INFLUENCE OF SELECTED ENVIRONMENTAL-FACTORS ON GLYPHOSATE EFFICACY WHEN APPLIED TO AWNLESS BARNYARD GRASS (ECHINOCHLOA-COLONA (L) LINK)

Glasshouse experiments were conducted to determine the effects of vari ous environmental factors on glyphosate efficacy when applied to Echin ochloa colona (L.) Link (awnless barnyard grass) plants. The variables examined were 4 soil moisture conditions (29, 42, 55, and 100% of fie ld capacity), 2 levels of irradiance (400 and 800 mu mol/m(2).s), 3 te mperature regimes (20/15, 30/25, and 35/30 degrees C; day/night), and 2 levels of relative humidity (92 and 65%). The efficacy of 360 g acid equivalent glyphosate/ha was greatest when applied to well-watered (f ield capacity) plants that were placed under cool (20/25 degrees C) an d humid (92% relative humidity) conditions. The efficacy was least whe n applied to plants under severe water stress (29% of field capacity) that were placed under hot (35/30 degrees C) and less humid (65% relat ive humidity) conditions. In all experiments, efficacy was not altered by the level of irradiance.