Planting dates and rate of nitrogen fertilization influences whitefly population dynamics and incidence in cotton (Gossypium hirsutum L.)

A two-year study examined impact of planting date and nitrogen fertilizer on cotton yield and whitefly population dynamics and incidence. The study compared a local cotton variety and a hybrid variety planted at different sowing time and with varying nitrogen levels, under both protected and unprotected conditions. Very late planting of cotton led to 9.2–14% higher mean whitefly populations, especially during the whitefly’s peak activity period (15.82 and 21.67 whiteflies per three leaves during 2018-19 and 2019-20, respectively) at 38 Standard Meteorological Week (SMW). Observation recorded on nymphal counts revealed comparatively a smaller number of mean nymphs per three leaves (8.01 and 8.59 during 2018-19 and 2019-20, respectively) at early stages of crop growth (at 27 SMW) in very late sown crop having poor vegetative growth. As delayed sowing attained optimum growth it attracts comparatively higher nymphal population (13.36 and 10.96 during 2018-19 and 2019-20, respectively) at later stages of crop growth (at 33 SMW). Interestingly, there wasn’t much difference between protected and unprotected plots. Using more nitrogen fertilizer than recommended resulted in significantly higher whitefly numbers (14.21 and 15.60, during 2018-19 and 2019-20, respectively) throughout the season. Early (32.00 and 32.75 q/ha seed cotton yield, during 2018-19 and 2019-20, respectively) and timely planted cotton (30.94 and 32.50 q/ha seed cotton yield, during 2018-19 and 2019-20, respectively) produced significantly higher yields compared to very late planted cotton (19.66 and 21.63 q/ha seed cotton yield, during 2018-19 and 2019-20, respectively). Thus, timely sowing of cotton genotypes along with application of recommended doses of nitrogen is recommended for better cotton yields and to effectively manage whiteflies.