biological weed control ,what is bio-control of weed ,how biological control of weed works ,advantage of biological weed control ,methods and agents of biological weed control

1. “BIOLOGICAL WEED
CONTROL”

3. Biological control of weeds is the deliberate use of
natural enemies to reduce the density of a particular weed to
a tolerable level The objective of biological weed control is
not eradication but simply the reduction of the weed
population to an economically low level In fact for biological
control to be continuously successful, small numbers of the
weed host must always be present to assured the survival of
the natural enemy.
Introduction

4. What is biological control?
 Biological control uses one living organism to control another. The aim
of a weed biological control program is to introduce natural
enemies(insects, mites or diseases) that will reduce the density of the
weed to a level that is manageable and will reduce its impacts.
The origins of biological weed control
 In ancient times, the Chinese discovered that increasing ant populations
in atheir citrus groves helped decrease destructive populations of large
boring beetles and caterpillars. That use of a natural enemy to control a
pest marked the birth of biological control.

5.  Roots provide plants with water and nutrients. Some biological control
agents attach to roots and thereby stunt plant growth. Some bacteria live
on root surfaces and release toxins that stunt root growth. Many fungi
infect roots and disrupt the water transport system, which reduces leaf
growth.
 Beneficial insects and nematodes feed directly on the weed roots causing
injury which allows bacteria and fungi to penetrate. Plant leaves capture
energy from the sun and store it as sugar. Insects that feed on leaves
reduce the leaf surface available for energy capture. Fungi and bacteria
that infect leaves reduce the ability of the leaf to make sugars.
How does it work ?

6.  In either case, there is less energy available for weed growth. Whether
through damage on roots or leaves, severe infestations of biological
control agents can actually kill weeds, reducing their adverse effects on
desirable plants.
 Some bacteria and fungi applied as biological control agents do not
survive from year to year. These organisms must be applied on an
annual basis. This technique is called the "bio herbicide" strategy.
 With this tactic, biological agents are used a in manner similar to
chemical herbicides. Weeds introduced from foreign countries often
require a different strategy. Insect agents often require a number of
years to become fully effective.

7.  Bioagent like insects, pathogen etc. and other animals are used to
control weeds.
 Insect and pathogens infest weeds and they either reduce growth or
kill weeds.
 Biological control method can reduce weeds but it is not possible to
eradicate weeds.
Biological Control Agents
Insects have been most frequently used as biological control
agents of weeds and this will likely continue. The reasons are that there
have been major successes using phytophagous insects and almost all of
the scientists working in biocontrol of weeds are entomologists.
However, recent research has demonstrated the potential of other
organisms, including plant pathogens, nematodes, and fish.
BIOLOGICAL METHODS OF WEED CONTROL

8. How are biological control agents selected?
 Biological control agents are selected very carefully. A study is
carried out overseas to identify all the organisms found
attacking a weed.
 Some of these species will be chosen for further testing. Any
agent imported for biological control of a weed must be host
specific, that is, it will only attack the target plant.
 Stringent testing is carried out on close relatives of the weed
including native, ornamental and crop plants.

9. Procedures in Classical Biological Control
The first step in a biological weed control program is to determine
the suitability of the weed for this approach. Not all weeds are suitable and
those with the following characteristics are generally least suited for
biological control:
 Weed species which are valued in other situations are not good
candidates for this approach. As the biocontrol agent cannot be limited
in area, like chemical or mechanical treatments, 'weeds' that are of
values in other situations are not suitable targets for bio control.
 Weeds that are closely related to economic crops are not good
candidates for this method. The closer the relationship the less
possibility there is that a biotic agent could distinguish between the
weed and the crop.

10. 3. Native weed species are not generally amenable to this approach.
However, the native range of an introduced alien weed provides a source
from which a parasite can be introduced.
4. Weeds of cropland under intensive cultivation are generally not suited
to this approach. Since the biological control agent is specific to only
one weed species, However, biocontrol is particularity suited to
rangeland situations where a single, dominate weed species is
troublesome.
5. Minor weed problems are not generally suited to this approach. The
target weed should infest large areas.
6. If eradication of the weed is desired (e.g., poisonous weeds) the
method is generally not applicable.

11. Methods Used in Bio control of Weeds
The classical approach to biological control of weeds
involves the introduction of host-specific natural enemies of
allien weeds. Recently the approaches utilized in bio control
programs have been expanded to include two other methods:
1) Augmentation of natural enemy populations
2) Application of "biological herbicides.

12. 1. Augmentation of natural enemy populations
Conventional approach
As discussed above, biological control of
weeds has conventionally been applied against alien weeds
by introducing one or more of their natural enemies.
Augmentation includes the periodic release and/or
distribution of natural enemies.

13. 2.Biological Herbicides
A new approach to biocontrol of weeds has recently been
pioneered in Arkansas with the application of a spore suspension of
an endemic fungus. when the fungus was applied early in the
seedling stage, it destroyed the weed.
An attractive feature of this method is that it does not involve the
introduction of any new organism into our environment but merely
the use of host-specific pathogens at a time when they are most
effective. This method may also prove to be valuable for integrated
weed control systems. For example, most weeds are controlled in
corn with standard herbicide application, but a few weeds such as
quackgrass (Agropyron repens) and yellow nutsedge(Cyperus
esculentus) are more difficult to control.

14. Bio-agent Weeds
Insect
Two beetles:
leaf beetle (Octotoma scabripennis)
Leaf-mining chrysomelids (Uroplata giraldi)
Lantana camara
Scale insect
Dactylopius tomentosus.
Prickly-pear weed
Flea beetle
Agasicles hygrophyla
Alligator weed
Alternanthera philoxeroides
Fish
Common carp (Cyprimus carpio)
Chinese carp
Aquatic weeds
Mammals
Manetee or sea-cow Water hyacinth
Fungi
Rhizoctinia blight. Hyacinth
Snails
Marisa sp. and other fresh water snails Submerged weeds like coontail and algae
Mites
Tetranychus sp Prickly pear
Plants
Cowpea as intercrop in sorghum
Effectively reduces the growth of weeds in
sorghum

15. 1) Specific to one plant species
2) Has negative impact on host plant individuals & its population
3) Is prolific
4) Thrives and becomes widespread in all habitats & climate that the pest
weed occupies
5) Is good colonizer
6) Less overall expense compared to other control tactics
7) Does not require a high level of technology
8) Less disruptive ecologically & so natural biodiversity is maintained
Considerations for species for introduction pest to
control weeds

16. Plant Pathogens as Biocontrol Agents of Weeds
Plant pathogens offer two advantages over insects as biocontrol
agents of weeds:
 They are often more host specific, and
 They can be applied with conventional spray equipment at
time when the weed is at its most susceptible stage.
Aquatic Weed Control
 Biocontrol of water weeds is the to use of bio agent like fish, fungi
and other for the aquatic weed control.
 e.g. Common carp, Rhizoctinia blight, sea-cow.

17. Advantages
 Biological control can be cost effective in the long run.
 A high degree of specificity of target weed.
 No effect on non-target and beneficial plants or man.
 Absence of residue build-up in the environment.
 Effectiveness for managing herbicide-resistant (HR) weed populations.
Limitations
 The weed must be highly specialized.
 It must, in the new environment in which it has established itself.
 A lot of planning an money goes into developing a successful system.
 It’s a slow process. It likes a lot of time and patience for the biological
agents to work their magic on pest population.

18. Reference
 Sushil Kumar (2015)Indian Journal of Weed Science 47(3): 306–
320History, progress and prospects of classical biological control in
India .
 www.agritech.tnau.ac.in
 www.owalcation.com
 Mortenson, K. (1998). Biological control of weeds using
microorganisms. In: Boland, G. J., Kuykendal, L. D., eds. Plant-Microbe
Interaction and Biological Control. New York: Marcel Dekker, pp. 223–
248.
 Charudattan, R. (2001). Biological control of weeds by means of plant
pathogens: Significance for integrated weed management in modern
agroecology. BioControl 46:229–260.
 Published by the Biological Weed Control Committee of the Weed
Science Society of America Funding provided by the National
Biological Control Institute and the Weed Science Society of America.

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