Field efficacy of six different insecticides were evaluated against the grubs of L. mansueta in potato at the farmer’s field of Pohadiya village, Majuli, Assam during 2013-15. The required amount of insecticides was applied in seed furrows by incorporating with pulverized soil before sowing of the potato tubers. Experimental results indicated that all the insecticidal treatments were significantly superior in respect of per cent reduction of tuber damage as well as reducing the number of grubs per square meter over the untreated control. However, the plots treated with chlorpyriphos 10 G @ 2 kg a.i./ ha recorded lowest per cent of tuber damage (3.11 and 2.74 % both in weight and number basis) as well as least number of grubs (3.50) resulting in a marked increase in tuber yield of 119.91 q/ ha. On the other hand, untreated control recorded lowest yield (91.80 q/ ha) with a very high levels of infestation (28.79 and 28.94 based on weight and number, respectively) of tubers caused by the grubs of L. mansueta. Highest B: C ratio was registered in chlorpyriphos 10 G @ 2.0 kg a.i./ha (2.69:1) treated plots followed by clothianidine 50 WDG @ 120 g a.i./ ha (1.50:1) and imidacloprid 70 WG @ 300 g a.i./ ha (1.44:1).