PhD

An investigation entitled "Integrated management of purple
nutsedge (Cyperus rotundus L.)" was conducted during 1999-2002 at
College of Agriculture, Vellayani, Thiruvananthapuram. It comprised of
one pot study, two field experiments and three laboratory experiments.
Pot experiment was conducted to study the biology of purple nutsedge
under various seasons and stage of tuberisation. Field experiments were
conducted to evolve an integrated management strategy for purple
nutsedge control in cropped area and a long-term control strategy in non-
cropped area. Laboratory experiments were conducted to assess the
allelopathic influence of purple nutsedge root exudates on early growth
of crop seeds and nutsedge extracts on weed seeds. An attempt has been
made to identify the allelochemicals present in tubers of nutsedge by
employing HPLC (High Performance Liquid Chromatography) technique.
In pot study, the growth and development of purple nutsedge was
observed for a period of one year. Results of the study indicated that
chain tuber took more time for sprouting compared to shoot tubers or
bulb. The time required to sprout varied with seasons in the case of
chain tuber and August and March planted tubers took lesser time for
sprouting. March and May planting tecorded more tuber production
compared to August and November planting. August planted tubers
recorded very early tuberisation and November and May planted tubers
took more or less double the time for tuberisation compared to August
planted tubers.
Field studies in cropped area indicated that the growth characters
of okra were significantly influenced by the weed management practices.
Flowering was early by about 7-10 days in mulched plots under both
stale seed bed and soil exposure treatments compared to weedy check
plots. Stale seed bed coupled with mulching registered maximum leaf
area index during both the years. All the weed control treatments except

where cowpea was raised as smother crop resulted in significantly more
fruits per plant and fruit yield per hectare. Maximum productivity of
5.24 t ha" was realised by stale seed bed with eucalyptus mulched plots
which was 171.5 and 11 per cent more than weedy check and weed free
plots respectively. The treatments had no significant influence on
quality attributes of okra like vitamin C, keeping 'quality, protein and
fibre content of fruits. Regarding soil fertility status, minimum
depletion of nutrients occurred in completely weed free and mulched
plots.
Stale seed bed with polythene mulching or pre and post emergent
glyphosate application were identified as the best nutsedge control
measure in cropped area. Post emergent glyphosate application after stale
seed bed has found to show spectacular inhibitory effect on nutsedge
multiplication and spread and this treatment recorded the highest
percentage reduction values for nutsedge control. Lowest rate of
regeneration was recorded by this treatment with lower viability of
tubers. The most economical treatment was stale seed bed with
glyphosate application integrated with eucalyptus mulching and it
recorded the highest net returns (Rs.18,2701-) and B:C ratio (2.01).
In non-cropped area. results of two seasons study indicated that
the effective stage for glyphosate spraying was identified as before tuber
initiation. The degree of inhibition exerted by glyphosate on regeneration
of nutsedge tubers was higher thanthat of 2.4-0. Among the summer
season treatments stale seed bed with irrigation followed by glyphosate
application was the best in achieving higher level of control.
In allelopathic studies. nutsedge root exudates collected at
sprouting stage inhibited the germination and growth of all the crop
seeds tested vi : .. rice. co wpea. sesamum. okra and brinjal. Also the
nutsedge extracts collected at different stages inhibited the growth and
development of Gomphrena de cumbe nse and Syne drell a nodij7ora.

The allelochemicals present in tubers of purple nutsedge was
identified by High Performance Liquid Chromatography (HPLC) and it
indicated the presence of p-hydroxy benzoic acid, p-coumaric acid, m-
coumaric acid, vanillic acid and gentisic acid.