Weeds represent a significant problem in Thailand’s sugarcane production. The various cycles of sugarcane cultivation result in degrees of weed severity in which each species requires a different weed control method, the most popular of which is the post-emergence herbicide method. However, sugarcane farmers often use incorrect rates, and operators’ safety is missing or applications are not selective, causing toxicity and interrupted growth of sugarcane. The effects of post-emergence herbicide types, time, and application rates are presented herein, through an experiment in Northeast Thailand, conducted in a randomized complete block design (RCBD) with four replications. The herbicides paraquat and ametryn were evaluated, with paraquat being more effective, yet resulting in higher toxicity and lower yield components. We may conclude through our experiments that ametryn and paraquat can be applied only once for sugarcane at the tillering stage and at rates of 540 and 2400 g ai ha⁻¹, respectively. These rates were lower than the recommended rates, which represented the minimum doses necessary to control Thailand’s dominant weed species like Brachiaria distachya (L.) Stapf., Dactyloctenium aegyptium (L.) P.B., Praxelis clematidea R.M King & H. Rob and Pennisetum polystachion (L.) Schult. Consequently, the adequate control of weeds is a rather case-specific situation and therefore each weed species should be taken into account.