MSc

Lab and field experiments were conducted at the Instructional
farm, College of Agriculture, Vellayani to study the allelopathic influence of
Purple nutsedge (Cyperus rotund us L) on important field crops; to investigate
the effectiveness of systemic herbicides for control of nutsedge and also to assess
the effect of chemical weed control on growth and yield of subsequent field
crops.
In Ex. no. I, allelopathic influence of purple nutsedge on
important field crops like rice, ragi, cowpea, green gram, bitter gourd and bhindi
were studied. The treatments comprised of aqueous extracts and blended
extracts of fresh and dry plant parts of nutsedge. The results revealed that
aqueous extracts of nutsedge inhibited germination of rice, ragi, bitter gourd and
bhindi while it had some stimulatory effect on germination of cowpea and green
gram. The early growth characters of the field crops were found suppressed by
the aqueous extract treatment while the blended extract showed no effect. In
general, the dry plant parts showed greater effect than the fresh material.
Under Ex.no.Il, field studies were made to investigate the
effectiveness of systemic herbicides viz. Glyphosate and 2,4-D for control of
nutsedge. The treatments included different doses of the herbicides with and

without adjuvants and Glyphosate combined with sublethal dose of 2,4-D. The
results revealed that lowest dose of the herbicides were sufficient for complete
kill of the purple nutsedge plants in the experimental area and there was no
regrowth upto 6 weeks. There was significant reduction in viability of tubers
collected one month after herbicide application, but the tubers tested 45 days
after spraying showed an increase in germinability over the record on 30th day.
Tubers from treatments involving Glyphosate with sublethal dose of 2,4-D
recorded the lowest sprouting percentage indicating the possibility for weed
control for a longer period.
In Ex. no. In, the persistence of the herbicides in soil were
monitored and it was observed that early growth of cucumber sown on the same
day of herbicide application was affected while that sown on soils collected 10
days after spraying recorded growth characters comparable to that of control.
From Ex.no.IV, it could be inferred that chemical weed control
did not show any deleterious effect on growth and yield characteristics of ragi
and cucumber sown 15 days after the treatments. Application of 2,4-D for
nutsedge control was found superior to other treatments in terms of net income
and B:C ratio and the lower unit cost of the chemical was precisely the reason
for its superiority.