APPROACHES OF BIOLOGICAL WEED MANAGEMENT Two major types of biological weed control Classic (or inoculative) Approach  Commonly used technique and involves the introduction of natural enemies from their native range into an exotic range where their host plant has become a weed.  Considered to be an ecological response because the agent reduces the weed population below the socioeconomic or ecological threshold Non-Classical (or inundative)approach  Inundative strategy involves mass-production and application of a host-specific agent at high inoculum levels over a localized area infested with the target weed (Charudattan, 1991).  Weed control using this approach is relatively short-term and the biological control agent is not expected to be self sustaining. CHARACTERISTIC OF BIO-AGENT  For a bioherbicide to be successful, the pathogen must:  produce abundant and durable inoculum in culture,  be target specific,  Bioagent hardiness,  be capable of infecting and killing a significant portion of the weed population under a variety of environmental conditions.

1. Presenter:
SAMIR NEUPANE
Department of agronomy, IAAS, TU
PRINCIPLES AND PRACTICES OF
BIOLOGICAL WEED MANAGEMENT

2.  Introduction
 Approaches of biological weed management
 Characteristic of bio-agent
 Methods of biological weed control
 Types of bio-agents
 Merits and demerits
PRESENTATION OUTLINE

3. INTRODUCTION
Weeds are undesirable plants that have taken over areas that
should be the area of desirable ones.
With the increasing international trade of crop it is become
global problem of invasive weed due to contamination.
In the developing countries, weeding accounts for up to 60% of
the total pre-harvest labor input.
There are basically four approaches of weed management
Mechanical method,
Cultural method,
Biological method and
Chemical method

4. INTRODUCTION Cont...
The Weed Science Society of America (WSSA) considered biological
control techniques as a part of weed management strategy.
The population of weeds can be decreased through the
biological control method, but weeds cannot be completely
eliminated.
All the weed types can not be managed with this technique at
a time.
Every weed has a unique characters for defeating crops, so it
is important to understand its habits in order to understand
how to get rid of weeds.

5. APPROACHES OF BIOLOGICAL WEED MANAGEMENT
Two major types of biological weed control
Classic (or inoculative) Approach
Commonly used technique and involves the introduction of
natural enemies from their native range into an exotic
range where their host plant has become a weed.
Considered to be an ecological response because the
agent reduces the weed population below the
socioeconomic or ecological threshold

6. Non-Classical (or inundative)approach
Inundative strategy involves mass-production and application
of a host-specific agent at high inoculum levels over a localized
area infested with the target weed.
Weed control using this approach is relatively short-term and
the biological control agent is not expected to be self
sustaining.

7. CHARACTERISTIC OF BIO-AGENT
For a bioherbicide to be successful, the pathogen must:
produce abundant and durable inoculum in culture,
be target specific,
Bioagent hardiness,
be capable of infecting and killing a significant portion of the
weed population under a variety of environmental conditions.

8. METHODS OF BIOLOGICAL WEED CONTROL
Biological method is divided into two broad groups involving cropping
and competition and parasites, predators and pathogens
Cropping and Competition
Crop competition: One of the key factor that we consider while selecting and
developing improved crop is vigor and competitive ability
Crop rotation: Certain crops have strong association with some weeds than
with other, In rice field barnyard grass and jungle rice are frequently
found.
Plant Population:
Closer planting giving higher plant population which have a
competitive advantages over weeds.

9. Parasites, predators and pathogens:
Kinds of enemies:
•Microbial pathogens; virus, fungi, bacteria
•Parasitic higher plants
Control of weeds through bioherbicides:
Substances made from :
• Microbes like fungi, bacteria, viruses, or
protozoa
• Phytotoxic plant residues or extracts
E.g. A product is referred to as a
mycoherbicide when a fungus is the
active ingredient.
Fig. Di-Back Parkinsona
potentially eradicating Parkinsonia
aculeata.

10. TYPES OF BIO-AGENTS USED IN WEED MANAGEMENT
Carp fishes:
 (Chines grass carp) “Ctenopharyngo donidella” is promising
spp for aquatic weed control).
 Common carp (Cyprinus carpio) an omnivorous fish used
to control submerged aquatic weeds.
Insect:
 Insects are largely host specific
 Insects belong to Lepidoptera, Hemiptera,
Coleoptera, Diptera found effective.
 First successful example reported from
Hawai in 1902 Lantana camara controlled
by Moth, Crocidosema lantana.
Fig. Crocidosema lantana

11. Plant pathogen
 Many fungi attack specific weed species.
 Skeleton weed (Chondrilla juncia) controlled by rust causing fungi,
Puccinia chondrillana.
Snails
Marisa cornuarietis, the large
tropical fresh water snail,feed on
aquatic weeds;
 roots of water hyacinth, water
lettuce
 leaves of Salvinia.

12. Competitive plants
 Typha species can be controlled by Panicum
purpurascens or Brachiaria mutica (Para grass).
 Marigold has potential to displacing Parthenium
spp., Cassia sericea also suppressed

13. MERITS AND DEMERITS OF BIOLOGICAL WEED CONTROL
Merits
Environmentally friendly practices.
Comparably less expensive.
Safer to use and won't harm non
target plants.
It has a great deal of success in
weed control in uncultivated areas.
Besides this some fish, snails, and
other creatures make seafood out of
weedy vegetation.
Demerits
Multiplication is
somewhat expensive.
Control is sluggish.
Limited success of
control
There aren't many host
specific bio-agents on the
market right now.

14. grazing areas
inaccessible areas such as timbered, rocky and
steep locations
areas of low-priority for other forms of control
situations where biocontrol is the only option, for
example sensitive aquatic or environmental areas
situations where chemical control may not be
effective or it is too expensive .
BIOCONTROL IS PRACTICALAND EFFECTIVE FOR: