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- Biology and Control of Water Lettuce (Pistia stratiotes L.)
Biology and Control of Water Lettuce (Pistia stratiotes L.)
Dissertation Abstract:
Experiment were conducted to supply the life cycle of water lettuce (Pistia stratiotes L.) as affected by pH and nutrition, its competing ability with rice and other lowland weed species, its transpiration rate and growth stage sensitive to herbicide action.
Germination of Pistia after soaking for 20 days was found to be irregular; 25% germinated in 25 days, 50% in 28 days, and maximum germination was attained in 48 days. Pistia was also observed to germinate under water or anaerobically.
Offshoot production was very rapid; 130 offshoots developed within 2 months. Flowering started 2 months after planting. Flower initiation to seed maturity took 50-60 days. Life cycle of Pistia derived from sexual or asexual reproduction was completed in 5-6 months.
Growth and sexual reproduction of Pistia were found maximum at pH 7.
Rice in competition with Pistia significantly decreased in grain yield and dry weight, especially at lower levels of nitrogen application, indicating the weed’s strong competitiveness with rice for nitrogen.
Of the three weed species tested, Monocharia vaginalis (Burm.) Presl. Was the most competitive against Pistia, followed by Echinocloa crusgalli (L.) Beauv.Scirpus maritimus L. was the least competitive.
During summer months, daytime water loss by transpiration from the Pistia plant was 2.39 greater than that from free water, suggesting a need for more irrigation water in a rice field heavily infested with Pistia.
Pistia was more vulnerable to herbicides during the early development stage. Glyphosate (3.0 kg/ha), diquat (1.0 kg/ha) and C-288 (0.75 kg/ha) were effective killers of young Pistia, but a second application was needed to destroy the mature plants.
Pistia growing with rice could be effectively controlled by C-288 (0.75 kg/ha), but this herbicide was phytotoxic to rice. Benthiocarb (1.0 kg/ha) could fairly control Pistia without serious phytotoxicity to rice.