Effect of glyphosate on weed control and growth of oil palm at immature stage in Ghana

Abstract Chemical weed control is recognized to be an economical practice in oil palm plantations as it can reduce reliance on manpower for hand weeding. A study was conducted at the Benso Oil Palm Plantation to evaluate the efficacy of “Glisat” a glyphosate with trade name “GLISAT 480SL” with that of “Ceresate” an approved glyphosate on the market on a plot planted to two year old oil palm trees. Treatments consisted of untreated plot, different doses of Glisat at 0.8 L/ha, 1.4 L/ha, 2.8 L/ha, 4.3 L/ha and Ceresate 1.5 L/ha. Result showed that Glisat dose at 1.4 - 2.8 L/ha is as effective as Ceresate 1.5 L/ha in controlling weeds, however, the efficacy differs slightly in the first two weeks after treatment. No significant differences was observed between Ceresate 1.5 L/ha and Glisat at 1.4 L at 8 weeks after treatment (WAT). Herbicide efficacy of Glisat 1.4 L/ha was higher than Ceresate 1.5 L/ha for grasses, but no difference was observed for the broadleaves. Both Glisat and Ceresate reduced dry weights of weeds significantly, and 4 WAT was the optimum period to observe high weed mortality. Glisat was effective in controlling both broadleaves and grasses even though the effect on grasses was higher. Glisat and Ceresate had no adverse effect on the oil palm and significantly improved vegetative parameters by reducing competition with weeds for nutrients and other growth resources. Glisat could be applied at 2.8 L/ha as its effects was comparable to Ceresate 1.5 L/ha at 4 WAT.