The effectiveness of three herbicides mixed with metsulfuron methyl in controlling weeds on two types of soil in smallholders oil palm plantation

Field experiment was conducted on six-year oil palm plantation in Central Bengkulu Regency in 2012 to evaluate the efficacy and cost effectiveness of three herbicides mixed with metsulfuron-methyl in controlling weeds on mineral and peat soil. The experiment was laid out in Randomized Complete Blocks Design (RCBD) with three replications. Seven herbicide treatments consisted of control (check), paraquat at 600 g active ingredient (a.i) ha-1, glyphosate at 600 a.i. ha-1, oxyfluorfen at 600 g a.i. ha-1, paraquat at 600 g a.i. + metsulfuron-methyl at 75 g a.i. ha-1, glyphosate at 600 g a.i + metsulfuron-methyl at 75 g a.i. ha-1, and oxyfluorfen at 600 g a.i. + metsulfuron-methyl at 75 g a.i ha-1. The results showed that: (1). Composition and weed species on peat soil were more complex and various than on mineral soil. (2). Paraquat and oxyfluorfen on single application were not effective to control weed on peat soil, meanwhile glyphosate was effective to control weeds on both mineral and peat soil. (3). The duration of effective weed control on mineral soil (9 -12 weeks) was longer than on peat soil (6-8 weeks) on various herbicide treatments. (4). Glyphosate on single application had the most cost effectiveness in controling weeds on both mineral and peat soil. (5). Glyphosate is sugested to be used in mature oil palm provided by its efficacy, cost effectiveness and safety for human and environment. Proper choice and use of herbicide has broad impact not only on the growers but also on human health and environmental safety.