1. BIOLOGICAL
CONTROL
Agents
By Allah Dad
Khan

2. Biological control work in progress
Agents currently being tested:
1. scentless chamomile (Matricaria perforata) with the Austrian stem-
mining weevil Microplontus edentulus and the gall midge
Rhopalomyia sp.
2. yellow toadflax (Linaria vulgaris) and Dalmatian toadflax (L.
dalmatica) with the stem-mining weevil Mecinus janthinus and
yellow toadflax with the root- mining moth Eteobalea serratella
(Figure 10)
3. field bindweed (Convolvulus arvensis) with the gall- forming mite
Aceria malherbae
4. cleavers (Galium spurium) with the gall mite Cecidophyes
rouhollahi
5. hound's-tongue (Cynoglossum officinale) with the root weevil
Mogulones cruciger
6. purple loosestrife (Lythrum salicaria) with foliage feeding beetles of
the genus Galerucella

3. Criteria for Selection of Bio-agent or Qualities of
Good Bio-agent for Weed Control
1) Host Specificity:
a) The bio-agent recommended for weed control should
be host specific i.e. the bio-agent must feed or kill only
the host plant (Weed).
b) It should not harm or feed the crops and other useful
(economical) plants. Starvation test is conducted for
this purpose before using the bio-agent for weed
control.
2) Bio-agent Hardiness:
a) The bio-agent should be hardy and must adopt or
withstand the new environment in which it is to be
used.
b) It should be free from its natural enemies like
predators and parasites.
c) It should be capable of surviving in a situation of
food shortage for longer period.

4. Criteria for Selection of Bio-agent or
Qualities of Good Bio-agent for Weed
Control contd
3) Feeding Habit:
a) It must be able to kill the host or at least prevent
seed production or reproduction of host plant.
b) The bio-agent should be capable of seeking the
host.
c) It should be a heavy feeder and consume or
cause the death of large population of host
rapidly.
4) Base of Multiplication:
The bio-agent should have high rate and ease of
natural
reproduction to control the host plant in short time.
If the
natural rate of reproduction is less than more
times

5. Different Bio –agent Used for
Controlling Weeds
Below are the different bios –agent used for
controlling weeds
1) Insects
2) Carp fish
3) Snails
4) Mites
5) Fungi and
6) Competitive plants.
The long term experiments with great care are
conducted for searching a host specific bio
agent. The outstanding and feasible
examples of biological control of weeds are
given below:

6. Different Bio –agent Used for
Controlling Weeds
1) Use of Insects:
a) Lantana camara ( Ghaneri) – was controlled by
using Crocidosema lantana Busck, a moth as
most promising bio-agent in Haweli- This bio-
agent feeds on flowers and seeds.
Lantana bug ( Teleonemia scruplosa stall) was
used in Australia for controlling Ghaneri.
Hispine beetles ( Octotoma scabripennis and
Uroplate girandi were also used in Australia for
control of Ghaneri.
b) Prickly pear/cactus (Opuntia spp) by using
cochineal scale insects. ( Dactylopis indicus and
Dactylopius tomentosus in south India and in
Australia by using Cactoblastis cactorum.

7. Different Bio –agent Used for Controlling
Weeds
c) Alligator weed ( Altermathere
philoxoroides ) in U.S.A has been
effectively controlled with flea beetle
(Agasicles hygrophyla)
d) Fern (Salvinia molesta) in kerela
(India) by using a beetle called
Cytrobagous saviniae.
e) Cypenis rotundus (nustsedge ) in
India U.S.A and Pakistan by Bacteria
spp a shoot borer moth.

8. Different Bio –agent Used for
Controlling Weeds
2) Use of Carp Fish:
Common carp ( Cyperus carpio) and
Chinese carp ( White amur or grass
carp) called Clenopharyngodon idella for
control of aquatic weeds.
3) Snails:
(Marisa cornuarietis ) and certain fresh
water snails are useful to control aqutic
weeds like water hyacinth, salvinia spp.
and water lettuce.

9. Different Bio –agent Used for
Controlling Weeds
4) Use of Mites:
A spider mite (Tetranychus desertorum ) was used in
Australia foe control of prickly pear ( cactus).
5) Use of Fungi:
a) Acacia glauca was controlled in Hawali by injecting
suspension of spare of cephalosporium spp.
b) Rhizoctonia blight for control of water hyacinth.
c) Use of Mycoherbicides / Bioherbicides.
Bioherbicides approach involves spray of specific fungal
spores or its fermentation products , against the target
weed. These preparations are called mycoherbicides (
Bioherbicides). Mycoherbicides can be specific
(Selective) or non-specific (Non selective) and are used
just like chemical herbicides in developed countries.
Control of weeds by using the mycoherbicides is called
bio-herbicidal control of weeds.

10. Different Bio –agent Used for Controlling
Weeds
6) Use of Competitive Plants:
a) Use of Rajagira (Amaranthus
panjculatus ) for control of nutsedge (
nutgrass) and other weeds as it is the
best smother crop and also produces
allelopathic effect.
b) Use of smother crop like soybean,
cowpea, greengram, Sanhemp, Sweet
potato, etc. in crop rotation for control of
weeds.
c) Proper crop rotation is helpful for
management of crop associated and
parasitic weeds.

11. Biological Weed Control V/s other Methods
of Weed Control
1) The initial cost of biological weed control
appears to be high, but when compared to the
cost of developing new herbicides, it is quite
reasonable.
2) This method is so far adopted for control of
weeds in non cropped areas and not useful for
controlling different weed species in cropped
lands.
3) Minimum damage to the environment by
biological method of weed control as compared
to other methods of weed control.
4) This method is not solution for all weeds but
used for larger weeds or particular weed species.
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