MSc

Knowledge on biology and ecology of weeds and its interaction with rice plays a key role in weed management. In the research programme entitled ‘Morphology, ecology and management of Monochoria vaginalis (Burm. f.) Kunth’, Monochoria vaginalis, a broad-leaved monocot weed of wet land paddy was seen to occur in all the major rice ecosystems of Kerala viz., Kole, Palakkad, Pokkali, and Kuttanad, but was not seen in drier parts. It is an emergent annual hydrophyte herb, and has the potential to grow perennially through rhizomes. The plant showed great morphological variation with location, due to the prevailing ecological situation including soil factors. Monochoria grew vigorously with increased soil fertility and favoured slightly acidic condition, but could not tolerate high salinity.

Monochoria vaginalis was observed to have fibrous root system, with the stem modified into a short rhizome from which soft hollow leaf petioles arose. The plant height varied from 10 to 60 cm, number of leaves from 5 to 16, leaf area from 10 to 70 cm2, and the dry weight ranged from 1.92 g to 5.70 g per plant. The leaf shape changed from narrow in the juvenile stage to cordate in the mature stage and the major portion of leaf lamina was occupied by air chambers.

About 4 to 9 bluish purple coloured flowers were borne on spicate inflorescences and the total number of flowers per plant ranged from 6 to 48. The flowers opened in the morning and were spirally contorted later. Inflorescence bent to form capsules, which split into three valves at maturity and released numerous longitudinally ribbed seeds. Monochoria is propagated mainly through seeds, and showed dormancy immediately after shedding, which may be influenced by the season. The mean number of seeds per capsule ranged from 116 to 277, total number of seeds per plant from 3400 to 11,300 and 1000 seed weight from 0.27 g to 0.82 g.

The effect of depth of burial and flooding depth and duration on germination of Monochoria vaginalis was studied by two separate pot culture


experiments. Monochoria seeds germinated on soil surface, but when placed below 2 cm depth, germination was inhibited due to lack of light. The seed germination in Monochoria was significantly influenced by flooding depth and duration. Greater germination was obtained when seeds were kept at saturated and low flooded depth of less than 5 cm for more than 4 days. Increased flooding depth decreased the germination percentage.

Influence of environmental factors like light and temperature, pH, and salinity on germination of Monochoria vaginalis was investigated separately in lab conditions. The seeds kept in solutions of pH 6 and 7, germinated while no germination took place in solutions of pH 4, 5, 8 and 9. Saline solutions with concentrations ranging from 25 to 250 mM NaCl inhibited the germination, and the seeds germinated only in 0 mM NaCl concentration, or non-saline solutions.

Influence of light and temperature was studied in a seed germinator, in which light, temperature, and humidity conditions could be regulated. Seeds kept in continuous dark condition failed to germinate, irrespective of the temperature provided. Germination was observed at a temperature of 38oC in continuous light, and alternate light and dark condition, but did not germinate at 28oC and 33oC in any of the light conditions provided. From the current investigation, it was clear that Monochoria vaginalis germinated only in light condition under anaerobic, saturated or submerged situation.

All the tested herbicides namely, 2,4-D, Almix®, ethoxysulfuron, bispyribac sodium, penoxsulam and cyhalofop butyl + penoxsulam, were found to be very effective in controlling Monochoria by two weeks after application. However, 2,4-D caused severe injury on the weed immediately after application and brought about complete kill within one week of application. The premix herbicide, cyhalofop butyl 5.1 % + penoxsulam 1.02 %, was also good at killing Monochoria within a short period. From this study it is concluded that all the six post-emergence herbicides tested can be recommended to control Monochoria vaginalis in rice at 20 DAS.