Influence of sowing date and weather parameters on the relative abundance and damage of major insect-pests of wheat in North-Western plains of India

Field studies were conducted during 2017–18 and 2018–19 to investigate the relative abundance and damage of major insect pests of wheat sown under four different sowing times (early, timely, late and very late). Rhopalosiphum maidis and R. padi species of aphids were more abundant during vegetative stages while Sitobion miscanthi, S. avenae and Schizaphis graminum species were recorded at earhead stage. The peak populations of 21.4, 22.8, 20.2 and 19.2 aphids per tiller were recorded in 8^th, 9^th, 10^th and 11^th in early, timely, late and very late sown crop, respectively during 2017–18. However, the peak of aphid population was recorded in 10^th & 11 SMW in early and timely/late/very late sown crop, respectively during 2018–19. The aphid incidence got delayed with the delay in sowing time. The most vulnerable milky grain stage in the early sown crop (7–8 SMW) escaped the peak of aphid population while this stage coincided with peak of aphid attack in timely (9- 10 SMW) and late sown (9- 10 SMW) crop. The regression analysis of weather parameters showed that aphid incidence was not affected by any weather parameter in early sown while maximum and minimum temperature had significant positive effect on population build-up of aphids in timely sown wheat crop. With every one degree rise in maximum and minimum temperature, 2.05 and 3.88 fold increases in aphid incidence was observed in timely sown crop. Minimum temperature and morning relative humidity exerted their effects onlate and very late sown wheat crop. With every one degree rise in minimum temperature, 3.51–3.85 fold increase in aphid incidence was recorded in late and very late sown crop. At the same time, withevery one per cent rise in morning relative humidity, 1.97–1.98 fold increase in aphid population was recorded. The termite and pink stem borer damage was significantly higher in early sown crop as compared to timely and late sown crop during 2017–18. Relatively lower damage of termites and PSB was recorded in 2018–19 which could be attributed to lower minimum temperature (>2°C) in December in 2018–19.