POPULATION DYNAMICS AND GROWTH OF WEEDS IN RAINFED RICE-ONION SYSTEMS IN RESPONSE TO CHEMICAL AND CULTURAL CONTROL METHODS

摘要

A field study was conducted to determine the effects of tillage in combination with chemical control and handweeding on the population dynamics, growth and control of weeds in rainfed rice-onion systems. Twelve weed species were associated with onion but only Cyperus rotundus L, Echinochloa colona (L.) Link and Trianthema portulacastrum L. were dominant in terms of density and fresh weight. Tillage alone did not affect the growth of the three most dominant weeds. However, a shift in weed dominance was observed in response to weed control methods. Pre-plant application of glyphosate (1.1 kg ai/ha) at 14 days before transplanting (DBT) followed by one handweeding (HW) was as effective as the application of oxyfluorfen (0.06 kg ai/ha) followed by three HW (farmer's practice) in controlling weeds. In conventional tillage, comparable bulb yield was obtained in plots applied with pre-plant glyphosate at 14 DBT followed by one or two HW and the farmer's practice. In deep and shallow tillage, bulb yield in plots treated with glyphosate followed by one HW was lower than the farmer's practice but was comparable with the weedfree check and those applied with glyphosate followed by two HW. Percentage yield loss was comparable between the application of glyphosate at 14 DBT followed by one HW and the farmer's practice. As weed density in the field was high, 60 mandays were needed to handweed a hectare of onion. Farmers can save 60% in weed control costs when glyphosate was applied at 14 DBT followed by one HW compared with the farmer's practice.