Allelochemicals Biologica... - Name

ALLELOPATHY FOR WEED CONTROL 117
6. ALLELOPATHY AND INTEGRATED WEED MANAGEMENT
Because of limited resources, an average farmer in a developing country can neither
afford to take big economic risks nor opt for technologies associated with a lot of
external inputs. As a result, research on vegetation management strategies capable of
minimizing weed infestation and simultaneously favoring sustainable crop production
that are economical and eco-friendly needs attention (Akobundu, 2000). Allelopathy
fits in to this approach as one of the integral principles in any such cropping systems
involving crop rotation, inter-cropping, cover crop, and off-season land management
(such as raising green manures and ploughing in situ). Linking similar integrated
farming approaches to integrated weed management and integrated pest management
helps to address bio-diversity concerns with a simultaneous reduction in agrochemical
use especially in low input agriculture and small hold farms. A 3-yr study of weed
management in wetland transplanted rice, rice - mung bean cropping sequence with
treatments assigned to the same plots every season at Annamalai University revealed
that lowland weeds like C. difformis was drastically reduced by the introduction of a
relay crop of mung bean in the sequence (Kathiresan, 2002). Raising a green manure
crop of Sesbania aculeata Poir in the off-season (May - July) and ploughing it in situ
at the age of 45 days, before the cultivation of rice in the first (August - January) as
well as second (January - April) season, helped in reducing weed competition in both
the rice crops (Gnanavel and Kathiresan, 2002). Off-season land management such
as raising green manure crop significantly reduced the weed seed reserves in the soil
through allelopathic interference, whereas rotation of an upland crop like mung bean
with rice interrupted the weed flora in lowland through mung bean residues.
Integrated weed management assumes significance in managing aquatic systems.
Use of herbicides are constrained with drastic reduction in water quality and ultimate
ill effect on associated non-target organisms. In countries like India, herbicides are
yet to get registered for use in aquatic systems. Under these conditions managing
infestations of water hyacinth, water fern, and water lettuce is challenging. In one of
the recreational lakes with tourist attraction in a hill resort in Ooty, in the state of
Tamilnadu, India, the public authority has spent heavily (Indian Rupees 1.25 crores,
about US $200,000) for manual clearing of water hyacinth for one time. Similarly,
thousands of army personnel were used for clearing water hyacinth in a lake in
Bangalore, the capital city of Karnataka State, India. Classical biological control is
the only option available and that too is difficult in situations where the water body
dries off in the peak summer, leaving the released insects to starve and die due to
interrupted host range. Accordingly, integration of short term control measures with
classical biocontrol might offer excellent results. Allelopathy reinforced classical biocontrol
research has been targeted and taken up at Department of Agronomy,
Annamalai University through National Agricultural Technology Project funded by
Indian Council of Agricultural Research. This project originated from the basic concept
of allelopathic inhibition of water hyacinth by C.amboinicus as mentioned earlier.
However, the requirement of plant product for treating larger watersheds might pose
practical difficulties. Previous results also indicated that if absorbed in to plant through