Field Efficacy of few Insecticides as Soil Application against Potato White Grubs in Assam

Abstract

A field experiment was conducted during winter (rabi) seasons of 2006-09 to find out the effectiveness of six insecticides as soil application against Lepidiota mansueta, a severe key pest of potato at Majuli river island of Jorhat, Assam. Experimental results indicated all the insecticides were found to be significantly superior in respect of per cent reduction of damage based on both weight and number basis over the untreated control. However, quinalphos 25EC @ 400 gm a.i. /ha recorded lowest tuber damage (10.22 %) and highest tuber yield (86.72 ql/ha) with B:C ratio of 10.11:1. The pesticide residue analysis did not showed any detectable amount of quinalphos in potato samples collected at harvest.  Based on the superiority of quinqlphos 25EC @ 400 gm a.i. /ha over other insecticides tested against L. mansueta grubs in potato, an on farm trial (OFT) was conducted at Dhubri in 2009-10 in collaboration with KVK, Dhubri, Assam. The OFT results indicated that the quinalphos 25 EC @ 400 gm a.i /ha treated plots recorded 3.91 and 2.26 per cent tuber damage (based on weight basis) as against 16.04 and 15.00 in untreated control plots respectively in Kufri Megha and Kufri Giridhari varieties. The tuber yield was found to be 225.67   q/ha & 233.33 q /ha (quinalphos treated plots) and 196.44 and 209.70 q /ha (in control plots) respectively in Kufri Megha and Kufri Giridhari varieties.