Biological control of weeds

a green way to production...

1. Biological
control of weeds

2. What is biological
control?
Biological control covers two key concepts:
•the deliberate use of a weed's "natural enemies" to suppress its
population; and
•the use of these live organisms to maintain this lower population
density
The biological control approach makes use of the invasive naturally
occurring enemies.

3. Biological control of weeds
•It simply aims to reunite weeds with their natural enemies and achieve sustainable
weed control.
•A weed's natural enemies may be arthropods (insects, mites and their relatives),
bacteria or fungi
•These "control agents" feed upon or cause disease in the weed, thereby limiting its
growth, reproduction and spread
•The aim of biological control is to shift the balance of competition between the weed
and the crop in favour of the crop and against the weed.

5. Types of biological control:
Classical (inoculative) biocontrol:
•It involves the release of a relatively small number of control agents.
•These agents feed on the weed, reproduce and gradually suppress the weed as their
population grows.
•Generally arthropods are used as control agents.

6. Inundative biocontrol:
•In this type of biological control, large quantities of a control agent, generally a
pathogen are applied to weeds
•It uses large quantities of pathogens to create artificial disease epidemics
•It does not persist for long, requires to be reapplied

7. Conservation control:
•It is an indirect method, which manipulates the habitat around the weeds with the
aim of encourging those organisms that attack the weed.
•This is a long term strategy that requires a detailed knowledge of the ecology of the
crop weed habitat, the target weeds and the control agents.
•Livestock can also be considered as biological control agents which can give a broad
spectrum control of weeds in various situations.

8. How are biological
control agents
identified and
introduced?

9. Step 1: Identifying target weeds to be considered a good candidate for biological
control.
Step 2: Identifying control agents and assessing level of specialization
Step 3: Controlled release: All biological control agents must be approved under the
Plant Protection Act and are reviewed by an advisory panel of Agriculture
Step 4: Full release and identifying optimal release sites: If the agents survive the
harsh climate and damage or suppress the weeds in the controlled tests, they can be
released on other weed infestations

10. Step 5: Monitoring release sites: Release sites should be monitored periodically to
assess the size of the biological control agent population and the effect of the agent on
the weed.
Step 6: Redistribution (classical) If a biological control agent is released on a site with
favourable conditions, its population can grow quickly
Step 7: Maintaining control agent populations (classical)

11. Process of weed control
by biological agents.

12. •A weed becomes a problem as its population density is above a threshold at which it
affects the economic or ecological sustainability of the ecosystem
•Biological agents are released at this point
•Populations of biological control agents build up to very high levels due to the
abundance of host plant.
•Eventually their attack on the plant causes a decline in the weed population.
•It leads to a decline in the population of biological control agents until an
equilibrium is reached between the population of weeds & bio agents; such that this
new equilibrium is below the damage threshold that the ecosystem can tolerate

14. Some examples of
effective biological
control agents.

15. Bactra verutana has
been evaluated for
efficacy as a biological
control agent for C.
rotundus

16. The mycoherbicide
Dactylaria higginsii
is a biological control
fungus against
purple nutsedge
Bipolaris sp has
been effective
in control of
Johnson grass

17. Aceria malherbae used to control
field bindweed

18. Hyphena, Telionema &
Prospodium
tuberculatum- lantana
rust [clockwise from
left] has been effective
biocontrol agent for
Lantana sp.

19. •Some species of weeds do not have effective biological control agents.
•Some of them are
Cyanodon sp
Panicum sp
Argemone sp
•While species like Avena is being biologically controlled ants