Effect of mineral oil and its combinations against leafhopper, Amrasca biguttula biguttula in okra
Laboratory and field studies were conducted on the bioefficacy of mineral oil and its combinations against leafhopper, Amrasca biguttula biguttula (Ishida) in okra. In addition, their safety to natural enemies, pollinators and their phytotoxic effects on okra were also studied under green house and laboratory conditions on okra revealed that 2 per cent concentration of mineral oil + neem oil and mineral oil + karanj oil were superior and effective over other treatments both with 93.3 per cent mortality of hoppers at 48 HAT. In pot culture experiments, the efficacy of mineral oil + neem oil and mineral oil + Karanj oil, at 2 per cent concentration were superior and effective against leaf hopper, with a mean population reduction of 79.9 and 79.3 per cent. In field experiments, mineral oil + neem oil, mineral oil+ Karanj oil and mineral oil at 2 per cent concentration significantly checked the leaf hopper population with a mean population reduction of 84.1, 80.6, and 78.3 per cent leaf hoppers, respectively. The foliar application of mineral oil on okra revealed that upto 5 per cent concentration showed no phytotoxic effects like wilting, vein clearing, necrosis, epinasty and hyponasty on both 30 and 45 days old plants. However, mineral oil treatments of 7, 10, 15 and 20 per cent concentration showed leaf injury to tip and leaf surface with a rating of 2.0, 2.0, 3.3 and 6.3 on 30 days old plants and 2.0, 2.0, 3.0, 5.0 on 45 days old plants, respectively. All the mineral oil based treatments were found safer to egg parasitioid Trichogramma chilonis (Ishii) with the adult emergence and egg parasitization of 92.4-93.8 and 92.4-96.0 per cent, respectively. The laboratory experiments conducted on the safety of mineral oil and its combinations to Chrysoperla carnea (Stephens) eggs and grubs, revealed that all the mineral oil based treatments were safe with negligible negative effect on the hatching of eggs showing 89-93.5 per cent hatching and minimum grub mortality of 3.3-16.6 per cent. The mineral oil based treatments at 2 per cent concentration were found safe to Apis cerana indica with minimum mortality of 3.3-10 per cent of worker honey bees.