Allelochemicals Biologica... - Name

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RAMANATHAN KATHIRESAN, CLIFFORD H. KOGER , KRISHNA N. REDDY
foliage, the plant product could be very effective even under very low doses (0.1 g
L -1 ). The only hurdle faced for application of the plant product on the foliage is retention
of plant product due to the repulsion by leaf cuticle. Any rupture and/or damage to
leaf cuticle could potentially enhance absorption of plant product. To this end, the
well established insect bio-control agents in India, Neochetina bruchii Hustache /
eichhorniae Warner were chosen for the study to serve as a component of integrated
weed management. These weevils normally scrape on the leaves of water hyacinth.
An attempt was made to integrate both these bio-control tools viz. classical biocontrol
using N. bruchii / eichhorniae and application of the plant product C.
amboinicus. Integrating both the tools are possible with two different sequences.
Treating the water body first with plant product at a lesser dose with the expectation
that it will reduce the vigor of the weed, predisposing it for faster and rapid destruction
by the insect agents that are to be released later is one possibility. Whereas releasing
the insect agents first on the weed host, allowing them to make leaf scrapings that
might help foliar uptake of plant product that could be sprayed later is another. Both
these sequences were compared in the study. It was observed that treating the water
body first with plant product followed by the release of insect agents on the weed
showed an antagonistic interaction, as the insects migrated from treated, partially
killed plants to healthy plants. The second sequence of releasing the insect agents
first followed by spraying of the plant product on the weed foliage produced an additive
or synergistic response with rapid and complete weed control with in a single season.
The optimum inoculation loads of insect agents, concentration of the spray fluid of
plant product required, length of interlude between the release of insect agents and
spraying of plant product were standardized for all three different growth stages of
the weed, and the success of this integrated approach was demonstrated at three different
watershed environments in the state of Tamilnadu, India. The plant product was also
shown to be safe for the insect agents with out inducing migratory behavior and
without causing any histo-pathological injury on different tissues of the insects like
salivary gland, gut, cutin, testis, and brain. Further, the integrated approach also
proved safe for non-target organisms and water quality (Kathiresan, 2004b).
7. CONCLUSIONS
Plants can interfere with each other through allelopathy or competition for resources.
Allelopathy can be used in weed management in several ways including cover crops,
smother crops, green manure crops, breeding for allelopathic crop cultivars, mulching
and crop residue management. Allelopathic suppression of weeds will not replace
synthetic herbicides which are the dominant method of weed control in many countries
nor will it be economically competitive with herbicides. However, allelopathy can fit
in an integrated weed management strategy very well as a vital component. This
approach could reduce the sole dependence on synthetic herbicides for solving many
complex weed problems. The examples discussed herein include an aggressive rice
cultivar for complimenting weed control in direct seeded rice and plant productreinforced
classical bio-control (through weevils) of water hyacinth.