MSc.

The study entitled “Bio- efficacy of post-emergence micro herbicides in transplanted rice (Oryza sativa L.)” was undertaken during the third crop/ summer season of 2011-‘12. The field experiment envisaged in the study was carried out in farmer’s field in Kanjirathady padasekharam, in Nemom Block of Thiruvananthapuram district. The objective of the study was to assess the bio-efficacy of two post-emergence micro herbicides, i.e., fenoxaprop-p-ethyl and cerfentrazone-ethyl in transplanted rice and to work out a suitable and economic weed management strategy.
The experiment was laid out in randomized block design with eight treatments and three replications. Two levels each of the new generation herbicides, fenoxaprop-p- ethyl (60 and 90 g ai ha-1) and carfentrazone-ethyl (20 and 25 g ai ha-1) and their combination (fenoxaprop-p-ethyl @ 60 g ai ha-1 + carfentrazone-ethyl @ 20 g ai ha-1), bispyribac sodium @ 30 g ai ha-1, hand weeding twice (HWT) at 20 and 40 days after transplanting and weedy check constituted the treatments.
A critical analysis of the data clearly pointed out that among the two new generation micro herbicides tested, carfentrazone-ethyl was a broad spectrum one comparable to or even better than the proven and popular new generation herbicide bispyribac sodium in many weed vegetation analysis parameters studied viz., absolute density, relative density, absolute frequency, relative frequency, weed dry weight, weed control efficiency etc. However, fenoxaprop-p-ethyl was observed to be an effective herbicide for grasses. The combination treatment ,i.e., fenoxaprop-p-ethyl @ 60 g ai ha-1 + carfentrazone-ethyl @ 20 g ai ha-1 also registered comparable values. The two doses of carfentrazone-ethyl tested, i.e., 20 and 25 g ai ha-1, were statistically on par with regard to their effect on the weed control parameters studied.
A perusal of the data on growth attributes of rice clearly indicated the favorable effect of weed management practices on plant height, number of tillers m-2 and dry matter production ha-1 especially with carfentrazone-ethyl @ 20 and 25 g ai ha-1, bispyribac sodium @ 30 g ai ha-1 and hand weeding twice treatments. All the weed management practices significantly improved the yield attributes of rice, viz., number of productive tillers m-2, grain weight panicle-1, number of spikelets panicle-1, number of filled grains panicle-1 and thousand grain weight compared to weedy check.
The different weed control treatments had significant impact on grain yield and economics also. The higher dose of carfentrazone-ethyl tested i.e., 25 g ai ha-1, recorded the highest grain yield, net income and B:C ratio (6790 kg ha-1, Rs. 67833 and 2.03 respectively) and it was statistically on par with its lower dose of 20 g ai ha-1 . However, bispyribac sodium @ 30 g ai ha-1 also registered higher grain yield (6401 kg ha-1) comparable to carfentrazone-ethyl @ 20 g ai ha-1; however, this positive effect was not manifested in net income and B: C ratio due to the high cost of this herbicide compared to carfentrazone-ethyl. The lowest yield was recorded by weedy check, which was significantly inferior to all other weed control treatments. Yield loss due to weeds was also maximum in weedy check (42.66 %). Net income and B:C ratio were comparatively low in HWT treatment eventhough yield obtained was substantially high (6111 kg ha-1), due to the high labour cost involved in the treatment.
Study of soil microbial population indicated that there was an initial reduction in the population of bacteria and fungi consequent to the application of the herbicides, compared to weedy check. However no significant change was noticed in actinomycetes population.
Conclusion
Considering the weed control efficiency, yield, economics and minimal application rate, the new generation herbicide carfentrazone-ethyl @ 20 g ai ha-1 at 20 DAT can be recommended for weed management in transplanted rice.